2.1.1 Bacterial polysaccharides
2.1.1 細菌多糖

The most prevalent bacterial polysaccharides are extracellular, exo-polysaccharides (EPS), and capsular polysaccharides (CPS). Interestingly, some bacterial strains also synthesize unexpected polysaccharides for prokaryotes such as cellulose, alginate, and fructans like inulin and levan (Coté et al., 2008; Robyt, 1998). EPS consists of carbohydrates, mainly in the α-pyranoside form, and are organized in an amorphous layer surrounding the bacterial cell or are secreted outside into biofilms. They may be further organized into another structure, the CPS (Yates et al., 2021). EPS are composed of homopolysaccharides like α-D-glucans, β-D-glucans polysialic acid, etc. (Figure 1) and heteropolysaccharides like xanthan, gellan, fructans, wellan, rhamsan, etc. (Figures 2 and 8; Nwodo et al., 2012). CPS are diverse classes of high-molecular-weight polysaccharides produced by both gram-negative and gram-positive bacteria, which have similar structures and properties as EPS (Ovodov, 2006).
最普遍的細菌多糖是細胞外多糖、胞外多糖 （EPS） 和莢膜多糖 （CPS）。有趣的是，一些細菌菌株還合成了原核生物的意想不到的多糖，如纖維素、藻酸鹽和果聚糖，如菊粉和萊萬（Coté等人，2008 年;Robyt，1998 年）。EPS 由碳水化合物組成，主要以 α-吡喃糖苷形式存在，組織在細菌細胞周圍的無定形層中，或分泌到外部的生物膜中。它們可以進一步組織成另一個結構，即 CPS（Yates et al.， 2021）。EPS 由 α-D-葡聚糖、β-D-葡聚糖、多唾液酸等同多糖組成（圖 1）和黃原膠、結冷糖、果聚糖、Wellan、鼠李糖等雜多糖（圖 2 和 8;Nwodo et al.， 2012）。CPS 是由革蘭氏陰性菌和革蘭氏陽性菌產生的不同類別的高分子量多糖，它們具有與 EPS 相似的結構和特性（Ovodov，2006 ）。

EPS isolated from Pseudomonas entomophila PE3 applied on sunflower seeds (Helianthus annuus L.) stimulated growth and stress resilience under saline-field conditions (Fatima and Arora, 2021). Another study showed that EPS from Bradyrhizobium sp. IC-4059 coated on seeds of pigeon peas (Cajanus cajan (L.) Millsp.) enhanced plant volume, nodulation, seed yield, and protein content and stimulated the growth of indigenous soil rhizobia (Tewari et al., 2020). Nonetheless, very few studies are available on bacterial EPS as biostimulants. However, several studies on EPS-producing bacteria, species like Pseudomonas aeruginosa, Azotobacter vinelandii, Sphingomonas paucimobilis, Azotobacter sp., Paenibacillus sp., Klebsiella sp., Bacillus sp., and Pseudomonas spp., have shown that they help to increase water permeability, nutrient uptake through roots, soil stability, soil fertility, plant biomass, chlorophyll content, root and shoot length, and surface area of leaves, while also helping to maintain metabolic and physiological activities during drought stress (Bhagat et al., 2021).
從嗜昆蟲假單胞菌 PE3 中分離的 EPS 應用於葵花籽 （Helianthus annuus L.） 在鹽田條件下刺激生長和抗逆性（Fatima 和 Arora，2021 年）。 另一項研究表明，塗覆在木豆 （Cajanus cajan （L.） Millsp.） 種子上的 Bradyrhizobium sp. IC-4059 的 EPS 提高了植物體積、結瘤、種子產量和蛋白質含量，並刺激了本地土壤根瘤菌的生長（Tewari 等人， 2020 年）。儘管如此，關於細菌 EPS 作為生物刺激劑的研究很少。然而，對產生 EPS 的細菌的幾項研究表明，如銅綠假單胞菌 、醋固氮桿菌 、 鞘氨醇單胞菌、固氮桿菌屬、 泛芽孢桿菌屬、 克雷伯氏菌屬、 芽孢桿菌屬和假單胞菌屬，它們有助於提高透水性、根系吸收養分、土壤穩定性、土壤肥力、植物生物量、葉綠素含量、根和芽長，以及葉子的表面積，同時還有助於在乾旱脅迫期間維持代謝和生理活動（Bhagat 等人， 2021 年）。

Gellan gum (Figure 2) and oligo-gellan coated on bulbs of Eucomis bicolor and E. comosa enhanced fresh weight of leaves and bulbs, chlorophyll content, net intensity photosynthesis, and macronutrient content in leaves (Salachna et al., 2018b). Drenching treatments with oligo-gellan on Perilla frutescens (L.) Britt. promoted plant growth, fresh weight of the aerial parts, antioxidant activity, and accumulation of nitrogen, potassium, magnesium, and phenolics. Such treatments also alleviated the negative effects of salt stress by limiting the loss of biomass, macronutrients, and phenolics by accumulating less sodium and having more photosynthetic pigments and antioxidant activity (Salachna, Grzeszczuk & Mizielińska, 2019). EPS are also known to be virulence factors for many plant pathogenic bacteria. Moreover, some plants can recognize EPS from specific bacteria, which can trigger the salicylic acid (SA) pathway and promote defense-gene expression and production of ROS (Milling et al., 2011). In addition, several purified components of EPS and CPS have a well-known elicitor activity. Indeed, β-D-glucans from bacterial cell walls elicited plant defense responses such as the induction of chitinase and phenylalanine ammonia-lyase (PAL) activities and the synthesis of isoflavanoids and phytoalexins (Chaliha et al., 2018). Bacterial fructans can be considered as microbe-associated molecular patterns (MAMPs) in plants due to their hydrolysis by fructan exohydrolases generating fructooligosaccharides (FOS), which can prime plant defenses (Versluys et al., 2017). Xanthan (Figure 2) is an important factor in bacterial pathogenicity and can elicit defense mechanisms in certain plant species by altering peroxidase activity (Luiz et al., 2016). Rhamsan has also been shown to induce the production of phytoalexins, including anthraquinones in Morinda citrifolia (Doernenburg and Knorr, 1994).
Eucomis bicolor 和 E. comosa 鱗莖上塗覆的結冷膠（圖 2）和低聚結冷膠提高了葉片和鱗莖的鮮重、葉綠素含量、凈強度光合作用和葉片中的常量營養素含量（Salachna 等人， 2018b）。用寡聚糖對紫蘇 （L.） Britt 進行淋濕處理。促進植物生長、地上部分的鮮重、抗氧化活性以及氮、鉀、鎂和酚類物質的積累。這種處理還通過限制生物質、大量營養素和酚類物質的損失，通過積累更少的鈉和具有更多的光合色素和抗氧化活性來減輕鹽脅迫的負面影響（Salachna， Grzeszczuk & Mizielińska， 2019）。EPS 也是許多植物病原菌的毒力因數。此外，一些植物可以識別來自特定細菌的 EPS，這可以觸發水楊酸 （SA） 途徑並促進防禦基因的表達和 ROS 的產生（Milling et al.， 2011）。此外，EPS 和 CPS 的幾種純化組分具有眾所周知的誘導活性。 事實上，來自細菌細胞壁的 β-D-葡聚糖引起了植物防禦反應，例如幾丁質酶和苯丙氨酸解氨酶 （PAL） 活性的誘導以及異黃酮類化合物和植物抗毒素的合成（Chaliha 等人， 2018 年）。細菌果聚糖可以被認為是植物中的微生物相關分子模式 （MAMP），因為它們被果聚糖外水解酶水解產生低聚果糖 （FOS），從而啟動植物防禦（Versluys 等人， 2017 年）。黃原膠（圖 2）是細菌致病性的重要因素，可以通過改變過氧化物酶活性在某些植物物種中引發防禦機制（Luiz 等人， 2016 年）。鼠李糖還被證明可以誘導植物抗毒素的產生，包括巴戟天中的蒽醌（Doernenburg 和 Knorr，1994 ）。

2.1.2 Fungal polysaccharides
2.1.2 真菌多糖

The main fungal polysaccharides are α-D-Glucans, β-D-Glucans, chitin, and chitosan (Figures 1 and 3; Gorin and Barreto-bergter, 1983). α-D-Glucan polysaccharides in fungi are amylose, glycogen, pullulan, and mycodextran (Figure 1). Amylose classically occurs in plants as storage polysaccharides and can also be found in several species from Aspergillus, Bullera, Candida, Citeromyces, Cryptococcus, Fusicoccum, Penicillium, Rhodotorula, Tremella, to Trichosporon genera (Gorin and Barreto-bergter, 1983). Glycogen classically occurs in animals and several fungi species from Polyporus, Blastocladiella, or Trigonopsis genera (Gorin and Barreto-bergter, 1983; Coté et al., 2008). Pullulan is a linear homopolysaccharide of D-glucopyranose residues, containing 1 → 4 and 1 → 6 glycosidic linkages, produced by many species of the fungus Aureobasidium. Mycodextran is synthesized by fungi from Penicillium and Aspergillus species. Its structure consists of alternating 3- and 4-linked α-D-glucopyranosyl repeating units. β-D-glucans in fungi are cellulose and β-D-glucopyranans (Figure 1). Cellulose, classically occurring in higher plant cell walls, is also the skeletal component of the cell walls of Acrasiales, Oomycetes, and Hyphochytridiomycetes. The cell wall taxonomy of fungi is based on fungal cellulose content in combination with other glycomolecules (cellulose-glycogen, cellulose-β-D-glucan, or cellulose-chitin). β-D-glucopyranans with 1 → 6 and 1 → 3 linkages are found in Saccharomyces cervisiae and Candida species. Branched-chain β-D-glucopyranans are produced by fungi such as Aureobasidium pullulans, Sclerotium glucanicum, or Claviceps sp. (Gorin and Barreto-bergter, 1983; Coté et al., 2008).
主要的真菌多糖是 α-D-葡聚糖、β-D-葡聚糖、幾丁質和殼聚糖（圖 1 和 3;Gorin 和 Barreto-bergter，1983 年）。 真菌中的 α-D-葡聚糖多糖是直鏈澱粉、糖原、支鏈澱粉和菌原糖群（圖 1）。直鏈澱粉通常以儲存多糖的形式存在於植物中，也可以在幾個物種中找到，從曲黴屬 、Bullera、 念珠菌屬 、Citeromyces、Cryptococcus、Fusicoccum、 青黴屬 、Rhodotorula、Tremella 到毛孢菌屬（Gorin 和 Barreto-bergter，1983）。 糖原通常存在於動物和來自 Polyporus、Blastocladiella 或 Trigonopsis 屬的幾種真菌物種中（Gorin 和 Barreto-bergter，1983 年; Coté et al.， 2008）。普魯蘭多糖是 D-吡喃葡萄糖殘基的線性同多糖，包含 1 → 4 和 1 → 6 個糖苷鍵，由許多種類的真菌 Aureobasidium 產生。Mycodextran 由青霉屬和曲黴屬的真菌合成。其結構由交替的 3 和 4 α-D-吡喃葡萄糖重複單元組成。真菌中的 β-D-葡聚糖是纖維素和 β-D-吡喃葡萄糖（圖 1）。纖維素通常存在於較高的植物細胞壁中，也是 Acrasiales、Oomycetes 和 Hyphochytridiomycetes 細胞壁的骨骼成分。真菌的細胞壁分類學基於真菌纖維素含量與其他糖分子（纖維素-糖原、纖維素-β-D-葡聚糖或纖維素-幾丁質）的組合。 在鹿酵母菌屬和念珠菌屬中發現了具有 1 → 6 和 1 → 3 鍵的 β-D-吡喃葡萄糖。支鏈 β-D-吡喃葡萄糖由真菌產生，例如支鏈短梗霉 、 葡糖菌核或 Claviceps sp.（Gorin 和 Barreto-bergter，1983 年; Coté et al.， 2008）。

To the best of our knowledge, no studies have been devoted to fungal glucans as biostimulants. However, α-D-glucans from Laetiporus sulphureus have been found to stimulate wheat immunity by enhancing antioxidative activity, phenylpropanoids and lignin pathways, and pathogenesis-related (PR) protein synthesis (Nowak et al., 2022). Several other studies have shown the important role of fungal β-glucans in plant immunity (Chandrasekar et al., 2022; Fesel and Zuccaro, 2016).
據我們所知，還沒有專門研究將真菌葡聚糖作為生物刺激劑。然而，已發現來自 Laetiporus sulphureus 的 α-D-葡聚糖通過增強抗氧化活性、苯丙烷和木質素途徑以及發病機制相關 （PR） 蛋白質合成來刺激小麥免疫力（Nowak 等人， 2022 年）。其他幾項研究表明真菌 β-葡聚糖在植物免疫中的重要作用（Chandrasekar 等人， 2022 年;Fesel 和 Zuccaro，2016 年）。

Chitin is a linear polymer of β-(1 → 4)-linked 2-acetamido-2-deoxy-β-D-glucopyranosyl units found in many organisms such as filamentous fungi, yeasts, seaweeds, insects, worms, mollusks, and crustaceans (Figure 3). This analog of cellulose is found in several fungal genera like Boletus, Cantharellus, Aspergillus, Armillaria, Psalliota, Candida, and Saccharomyces. Chitosan, derived from chitin, is very similar to it, except that the N-acetyl-D-glucosamine is replaced by D-glucosamine, thus lacking N-acetyl groups (Figure 3). This polymer is present mainly in crustaceans and insects but can also be present in mycelia cell walls of certain fungi such as Phycomyces or Mucor genera (Coté et al., 2008).
甲殼素是 β-（1 → 4）-連接的 2-乙醯氨基-2-去氧-β-吡喃葡萄糖基單元的線性聚合物，存在於許多生物體中，如絲狀真菌、酵母、海藻、昆蟲、蠕蟲、軟體動物和甲殼類動物（圖 3）。這種纖維素類似物存在於幾個真菌屬中，如牛肝菌屬、Cantharellus、Aspergillus、Armillaria、Psalliota、Candida 和 Saccharomyces。殼聚糖來源於幾丁質，與殼聚糖非常相似，只是 N-乙醯-D-葡萄糖胺被 D-葡萄糖胺取代，因此缺乏 N-乙醯基（圖 3）。這種聚合物主要存在於甲殼類動物和昆蟲中，但也可以存在於某些真菌的菌絲體細胞壁中，例如 Phycomyces 或 Mucor 屬（Coté et al.， 2008）。

Chitosan was initially reported as an elicitor of plant immunity by inducing ROS (hydrogen peroxide), PR proteins, nitric oxide (NO), and phytoalexin accumulation. Similarly, chitin induces hypersensitive responses, mitogen-activated protein kinase (MAPK) pathways, PR proteins (such as chitinase), and PAL activities (Chaliha et al., 2018). In addition, several studies have also reported that chitosan has biostimulant activities, including protection against abiotic stresses and enhancement of plant growth, yield, nutrient uptake, microorganisms associated with plant roots, and shelf life of flowers and fruits. These activities were found on a large panel of plants like vegetables, ornamental plants, and fruit crops, using several application forms, including seed coating, foliar spraying, culture substrate incorporation, or as a coating agent for post-harvest protection (Pichyangkura and Chadchawan, 2015; Shahrajabian et al., 2021). Other studies have also been performed on chitin as a biostimulant. The main forms of chitin application are foliar spraying, culture substrate application, and coating products to induce the same biostimulant activities as chitosan (Shahrajabian et al., 2021).
殼聚糖最初被報導為通過誘導 ROS （過氧化氫）、PR 蛋白、一氧化氮 （NO） 和植物抗毒素積累而引發植物免疫的誘發劑。同樣，幾丁質誘導超敏反應、絲裂原活化蛋白激酶 （MAPK） 途徑、PR 蛋白（如幾丁質酶）和 PAL 活性（Chaliha 等人，2018 年）。此外，幾項研究還報告說，殼聚糖具有生物刺激素活性，包括防止非生物脅迫和促進植物生長、產量、養分吸收、與植物根相關的微生物以及花和水果的保質期。這些活動是在蔬菜、觀賞植物和水果作物等一大片植物上發現的，使用多種應用形式，包括種子包衣、葉面噴洒、培養基質摻入，或作為收穫后保護的塗層劑（Pichyangkura 和 Chadchawan，2015 年;Shahrajabian et al.， 2021）。還對幾丁質作為生物刺激劑進行了其他研究。甲殼素施用的主要形式是葉面噴施、培養基質施用和包衣產品，以誘導與殼聚糖相同的生物刺激劑活性（Shahrajabian et al.， 2021）。

2.1.3 Seaweed polysaccharides
2.1.3 海藻多糖

Seaweed polysaccharides can be categorized as cell wall constituents or storage materials. Major storage polysaccharides are laminaran and starch (Figure 1). Major cell wall structural components are cellulose, hemicellulose, alginate, ulvan, fucoidan, agar, carrageenan, and pectin (Goñi et al., 2020). The occurrence of these algal polysaccharides is highly dependent on taxa. Indeed, red algae are characterized by floridean starch, glucomannan, sulfated mixed-linkage glucan, agar, carrageenan, and porphyran. Brown algae are characterized by laminaran, sulfated xylofucoglucan, xylofucoglucuronan, alginate, and fucoidan. Green algae are characterized by xyloglucan, mannan, glucuronan, and sulfated glucuronoxylorhamnan (ulvan) (Popper et al., 2011).
海藻多糖可分為細胞壁成分或儲存材料。主要的貯藏多糖是海帶多糖和澱粉（圖 1）。主要的細胞壁結構成分是纖維素、半纖維素、海藻酸鹽、石蠟、岩藻多糖、瓊脂、角叉菜膠和果膠（Goñi 等人， 2020 年）。這些藻類多糖的出現高度依賴於分類群。事實上，紅藻的特徵是佛羅里達澱粉、葡甘露聚糖、硫酸化混合鍵葡聚糖、瓊脂、角叉菜膠和卟啉。褐藻的特徵是海帶糖、硫酸化木鹽葡聚糖、木鹽葡聚糖、藻酸鹽和岩藻多糖。綠藻的特徵是木葡聚糖、甘露聚糖、葡萄糖醛酸聚糖和硫酸化葡萄糖醛酸氧鹵漢聚糖 （ulvan） （Popper et al.， 2011）。

In storage polysaccharides, laminaran, also known as laminarin, is a glucan made up of glucose with β(1 → 3) linkages and β(1 → 6) or β(1 → 2) intrachain branching found in algae species such as Ecklonia kurome, Laminaria japonica, Laminaria digitata, and Eisenia bicyclis (Figure 1; Olatunji, 2020). Laminaran is very well known to elicit plant-defense responses such as phytoalexin, ROS, cytosolic Ca²⁺influx, PR protein inductions, gene expressions of the SA signaling pathway, pattern-triggered immunity markers and transcription factors (Goñi et al., 2020; Wu et al., 2016; Mirande-Ney et al., 2023). It was also demonstrated to have biostimulant activities. Indeed, included in the culture substrate of Arabidopsis thaliana (L.) Heynh., laminaran promotes plant growth and tolerance to heat and salt stresses by regulating the defensin-like protein (DEFL) mediated pathways (Wu et al., 2016). A patent from Yvin et al., (1998) claims that this seaweed β-glucan improves seed germination of carrots (Daucus carota subsp. sativus (Hoffm.) Schübl. & G. Martens), lettuce (Lactuca sativa L.), and chicory (Cichorium intybus var. foliosum Hegi) when applied in the growth medium and enhances elongation of wheat coleoptiles (Triticum aestivum L.) after foliar spray. Carrasco-Gil et al., (2021) also showed that laminaran treatments enhanced seed germination and increased the root length of tomatoes (Solanum lycopersicum L.).
在儲存多糖中，海帶多糖，也稱為海帶多糖，是一種由葡萄糖組成的葡聚糖，具有 β（1 → 3） 鍵和 β（1 → 6） 或 β（1 → 2） 鏈內支鏈，存在於 Ecklonia kurome、Laminaria japonica、Laminaria digitata 和 Eisenia bicyclis 等藻類物種中（圖 1;Olatunji，2020 年）。眾所周知，海帶多糖可以引發植物防禦反應，例如植物抗毒素、ROS、胞質 Ca²⁺ 內流、PR 蛋白誘導、SA 信號通路的基因表達、模式觸發的免疫標誌物和轉錄因數（Goñi 等人， 2020 年;Wu et al.， 2016;Mirande-Ney et al.， 2023）。它還被證明具有生物刺激素活性。事實上，包含在擬南芥 （L.） Heynh. 的培養基質中，海帶多糖通過調節防禦素樣蛋白 （DEFL） 介導的途徑促進植物生長和對熱和鹽脅迫的耐受性（Wu 等人， 2016 年）。Yvin 等人 （1998） 的一項專利聲稱這種海藻 β-葡聚糖可以改善胡蘿蔔 （Daucus carota subsp. sativus （Hoffm.）舒布爾。& G. Martens）、生菜（Lactuca sativa L.）和菊苣（Cichorium intybus var. foliosum Hegi）在生長培養基中施用時，可以增強小麥胚芽鞘（Triticum aestivum L.）在葉面噴施后的伸長。Carrasco-Gil 等人（2021 年）還表明，海帶處理促進了種子發芽並增加了西紅柿 （Solanum lycopersicum L.） 的根長。

Starch is the principal energy-storage carbohydrate of plants and an end product of photosynthesis. It is composed of two polymers: amylose and amylopectin (Figure 1). Amylose consists of a linear chain of α-(1 → 4)-D-glucose units, and amylopectin is also composed of α-(1 → 4)-D-glucose units but branched with α-(1 → 6) linkages. This major energy-storage carbohydrate occurs naturally in higher plants but is also present in red, brown, and green macroalgae and microalgae (Olatunji, 2020). Starch is also an essential substance in plant responses to abiotic stresses, such as water deficit and high salinity. Indeed, under challenging environmental conditions, aquatic and land plants generally remobilize starch to provide energy and carbon at times when photosynthesis becomes limited (Dong and Beckles, 2019). It is, therefore, used for many species as an acclimation strategy in harsh environments. Starch from algal origin has several applications, including in the textile, food, biomedical, pharmaceutical, and energy industries (Olatunji, 2020), but to date, no biostimulant or elicitor activities have been reported.
澱粉是植物的主要能量儲存碳水化合物，也是光合作用的最終產品。它由兩種聚合物組成：直鏈澱粉和支鏈澱粉（圖 1）。直鏈澱粉由 α-（1 → 4）-D-葡萄糖單元的線性鏈組成，支鏈澱粉也由 α-（1 → 4）-D-葡萄糖單元組成，但以 α-（1 → 6） 鍵支鏈。這種主要的能量儲存碳水化合物天然存在於高等植物中，但也存在於紅色、棕色和綠色的大型藻類和微藻中（Olatunji，2020 年）。澱粉也是植物應對非生物脅迫（如水分短缺和高鹽度）的必需物質。事實上，在具有挑戰性的環境條件下，水生和陸地植物通常會在光合作用受到限制時重新動員澱粉以提供能量和碳（Dong 和 Beckles，2019 ）。因此，它被許多物種用作惡劣環境中的馴化策略。藻類來源的澱粉有多種應用，包括紡織、食品、生物醫學、製藥和能源行業（Olatunji，2020 年），但迄今為止，尚未報導生物刺激劑或引發劑活性。

Alginate is the main polysaccharide found in the cell walls of brown seaweeds. It is a linear anionic polysaccharide, which consists of binary copolymers of the uronic acids β-D-mannuronic acid (M) and α-L-guluronic acid (G) units bound via β-(1 → 4) or α-(1 → 4) linkages (Figure 4).
海藻酸鹽是在棕色海藻的細胞壁中發現的主要多糖。它是一種線性陰離子多糖，由糖醛酸 β-D-甘露糖醛酸 （M） 和 α-L-古糖醛酸 （G） 單元的二元共聚物組成，通過 β-（1 → 4） 或 α-（1 → 4） 鍵結合（圖 4）。

Several studies have suggested that alginates and oligo-alginates induce resistance against plant pathogens such as viruses, bacteria, and fungi by blocking viral proteins, activate defense-related genes, e.g., PAL, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO), chitinase (CHI), and glucanase; or increase ROS, NO, flavonoids, and phytoalexin contents (Riseh et al., 2022). In addition, other studies have shown their biostimulant activities (Goñi et al., 2020). Indeed, foliar spraying of alginate oligosaccharides enhanced wheat (T. aestivum; Liu et al., 2013) and cucumber (Cucumis sativus L.; Li et al., 2018) tolerance to drought stress. Further, bulb coating limits the negative effects of salinity stress of umathunga (Eucomis autumnalis (Mill) Chitt; Salachna et al., 2018a). Moreover, seed coating was shown to enhance wheat tolerance to cadmium by increasing root and shoot lengths, fresh and dry weight, chlorophyll content, and antioxidant enzyme activities (SOD, CAT, and POD; Ma et al., 2010). Alginate-derived oligosaccharides with low molecular weights around 500–3000 Da and a higher ratio of mannuronate to guluronate (M/G ratios >1; indicating a lower viscosity) applied by coating on barley seeds (Hordeum vulgare L.) stimulated the growth of seedlings and roots, photosynthetic activity, and expression of development and stress tolerance-related genes like auxin response factor and MAPK (Yang et al., 2020). Some studies have shown that this oligoalginate, included in the culture medium, stimulated seed germination and increased the root length of lettuce (L. sativa) (Iwasaki and Matsubara, 2000) carrots (D. carota subsp. sativus), rice (Oryza sativa L.;Xu et al., 2003), maize (Zea mays L.; Hu et al., 2004), and tomatoes (S. lycopersicum; Carrasco-Gil et al., 2021).
幾項研究表明，藻酸鹽和寡藻酸鹽通過阻斷病毒蛋白、啟動防禦相關基因，例如 PAL、超氧化物歧化酶 （SOD）、過氧化氫酶 （CAT）、過氧化物酶 （POD）、多酚氧化酶 （PPO）、幾丁質酶 （CHI） 和葡聚糖酶;或增加 ROS、NO、類黃酮和植物抗毒素含量（Riseh et al.， 2022）。此外，其他研究表明了它們的生物刺激劑活性（Goñi 等， 2020）。事實上，葉面噴施海藻酸鹽低聚糖增強了小麥（T. aestivum;Liu et al.， 2013） 和黃瓜 （Cucumis sativus L.;Li et al.， 2018） 對乾旱脅迫的耐受性。此外，鱗莖塗層限制了 umathunga （Eucomis autumnalis （Mill） Chitt;Salachna 等人， 2018a）。此外，種子包衣通過增加根和芽長度、鮮重和乾重、葉綠素含量和抗氧化酶活性（SOD、CAT 和 POD;馬等人， 2010 年）。海藻酸鹽衍生的低聚糖分子量約為 500-3000 Da，甘露糖醛酸與谷胱醛酸的比例較高（M/G 比值 >1;表明粘度較低），通過塗覆在大麥種子 （Hordeum vulgare L.） 上，刺激幼苗和根的生長、光合活性以及發育和脅迫耐受性相關基因（如生長素回應因數和 MAPK）的表達（Yang 等人， 2020 年）。 一些研究表明，培養基中包含的這種低聚藻酸鹽刺激種子發芽並增加生菜 （L. sativa） （Iwasaki 和 Matsubara， 2000） 胡蘿蔔 （D. carota subsp. sativus）、水稻 （Oryza sativa L.;Xu et al.， 2003）、玉米 （Zea mays L.;胡等人， 2004 年）和西紅柿（S. lycopersicum;Carrasco-Gil et al.， 2021）。

Ulvans are sulfated heteropolysaccharides of green algae cell walls, especially in Ulva and Enteromorpha sp. They are composed of rhamnose (Rha; 17%–45%). Their structures consist of two main repeating disaccharides: the ulvabiuronic acid type A (β-D-GlcA (1 → 4) α-L-Rha 3S → 1) and type B (α-L-IdoA (1 → 4) α-L-Rha 3S → 1; Robic et al., 2008; Figure 4).
Ulvans 是綠藻細胞壁的硫酸化雜多糖，尤其是在 Ulva 和 Enteromorpha 屬中。它們由鼠李糖 （Rha;17%–45%） 組成。它們的結構由兩種主要的重複二糖組成：A 型 （β-D-GlcA （1 → 4） α-L-Rha 3S → 1） 和 B 型 （α-L-IdoA （1 → 4） α-L-Rha 3S → 1;Robic et al.， 2008;圖 4）。

Several studies have used ulvan extracts as elicitors of plant immunity against various pathogens. Applied on several plants, they have been shown to enhance the expression of defense-related genes, the biosynthesis of phytoalexins, the amplification of oxidative bursts, and the activation of the jasmonic acid (JA) signaling pathway and antioxidant-related enzymes (Goñi et al., 2020). For biostimulant activities, ulvan-enriched extracts obtained from Ulva lactuca promoted seed germination and stimulated growth and rooting of tomato (S. lycopersicum) and mung bean plants (Vigna radiata (L.) R. Wilczek; Hernández-Herrera et al., 2016). Moreover, ulvans applied by foliar spraying or included in the growth or culture medium induced genes involved in nitrogen absorption of Medicago truncatula Gaertn., a significant effect on mineral nitrogen absorption in wheat (T. aestivum), and increased protein content in peas (P. sativum) and maize (Z. mays; Briand et al., 2011). In terms of abiotic stress tolerance, ulvans applied to the leaves or roots of maize enhanced the plant biomass under heat and drought stresses (Goñi et al., 2020). More recently, Shefer et al., (2022) showed that ulvans extracted from cultivated green algae Ulva sp. and added to the growth medium stimulated length and weight of roots, shoots, and total plants of A. thaliana.
一些研究使用石蒓提取物作為植物對各種病原體免疫的誘因。應用於多種植物，它們已被證明可以增強防禦相關基因的表達、植物抗毒素的生物合成、氧化爆發的放大以及茉莉酸 （JA） 信號通路和抗氧化相關酶的啟動（Goñi 等人，2020 年）。對於生物刺激劑活性，從石莼中獲得的富含石蓴的提取物促進種子發芽，並刺激番茄 （S. lycopersicum） 和綠豆植物 （Vigna radiata （L.） R. Wilczek;Hernández-Herrera et al.， 2016）。此外，葉面噴施或包含在生長或培養基中的石莼誘導了參與苜蓿 Gaertn. 氮吸收的基因，對小麥 （T. aestivum） 的礦物氮吸收有顯著影響，並增加了豌豆 （P. sativum） 和玉米 （Z. mays;Briand et al.， 2011）。在非生物脅迫耐受性方面，應用於玉米葉或根的石莼在高溫和乾旱脅迫下提高了植物生物量（Goñi et al.， 2020）。最近，Shefer 等人（2022 年）表明，從培養的綠藻石蓴屬中提取的石蓴並添加到生長培養基中刺激了擬南芥根、芽和總植物的長度和重量。

Fucoidans or algal fucans are composed of sulfated α-L-fucose backbones with small amounts of other monosaccharides, including D-glucose, D-galactose, D-mannose, D-xylose, D-glucuronic acid, and acetyl groups (Figure 4).
岩藻糖膠或藻類岩藻糖由硫酸化的 α-L-岩藻糖骨架和少量其他單糖組成，包括 D-葡萄糖、D-半乳糖、D-甘露糖、D-木糖、D-葡萄糖醛酸和乙醯基（圖 4）。

Fucoidans have been identified with a range of bioactive properties, which give them potential applicability in the food, cosmetics, pharmaceutical, and biomedical industries (Olatunji, 2020). In agricultural applications, several studies have investigated the elicitation of plant defense against phytopathogens (Goñi et al., 2020). These studies reported the release of H₂O, stimulation of PAL, lipoxygenase (LOX), and glutathione S-transferase (GST) enzymes, and the accumulation of SA, phytoalexins, and PR proteins (Goñi et al., 2020). However, only one study reported a biostimulant activity of fucoidans from Macrocystis pyrifera, which were shown to induce plant resistance to salt stress in wheat when applied by foliar spray (T. aestivum; Zou et al., 2021).
褐藻糖膠已被確定具有一系列生物活性特性，這使它們在食品、化妝品、製藥和生物醫學行業具有潛在的適用性（Olatunji，2020 年）。在農業應用中，一些研究調查了植物對植物病原體的防禦（Goñi 等人， 2020 年）。這些研究報告了 H₂O 的釋放、PAL 、脂氧合酶 （LOX） 和谷胱甘肽 S-轉移酶 （GST） 酶的刺激，以及 SA、植物抗毒素和 PR 蛋白的積累（Goñi 等人， 2020 年）。然而，只有一項研究報告了來自大藻糖的岩藻糖膠的生物刺激劑活性，當葉面噴施時，這些岩藻糖膠被證明可以誘導小麥植物對鹽脅迫的抵抗力（T. aestivum;Zou 等人， 2021 年）。

Carrageenans, sulfated galactans, are linear polysaccharides composed of repeating dimers of D-galactose, which are linked via alternated bonds of α-1,3 and β-1,4 and substituted by one (κ-carrageenan), two (ι-carrageenan), or three (λ-carrageenan) sulfate ester groups within each repeating unit (Figure 5).
角叉菜膠，硫酸化半乳聚糖，是由 D-半乳糖的重複二聚體組成的線性多糖，它們通過 α-1,3 和 β-1,4 的交替鍵連接，並被每個重複單元內的一個（κ-角叉菜膠）、兩個（ι-角叉菜膠）或三個（λ-角叉菜膠）硫酸酯基團取代（圖 5）。

Carrageenans and oligo-carrageenans facilitate plant growth through several metabolic processes, including chlorophyll metabolism, carbon fixation, photosynthesis, protein synthesis, secondary metabolite generation, and detoxification of ROS. In parallel, these compounds suppress pathogens by their direct antimicrobial activities and improve plant resilience against pathogens by modulating biochemical changes via SA and JA and ethylene (ET) signaling pathways, resulting in increased production of secondary metabolites, defense-related proteins, and antioxidants.
角叉菜膠和寡角叉菜膠通過多種代謝過程促進植物生長，包括葉綠素代謝、碳固定、光合作用、蛋白質合成、次生代謝物生成和 ROS 的解毒。同時，這些化合物通過其直接的抗菌活性抑制病原體，並通過 SA 和 JA 以及乙烯 （ET） 信號通路調節生化變化來提高植物對病原體的抵抗力，從而增加次生代謝物、防禦相關蛋白質和抗氧化劑的產生。

Carrageenans are known to induce plant-defense responses against viruses, viroids, bacteria, fungi, and insects by stimulating JA, SA, and ET signaling pathways (Goñi et al., 2020; Mukarram et al., 2021). However, when (κ, ι, or λ)-carrageenans were applied via seed coating and foliar spraying, several other studies have demonstrated biostimulant activities on quality traits of various plants, including V. radiata, Foeniculum vulgare Mill., Cicer arietinum L., Z. mays, Eucalyptus globulus Labill., Arachis hypogaea L., Nicotiana tabacum L., Ocimum basilicum L. The application of these carrageenans also enhanced nutrient efficiency in Pinus radiata D. Don and enhanced drought stress tolerance in Cymbopogon flexuosus Steud (Goñi et al., 2020; Hossain et al., 2024; Mukarram et al., 2021).
已知角叉菜膠通過刺激 JA、SA 和 ET 信號通路誘導植物對病毒、類病毒、細菌、真菌和昆蟲的防禦反應（Goñi 等人，2020 年;Mukarram et al.， 2021）。然而，當通過種子包衣和葉面噴施施用（κ、ι或λ）-角叉菜膠時，其他幾項研究已經證明瞭生物刺激劑對各種植物的品質性狀有活性，包括輻射蒲公英 、Foeniculum vulgare Mill.、Cicer arietinum L.、Z. mays、Eucalyptus globulus Labill.、Arachis hypogaea L.、Nicotiana tabacum L.、Ocimum basiliumL.這些角叉菜膠的應用還提高了 Pinus radiata D. Don 的營養效率，並增強了 Cymbopogon flexuosus Steud 的乾旱脅迫耐受性（Goñi 等人， 2020 年;Hossain et al.， 2024;Mukarram et al.， 2021）。

Agar is a mixture of two polymers, agarose and agaropectin. Agarose is a neutral linear polymer consisting of 3-O substitute β-D-galactopyranosyl and 3,6-anhydro-α-L-galactopyranosyl repeating units, while agaropectin is charged with sulfate groups (Figure 5). Agar is a well-established biopolymer obtained from red algae, mainly from Gracilaria sp. and Gelidium sp., which has diverse applications in the food, biotechnology, cosmetics, and pharmaceutical industries (Olatunji, 2020). There is still a lack of studies regarding agricultural utilization of agar. To the best of our knowledge, no study has dealt with plant-defense responses on land plants. Only a few studies on macroalgae have shown the plant-defense activities of agar and oligo-agar. Oligo-agar applied in seawater medium elicited a response in the red alga Pyropia haitanensis T.J. Chang & B.F. Zheng by reducing the rotting rate of the algae, enhancing oxidative bursts, increasing volatile organic compounds, phospholipase A2 activity, and decreasing free fatty acid contents (Wang et al., 2013). Gracilaria sp. also responded by enhancing oxidative bursts with hydrogen peroxide when oligo-agars were added to the medium (Weinberger et al., 2005, 2010).
瓊脂是瓊脂糖和瓊脂糖蛋白兩種聚合物的混合物。瓊脂糖是一種中性線性聚合物，由 3-O 取代 β-D-吡喃半乳糖基和 3,6-脫水-α-L-吡喃半乳糖基重複單元組成，而瓊脂糖素則帶有硫酸鹽基團電荷（圖 5）。瓊脂是一種從紅藻中提取的成熟生物聚合物，主要來自 Gracilaria sp. 和 Gelidium sp.，在食品、生物技術、化妝品和製藥行業有多種應用（Olatunji，2020 年）。 仍然缺乏關於瓊脂農業利用的研究。據我們所知，還沒有研究涉及陸地植物的植物防禦反應。只有少數關於大型藻類的研究顯示了瓊脂和低聚瓊脂的植物防禦活性。在海水介質中施用寡聚瓊脂在紅藻 Pyropia haitanensis T.J. Chang & B.F. Zheng 通過降低藻類的腐爛速度、增強氧化爆發、增加揮發性有機化合物、磷脂酶 A2 活性和降低遊離脂肪酸含量（Wang 等人， 2013）中引起了反應。當向培養基中加入寡聚瓊脂時，Gracilaria sp. 還通過增強過氧化氫的氧化爆發來回應（Weinberger 等人， 2005 年，2010 年）。

As for biostimulant activities, a study showed that agar extracted from the red seaweed G. gracilis applied in the culture medium improved the growth and seed germination of Brassica oleracea L. (Pacheco et al., 2021). Another study indicated that agar promoted the growth of Amaranthus viridis L. when applied to soil under drought stress conditions (Mahusook et al., 2021). This observation aligns with the recent review on natural superabsorbent glycopolymers, such as agarose, cellulose, starch, and alginate, as water-saving products and soil conditioners in agriculture because of their water-retention properties (Behera and Mahanwar, 2019).
至於生物刺激劑活性，一項研究表明，從紅海藻中提取的瓊脂應用於培養基中，改善了 Brassica oleracea L. 的生長和種子發芽（Pacheco et al.， 2021）。另一項研究表明，在乾旱脅迫條件下施用到土壤時，瓊脂促進了 Amaranthus viridis L. 的生長（Mahusook et al.， 2021）。這一觀察結果與最近對天然高吸水性糖聚合物（如瓊脂糖、纖維素、澱粉和藻酸鹽）的評論一致，因為它們具有保水特性，因此在農業中用作節水產品和土壤改良劑（Behera 和 Mahanwar，2019 年）。

Porphyran and oligo-porphyran (Figure 5) have a wide range of applications in medicine, cosmetics, and food due to their antioxidant, immune-modulating, anti-aging, and antimicrobial activities (Wang et al., 2023). But to date, no agricultural application has been reported.
卟啉和寡卟啉（圖 5）由於其抗氧化、免疫調節、抗衰老和抗菌活性，在醫學、化妝品和食品中具有廣泛的應用（Wang et al.， 2023）。但迄今為止，尚未報告農業應用。

Cellulose, pectins, and hemicelluloses are polysaccharides shared with land plants. Algae sources of cellulose include red, brown, and green macroalgae. Cellulose is a linear polymer made up of chains of β-(1 → 4)-linked glucose residues (Olatunji, 2020; Figure 1). Hemicelluloses and their analogs also are found in the cell walls of green, red, and brown seaweeds (Figure 6). Pectin is typically found in land-plant cell walls (Figure 7). But some forms of pectins are also found in macroalgae and marine diatoms (Arnosti et al., 2021; Vidal-Melgosa et al., 2021).
纖維素、果膠和半纖維素是與陸地植物共用的多糖。纖維素的藻類來源包括紅色、棕色和綠色大型藻類。纖維素是一種線性聚合物，由 β-（1 → 4） -連接的葡萄糖殘基鏈組成（Olatunji，2020 年;圖 1）。半纖維素及其類似物也存在於綠色、紅色和棕色海藻的細胞壁中（圖 6）。果膠通常存在於陸地植物細胞壁中（圖 7）。但某些形式的果膠也存在於大型藻類和海洋矽藻中（Arnosti 等人， 2021 年;Vidal-Melgosa 等人， 2021 年）。

Cellulose, pectins, and hemicelluloses from algae seemed to have no research reports available on their agricultural applications even though they are widely studied for bioethanol production, preparation of paper, nano and microcrystalline polymers, or bioplastics (Baghel et al., 2021).
藻類中的纖維素、果膠和半纖維素似乎沒有關於其農業應用的研究報告，儘管它們被廣泛研究用於生物乙醇生產、紙張製備、納米和微晶聚合物或生物塑膠（Baghel 等人，2021 年）。

2.1.4 Microalgae  2.1.4 微藻

Polysaccharide extracts of Chlorella vulgaris coated on seeds of wheat (Triticum vulgare L.) and French beans (Phaseolus vulgaris L.) increased their growth parameters, including dry and fresh weights, leaf area, shoot height, and root length, photosynthetic pigment carbohydrate and protein contents, and antioxidant activities in seedling leaves. The polysaccharide extract used contained six monosaccharide and disaccharide units, fructose, glucose, maltose, lactose, rhamnose, and arabinose in addition to other components like sulphate, uronic acids, and proteins (El-Naggar et al., 2020).
小麥 （Triticum vulgare L.） 和菜豆 （Phaseolus vulgaris L.） 種子包衣的常溫小球藻多糖提取物提高了其生長參數，包括苗葉干重和鮮重、葉面積、芽高和根長、光合色素碳水化合物和蛋白質含量以及抗氧化活性。使用的多糖提取物含有六個單糖和二糖單元、果糖、葡萄糖、麥芽糖、乳糖、鼠李糖和阿拉伯糖，以及硫酸鹽、糖醛酸和蛋白質等其他成分（El-Naggar 等人， 2020 年）。

Exopolysaccharide extracts of Dunaliella salina, containing 46.9% neutral sugars, 8.3% uronic acids, and 2.8% sulfate groups, applied on S. lycopersicum by foliar spraying increased plant growth, balanced K⁺/Na⁺ ratios, and induced very long-chain fatty acid (VLCFA) biosynthesis involved in the wax construction in salt stress conditions (El Arroussi et al., 2018).
杜氏鹽藻的胞外多糖提取物含有 46.9% 的中性糖、8.3% 的糖醛酸和 2.8% 的硫酸鹽基團，通過葉面噴施在 S. lycopersicum 上，促進了植物生長，平衡了 K⁺/Na⁺ 比率，並誘導了非常長鏈脂肪酸 （VLCFA） 生物合成，參與鹽脅迫條件下的蠟構建（El Arroussi et al.， 2018）。

2.1.5 Land-plant polysaccharides
2.1.5 陸地植物多糖

As seaweeds and marine grasses, land plants have polysaccharides for energy-storage and cell-wall composition. Major energy-storage glycomolecules are starch, fructan, galactan, galactomannan, and glucomannan. Starch (Figure 1) is a major energy-storage carbohydrate implicated in plant stress mitigation by remobilising its reserves to release energy, sugars and derived metabolites.(Dong et al. 2019; see also Section 1.1.3). However, no study has reported the use of land-plant starch as a biostimulant. Though, some agricultural applications have explored its use as a pesticide or a fertilizer-delivery system and as a natural superabsorbent glycopolymer to preserve soil moisture (Das et al. 2020). Similarly, very few studies have mentioned its elicitor activities. Soluble starch from potatoes applied in culture growths of different Hypericum species showed an increase of several phenolics like kaempferol-3-O-glucoside, chlorogenic acid, catechin, rutin, amentoflavone, and phloroglucinol (Bálintová et al., 2019).
與海藻和海草一樣，陸地植物具有用於能量儲存和細胞壁組成的多糖。主要的能量存儲糖分子是澱粉、果聚糖、半乳聚糖、半乳甘露聚糖和葡甘露聚糖。澱粉（圖 1）是一種主要的能量儲存碳水化合物，通過重新動員其儲備以釋放能量、糖和衍生代謝物，與緩解植物壓力有關。（Dong 等人， 2019 年;另見第 1.1.3 節 ）。 然而，沒有研究報導使用陸地植物澱粉作為生物刺激劑。不過，一些農業應用已經探索了它作為殺蟲劑或肥料輸送系統以及作為天然高吸水性糖聚合物的用途來保持土壤水分（Das 等人，2020 年）。同樣，很少有研究提到它的誘發活性。用於不同金絲桃物種培養生長的馬鈴薯可溶性澱粉顯示幾種酚類物質的增加，如山奈酚-3-O-葡萄糖苷、 綠原酸、兒茶素、蘆丁、薄荷黃酮和間苯三酚（Bálintová等人， 2019 年）。

Three types of fructans exist: inulin, graminan, and levan (Figure 8), comprised of β-D-fructose units. Levan is also an exopolysaccharide produced by bacteria (see Section 2.1.1). Different types of fructans are found in plants depending on the linkage type and branching (Figure 8), including inulins (β-2,1-fructosyl bonds), levans (β-2,6-fructosyl bonds), graminans (mix of β-2,1 and β-2,6-fructosyl bonds), and neokestose-type inulins and levans as well as complex, mixed-type fructans (agavin; Versluys et al., 2017). Fructans have either β-2,1 (inulin), β-2,6 (levan), or a mix of both (graminan) glycosidic bonds (Figure 8). Dicot plants mainly produce inulin while levan, mixed-type fructans (graminans) and neokestose-based fructans are mostly found in monocots (Versluys et al., 2017). Aside from their energy-storage functions, they are associated with stress-tolerance mechanisms, such as freezing and drought stress, and as osmoprotectants. However, despite this osmoprotective activity, we have not found any report on the use of these compounds as biostimulants (Jiménez-Arias et al., 2021). Several studies have highlighted their action as elicitors of plant defense against phytopathogens (Versluys et al., 2017). Indeed, inulin, levan, or fructooligosaccharides improved plant resistance to infection in A. thaliana, L. sativa, S. lycopersicum, Vitis labrusca L., Malus domestica Borkh., and C. sativus (Versluys et al., 2017; Janse van Rensburg et al., 2020).
存在三種類型的果聚糖：菊粉、禾谷多糖和萊萬（圖 8），由 β-D-果糖單元組成。Levan 也是細菌產生的胞外多糖（參見第 2.1.1 節 ）。根據鍵型和支化，在植物中發現了不同類型的果聚糖（圖 8），包括菊粉（β-2,1-果糖基鍵）、levans（β-2,6-果糖基鍵）、禾谷多糖（β-2,1 和 β-2,6-果糖基鍵的混合物）和新糖型菊粉和 levans，以及複雜的混合型果聚糖（agavin;Versluys 等人， 2017 年）。果聚糖具有 β-2,1（菊粉）、β-2,6（levan）或兩者（禾谷多糖）糖苷鍵的混合物（圖 8）。雙子葉植物主要生產菊粉，而 levan、混合型果聚糖（禾谷聚糖）和基於新酮的果聚糖主要存在於單子葉植物中（Versluys 等人， 2017 年）。除了它們的能量儲存功能外，它們還與耐壓機制（如凍結和乾旱脅迫）有關，並作為滲透保護劑。然而，儘管具有這種滲透保護活性，我們還沒有找到任何關於使用這些化合物作為生物刺激劑的報告（Jiménez-Arias et al.， 2021）。幾項研究強調了它們作為植物防禦植物病原體的誘因（Versluys et al.， 2017）。事實上，菊粉、levan 或低聚果糖提高了植物對擬南芥 、 苜蓿 、 石松石蒜、Vitis labrusca L.、Malus domestica Borkh. 和 C. sativus 的感染抵抗力（Versluys 等人， 2017 年;Janse van Rensburg et al.， 2020）。

Fructans are also present in bacteria (see Section 1.1.1) and fungi (see Section 1.1.3). Interestingly, Versluys et al., (2017), Versluys and Van 2022) have proposed a potential role of microbial fructans as MAMP and plant fructans as DAMP giving them a priming status to future biotic and abiotic stress management. Inulin from chicory roots can trigger Arabidopsis resistance against Botrytis cinerea by increasing H₂O₂, ROS-scavenging enzymes, NADPH-oxidase, and sugar content (Janse van Rensburg et al., 2020).
果聚糖也存在於細菌（參見第 1.1.1 節）和真菌（參見第 1.1.3 節  ）中。有趣的是，Versluys 等人（2017 年）、Versluys 和 Van 2022 年）提出了微生物果聚糖作為 MAMP 和植物果聚糖作為 DAMP 的潛在作用，使它們為未來的生物和非生物脅迫管理奠定了基礎。菊苣根中的菊粉可以通過增加 H₂O₂、ROS 清除酶、NADPH 氧化酶和糖含量來觸發擬南芥對灰葡萄孢菌的抗性（Janse van Rensburg 等人， 2020 年）。

Other energy-storage polysaccharides include cell-wall polysaccharides such as pectins and hemicelluloses e.g. galactomanan and glucomannan.
其他儲能多糖包括細胞壁多糖（如果膠）和半纖維素（如半乳糖聚糖和葡甘露聚糖）。

The cell wall plays a role in the growth, differentiation, mechanical integrity, and interface between cells and the environment (Somerville, 2004). Cell-wall polysaccharides are cellulose, hemicelluloses, and pectins. Hemicellulose and pectins are assembled in the Golgi apparatus and then transported via Golgi-derived vesicles to the cell wall. By contrast, cellulose is synthesized at the plasma membrane. Together, hemicelluloses and pectins constitute the matrix in which cellulose microfibrils are embedded. In both primary and secondary cell walls, cellulose, hemicelluloses, and pectins are mixed, and the interactions among the different polysaccharides ensure both strength and flexibility of the cell wall (Somerville, 2004).
細胞壁在細胞與環境之間的生長、分化、機械完整性和介面中發揮作用 （Somerville， 2004）。細胞壁多糖是纖維素、半纖維素和果膠。半纖維素和果膠在高爾基體中組裝，然後通過高爾基體衍生的囊泡運輸到細胞壁。相比之下，纖維素是在質膜上合成的。半纖維素和果膠共同構成了纖維素微纖維嵌入其中的基質。在初級和次級細胞壁中，纖維素、半纖維素和果膠混合在一起，不同多糖之間的相互作用確保了細胞壁的強度和柔韌性（Somerville，2004）。

Cellulose is the most abundant cell wall component among the polysaccharides with 30–70% of the cell wall composition. It occurs in all higher plants and some algae, fungi, bacteria, and certain animals like truncates and protozoans. It is a linear homopolysaccharide (Figure 1; see also Section 2.1.3) forming six long and rigid microfibrils, organized in six macrofibrils, synthesized by cellulose synthase complexes and delivered to the plasma membrane (Anderson and Kieber, 2020).
纖維素是多糖中最豐富的細胞壁成分，占細胞壁成分的 30-70%。它存在於所有高等植物和一些藻類、真菌、細菌和某些動物中，如截肢動物和原生動物。它是一種線性同多糖（圖 1;另見第 2.1.3 節 ），形成六個長而剛性的小原纖維，由六個大原纖維組織，由纖維素合酶複合物合成並遞送到質膜（Anderson 和 Kieber，2020 年）。

Cellulose from land plants has numerous applications in various industrial fields such as the manufacturing of paper and cardboard, textiles, pharmaceuticals, biofuels, and food (Gupta et al., 2019). Recent studies on agricultural applications have explored cellulose's potential in holding water and water-soluble fertilizers in the soil (Das et al., 2020; França et al., 2021).
陸地植物中的纖維素在各個工業領域都有廣泛的應用，例如紙張和紙板的製造、紡織品、製藥、生物燃料和食品（Gupta 等人，2019 年）。最近關於農業應用的研究探索了纖維素在土壤中保持水分和水溶性肥料的潛力（Das 等人，2020 年;França 等人， 2021 年）。

To the best of our knowledge, very few studies have been carried out on the biostimulant activities of cellulose. The application of this polysaccharide in the soil of O. sativa influenced rhizosphere enzymatic activities under phosphorus fertilization (Wei et al., 2019). Cellobiose, a dimer of cellulose (Figure 1), was shown to increase fresh weight of A. thaliana seedlings when applied in high concentrations in the culture medium (Souza et al., 2017). Moreover, oligomers of cellulose have been reported as DAMPs in plant immunity. Aziz et al., (2007) were able to induce defense responses in Vitis vinifera L. including oxidative bursts, elevation of free cytosolic Ca²⁺, and the expression of PR genes. Souza et al., (2017) also showed that cellobiose applied to Arabidopsis seedlings induced overexpression of WRKY transcription factor genes, triggered early Ca²⁺ transient, and activated MAPKs signaling cascade and suberin biosynthesis.
據我們所知，關於纖維素的生物刺激劑活性的研究很少。這種多糖在 O. same 土壤中的應用影響了磷施肥下的根際酶活性（Wei et al.， 2019）。纖維二糖是纖維素的二聚體（圖 1），當在培養基中以高濃度施用時，纖維二糖可以增加擬南芥幼苗的鮮重（Souza 等人， 2017 年）。此外，據報導，纖維素的低聚物在植物免疫中是 DAMP。Aziz et al.， （2007） 能夠在 Vitis vinifera L. 中誘導防禦反應，包括氧化爆發、遊離胞質 Ca²⁺ 的升高和 PR 基因的表達。Souza et al.， （2017） 還表明，應用於擬南芥幼苗的纖維二糖誘導 WRKY 轉錄因數基因的過表達，觸發早期 Ca²⁺ 暫態，並啟動 MAPKs 信號級聯和軟木素生物合成。

Hemicellulose, ca. 20–40% of the cell wall, and cellulose are structurally related compounds (see also Section 2.1.3) and are closely associated in the cell wall. Both of these heteropolysaccharides are characterized by a backbone of β-1,4-linked sugars and are grouped into three classes: (1) glucans like xyloglucan and β-glucan, (2) xylans like xylan and arabinoxylan, and (3) mannans like glucomannan and galactoglucomannan (Scheller and Ulvskov, 2010). Xyloglucans are the most abundant hemicelluloses in the primary cell walls of eudicots. They are heteropolysaccharides composed of backbones of β-1,4-linked glucan with side chains of xylose, galactose, fucose, or arabinose residues and others (Figure 6; Fry, 2010). Oligoxyloglucans (XGOs) derived from the breakdown of xyloglucan in plant cell walls are emerging as biostimulants. Indeed, a study has shown that XGOs included in culture media stimulated growth of A. thaliana (González-Pérez et al., 2012). The XGOs implicated in this biostimulant activity are mainly XLLG and XXLG and in lower proportions XXXG and XXGG according to xyloglucan nomenclature (Fry et al., 1993). XGOs in the culture medium also increased salt stress tolerance of Arabidopsis by enhancing CAT gene expression, POX activity, and chlorophyll a/b ratios while reducing protein oxidation and total polyphenol content (González-Pérez et al., 2018). These XGOs had the same effect on N. tabacum seedlings under salt stress conditions by increasing the number of leaves, primary root length, lateral root formation, and proline and chlorophyll contents and reducing protein oxidation and lipid peroxidation (Páez-Watson et al., 2020). In addition, a patent claims that foliar application of XGOs improves cold stress resistance in V. vinifera and Actinidia deliciosa (A. Chev.) C.F. Liang & A.R. Ferguson (Salvador and Lasserre, 2010).
半纖維素（約佔細胞壁的 20-40%）和纖維素是結構相關的化合物（另見第 2.1.3 節），在細胞壁中密切相關。這兩種雜多糖都以 β-1,4-連接糖的主鏈為特徵，分為三類：（1） 葡聚糖，如木葡聚糖和 β-葡聚糖，（2） 木聚糖，如木聚糖和阿拉伯木聚糖，以及 （3） 甘露聚糖，如葡甘露聚糖和半乳糖葡甘露聚糖（Scheller 和 Ulvskov，2010 ）。 木葡聚糖是雙子葉植物初級細胞壁中最豐富的半纖維素。它們是雜多糖，由 β-1,4-連接的葡聚糖的主鏈與木糖、半乳糖、岩藻糖或阿拉伯糖殘基等的側鏈組成（圖 6;Fry，2010 年）。從植物細胞壁中木葡聚糖分解衍生的低聚木葡聚糖 （XGO） 正在成為生物刺激劑。事實上，一項研究表明，培養基中包含的 XGO 刺激了擬南芥的生長（González-Pérez et al.， 2012）。根據木葡聚糖命名法，與這種生物刺激劑活性有關的 XGO 主要是 XLLG 和 XXLG，以及較低比例的 XXXG 和 XXGG（Fry 等人， 1993 年）。培養基中的 XGO 還通過增強 CAT 基因表達、POX 活性和葉綠素 a/b 比率，同時減少蛋白質氧化和總多酚含量，增加了擬南芥的鹽脅迫耐受性（González-Pérez 等人， 2018 年）。這些 XGO 對 N 具有相同的影響 。 鹽脅迫條件下的油麻幼苗通過增加葉子數量、主根長度、側根形成、脯氨酸和葉綠素含量並減少蛋白質氧化和脂質過氧化（Páez-Watson et al.， 2020）。此外，一項專利聲稱，葉面施用 XGOs 可以提高 V. vinifera 和 Actinidia deliciosa （A. Chev.） C.F. Liang & A.R. Ferguson （Salvador and Lasserre， 2010） 的抗冷應激能力。

Xyloglucan oligosaccharides are also considered DAMPs. They elicited MAPK activation and immune gene expression like PR, phytoalexin deficient (PAD), and defensins in V. vinifera and A. thaliana (Claverie et al., 2018). Additionally, the authors demonstrated that xyloglucan conferred resistance against the pathogens Botrytis cinerea and Hyaloperonospora arabidopsidis.
木葡聚糖低聚糖也被認為是 DAMP。它們在 V. vinifera 和 A. thaliana 中引發了 MAPK 啟動和免疫基因表達，如 PR、植物抗毒素缺陷 （PAD） 和防禦素（Claverie 等人， 2018 年）。此外，作者證明木葡聚糖賦予對病原體灰黴菌和擬南芥透明腹孢菌的抗性。

Xylans are the predominant hemicelluloses in the cell walls of monocot plants. These polysaccharides have a xylose-containing backbone that is decorated with 4-O-methyl-D-glucopyranuronic acid, D-glucopyranuronic acid, L-arabinofuranosyl, and/or L-arabinopyranosyl units (Figure 6; Coté et al., 2008). Xylooligosaccharides (XOS), produced from xylan by enzymatic hydrolysis, applied in the culture substrat of Brassica rapa L. improved growth and tolerance to salinity stress by enhancing antioxidative systems, both enzymatic and non-enzymatic antioxidants, reduced lipid peroxidation, and increased the accumulation of osmolytes and the maintenance of the ionic balance (Chen et al., 2015). Applied to the soil of S. lycopersicum, XOS promoted the flowering of the plant, soil bacterial and actinomycete population, soil microbial biomass, nitrogen and phosphate content, and soil urease and phosphatase activities (Chen et al., 2012). Furthermore, XOS demonstrated plant defence properties, which were evidenced by the elicitation of stomatal closure via the salicylic acid (SA) signalling-mediated production of reactive oxygen species (ROS) and nitric oxide (NO, Zhang et al., 2021).
木聚糖是單子葉植物細胞壁中的主要半纖維素。這些多糖具有一個含木糖的主鏈，其修飾有 4-O-甲基-D-吡喃葡萄糖醛酸、D-吡喃葡萄糖醛酸、L-阿拉伯呋喃糖基和/或 L-阿拉伯吡喃糖基單元（圖 6;Coté et al.， 2008）。低聚木糖 （XOS），通過酶水解從木聚糖中得到，應用於 Brassica rapa L. 的培養基質。通過增強抗氧化系統（酶和非酶抗氧化劑）來改善生長和對鹽脅迫的耐受性，減少脂質過氧化，並增加滲透物的積累和離子平衡的維持（Chen 等人，2015 年）。施用於石松土壤，XOS 促進了植物的開花、土壤細菌和放線菌種群、土壤微生物量、氮和磷酸鹽含量以及土壤脲酶和磷酸酶活性（Chen et al.， 2012）。此外，XOS 表現出植物防禦特性，通過水楊酸 （SA） 信號介導的活性氧 （ROS） 和一氧化氮的產生誘導氣孔關閉證明瞭這一點（NO，Zhang 等人， 2021 年）。

Arabinoxylan-oligosaccharides and mixed-linked glucans also act as DAMPs in triggering immune responses including Ca²⁺ influx, ROS production, MAPK phosphorylation, expression of pattern-triggered immunity (PTI)-related genes, and enhanced pathogen resistance (Mélida et al., 2020; Rebaque et al., 2021).
阿拉伯木聚糖低聚糖和混合連接的葡聚糖在觸發免疫反應中也充當 DAMP，包括 Ca²⁺ 內流、ROS 產生、MAPK 磷酸化、模式觸發免疫 （PTI） 相關基因的表達和增強的病原體耐藥性（Mélida 等人， 2020 年;Rebaque et al.， 2021）。

Mannans, homopolymers of (1 → 4)-linked β-D-mannosyl residues, occur as storage polysaccharides and as structural polysaccharides in the primary and secondary cell walls of plants (Figure 6; Melton et al., 2009). Galactomannans are heteropolysaccharides with a main β-(1 → 4) mannose chain to which α-D-galactose units in O-6 positions are attached. They are closely related to plant gums and are found in soft-wood trees and seeds of several Fabaceae. Glucomannans are also heteropolysaccharides consisting of β-(1 → 4)-glucose and mannose units to form a linear polymer occasionally branched with galactose (galactoglucomannans).
甘露聚糖是 （1 → 4） -連接的 β-D-甘露糖基殘基的均聚物，在植物的初級和次級細胞壁中以儲存多糖和結構多糖的形式存在（圖 6;Melton et al.， 2009）。半乳甘露聚糖是具有主 β-（1 → 4） 甘露糖鏈的雜多糖，O-6 位的 α-D-半乳糖單元連接到該鏈上。它們與植物樹膠密切相關，存在於軟木樹和幾種豆科植物的種子中。葡甘露聚糖也是由 β-（1 → 4）-葡萄糖和甘露糖單元組成的雜多糖，形成偶爾與半乳糖支鏈的線性聚合物（半乳糖葡甘露聚糖）。

Galactomannans are used in several industries such as cosmetics, food, drilling, explosives, paper, petroleum, pharmaceuticals, and textiles (Lavudi and Suthari, 2020). Due to their water-soluble, stable, and highly viscous properties, they are also used in agriculture as water-retaining and/or pesticide- and fertilizer-delivery agents. Glucomannans also have food, biomedical, chemical, and environmental applications as absorbents for removal of pollutants (Yang et al., 2017).
半乳甘露聚糖用於多個行業，如化妝品、食品、鑽井、炸藥、造紙、石油、製藥和紡織（Lavudi 和 Suthari，2020 年）。由於其水溶性、穩定性和高粘度特性，它們在農業中也用作保水和/或殺蟲劑和肥料輸送劑。葡甘露聚糖還具有食品、生物醫學、化學和環境應用，可作為去除污染物的吸收劑（Yang et al.， 2017）。

We found no study on biostimulant activities of galactomannans or glucomannans. However, Zang et al., (2019) showed that oligomannans from Locust gum, applied to leaves of Nicotiana benthamiana Domin. and Oryza sativa, triggered various defense and resistance responses including elevation of intracellular Ca²⁺, ROS bursts, activation of MAPK and defense-related genes, hypersensitive cell death, and stomatal closure.
我們沒有發現關於半乳甘露聚糖或葡甘露聚糖的生物刺激劑活性的研究。然而，Zang 等人（2019 年）表明，來自刺槐膠的低聚甘露聚糖應用於 Nicotiana benthamiana Domin 的葉子。 和水稻 ，觸發各種防禦和抵抗反應，包括細胞內 Ca²⁺ 升高、ROS 爆發、MAPK 和防禦相關基因的啟動、過敏細胞死亡和氣孔關閉。

Pectins are the most complex polysaccharides in nature and the most abundant in the primary cell wall. Their structure mainly consists of galacturonic acid in the main chain and neutral sugars in the side chains. The main pectin domains are homogalacturonan (HG), rhamnogalacturonan-I (RG-I), rhamnogalacturonan II (RG-II), and xylogalacturonanes (Figure 7). Some other pectin motifs exist but are minor or plant-specific such as xylogalacturonan and apiogalacturonan. HG consists of 1,4-linked α-D-galacturonic acid and RG-I has a backbone of 1,4-α-D-GalpA-1,2-α-L-Rhap disaccharide repeating units with side chain decorations on the rhamosyl residues e.g. arabinan, galactan, or arabinogalactan. RG-II is a highly complex molecule with a backbone of 1,4-linked α-D-GalpA units to which four to six structurally conserved side chains are attached, consisting of twelve different monosaccharides like GalA and unusual sugars such as apiose, aceric acid, Kdo, and Dha (Lerouge et al., 2021; Yapo et al., 2007). Even though pectins are mainly found in land-plant cell walls, some forms are also found in seagrasses. Indeed, pectin isolated from the marine seagrass Zostera marina or the freshwater duckweed Lemna minor consists predominantly of apiogalacturonan. Apiogalacturonan is an HG backbone decorated with relatively frequent substitutions at O-3 of single residues or short oligosaccharides of D-apiose (Avci et al., 2017; Khasina et al., 2004). RG-I branching, as well as methyl- and acetylesterifications, has also been detected in the marine seagrass.
果膠是自然界中最複雜的多糖，在原代細胞壁中含量最高。它們的結構主要由主鏈中的半乳糖醛酸和側鏈中的中性糖組成。主要的果膠結構域是同型半乳糖醛酸酯 （HG）、鼠李糖乳糖醛酸酯-I （RG-I）、鼠李糖半乳糖醛酸酯 II （RG-II） 和木乳糖醛酸酯（圖 7）。存在一些其他果膠基序，但這些基序是次要的或植物特異性的，例如木醛酸糖漿和 apiogalacturonan。HG 由 1,4-連接的 α-D-半乳糖醛酸組成，RG-I 具有 1,4-α-D-GalpA-1,2-α-L-Rhap 二糖重複單元的主鏈，在鼠李糖基殘基上具有側鏈裝飾，例如阿拉伯聚糖、半乳聚糖或阿拉伯半乳聚糖。RG-II 是一種高度複雜的分子，具有 1,4 個連接的 α-D-GalpA 單元的主鏈，其上連接著 4 到 6 個結構保守的側鏈，由 12 種不同的單糖（如 GalA）和不常見的糖（如 apiose、aceric acid、Kdo 和 Dha）組成（Lerouge 等人， 2021 年;Yapo et al.， 2007）。儘管果膠主要存在於陸地植物細胞壁中，但也存在於海草中。事實上，從海洋海草 Zostera marina 或淡水浮萍 Lemna minor 中分離的果膠主要由 apiogalacturonan 組成。Apiogalacturonan 是一種 HG 骨架，在 O-3 處裝飾有相對頻繁的 D-apiose 的單個殘基或短寡糖（Avci 等人，2017 年;Khasina et al.， 2004）。在海洋海草中也檢測到 RG-I 分支以及甲基和乙醯酯化。

Several studies have highlighted pectin and their oligomers as biostimulants. Indeed, a study demonstrated that pectin-rich amendments can enhance Bacillus velezensis-mediated soybean growth promotion and nodulation by indigenous and inoculated Bradyrhizobium japonicum (Hassan et al., 2019). The application of aqueous solutions of citrus peel pectin nanospheres by dipping wheat seeds resulted in enhanced germination, the seeding stage, and net photosynthetic rate, as well as increased nutrient uptake (Li et al., 2021). Pectin-derived oligosaccharides with a degree of polymerization (DP) from three to six, applied on berries of V. vinifera, enhanced the synthesis and accumulation of anthocyanins and change of expression of key genes of the phenylpropanoid pathways (Villegas et al., 2016). Oligogalacturonides applied on tomato fruits promoted ripening by inducing ethylene (ET) synthesis through the regulation of ET synthesis genes (Ma et al., 2016). These pectin oligomers with a DP of seven to 15 applied on Medicago sativa L. seedlings also promoted root growth (Camejo et al., 2010). The oligomers with a DP around eight applied on Celosia argentea L. seedlings promoted shoot growth (Suzuki et al., 2002).
幾項研究強調果膠及其低聚物是生物刺激劑。事實上，一項研究表明，富含果膠的改良劑可以增強本地和接種的 Bradyrhizobium japonicum 介導的大豆生長促進和結瘤（Hassan et al.， 2019）。通過浸漬小麥種子施用柑橘皮果膠納米球的水溶液，可以提高發芽率、播種階段和凈光合速率，並增加養分吸收（Li et al.， 2021）。果膠衍生的低聚糖，聚合度 （DP） 從 3 到 6，應用於 V. vinifera 的漿果，增強了花色苷的合成和積累以及苯丙烷途徑關鍵基因表達的變化（Villegas 等人， 2016 年）。應用於番茄果實的低聚半乳糖醛通過調節 ET 合成基因誘導乙烯 （ET） 合成來促進成熟（馬等人， 2016 年）。這些 DP 為 7 到 15 的果膠低聚物施用於 Medicago sativa L. 幼苗也促進了根系生長（Camejo et al.， 2010）。將 DP 約為 8 的低聚物施用於 Celosia argentea L. 幼苗，促進芽的生長（Suzuki et al.， 2002）。

As a plant-innate elicitor, pectin-derived oligogalacturonides are the best characterized DAMPs. Their exogenous application could trigger PAMP-triggered immunity (PTI) responses including ET synthesis, inhibition of auxin action, accumulation of phytoalexins and callose, and production of ROS and NO (Howlader et al., 2020; Wang et al., 2022).
作為植物先天激發劑，果膠衍生的寡半乳糖醛酸酯是表徵最好的 DAMP。它們的外源性應用可以觸發 PAMP 觸發的免疫 （PTI） 反應，包括 ET 合成、生長素作用的抑制、植物抗毒素和胼胝體的積累以及 ROS 和 NO 的產生（Howlader 等人，2020 年;Wang et al.， 2022）。

2.2.1 Bacterial glycoproteins
2.2.1 細菌糖蛋白

Glycoproteins consist of carbohydrates covalently linked to proteins. Bacterial glycoproteins can be classified into five major types: (1) the surface-layer glycoproteins present in the outer most macromolecular monolayer of a bacterial cell envelope, (2) membrane–associated glycoproteins, distributed in the outer/inner membrane and in the periplasmic space of the bacteria, (3) cell-surface glycoproteins associated with pili or flagella, (4) secreted glycoproteins and exo-enzymes, and (5) cellular glycoproteins (Upreti et al., 2003). The most well-known bacterial glycoprotein is peptidoglycan (PGN), also called murein. It is present in almost all prokaryotic cell walls, except those of Archaea, and contributes to the shape of bacteria. It consists of a conserved glycan backbone of N-acetylglucosamine or N-acetylmuramic acid, cross-linked by short peptides, containing two to five amino acids like L-alanine, D-glutamate, a dibasic amino acid, and D-alanine (Figure 2; Irazoki et al., 2019).
糖蛋白由與蛋白質共價連接的碳水化合物組成。細菌糖蛋白可分為五大類：（1） 存在於細菌細胞包膜最外層大分子單層的表層糖蛋白，（2） 分佈在細菌的外/內膜和周質空間中的膜相關糖蛋白，（3） 與菌毛或鞭毛相關的細胞表面糖蛋白，（4） 分泌的糖蛋白和外切酶， （5） 細胞糖蛋白 （Upreti et al.， 2003）。最著名的細菌糖蛋白是肽聚糖 （PGN），也稱為胞壁蛋白。它幾乎存在於所有原核細胞壁中，除了古細菌的細胞壁，並有助於細菌的形狀。它由 N-乙醯葡糖胺或 N-乙醯胞壁酸的保守聚糖骨架組成，由短肽交聯，包含兩到五個氨基酸，如 L-丙氨酸、D-谷氨酸、一種二元氨基酸和 D-丙氨酸（圖 2;Irazoki 等人， 2019 年）。

No study has dealt with PGN or other bacterial glycoproteins as biostimulants. However, it is well known that PGN is considered a MAMP in many plant species such as A. thaliana, rice, and tobacco, because it induces immune responses including an increase in cytoplasmic Ca², accumulation of ROS and NO, camalexin production and post-translational induction of MAPK activities (Gust, 2015).
沒有研究將 PGN 或其他細菌糖蛋白作為生物刺激劑。然而，眾所周知，PGN 在許多植物物種（如擬南芥 、水稻和煙草）中被認為是 MAMP，因為它誘導免疫反應，包括細胞質 Ca² 的增加、ROS 和 NO 的積累、camalexin 的產生和 MAPK 活性的翻譯后誘導（Gust，2015 ）。

2.2.2 Fungal glycoproteins
2.2.2 真菌糖蛋白

The number of glycans present in glycoproteins differs greatly from one to more than 100 (Coté et al., 2008). N- and O-linked glycans are the most common forms of glycosylation in eukaryotic organisms. N-glycans are linked to proteins via the amide group of an asparagyl residue, and N-acetylglucosamine (GlcNAc) is found as the reducing terminal carbohydrate residue. O-glycans are linked to proteins via the hydroxy group of serine, threonine, and hydroproline. O-linked glycans feature a variety of terminal residues such as N-acetylgalactosamine, fucose, glucose, GlcNAc, xylose, galactose, arabinose, and O-linked mannose. In fungi, N-glycans contain mainly mannose residues, which are sometimes phosphorylated. Occasionally, residues such as galactose, pyruvate, galactofuranose, and β-1,2-linked mannose are also found. For fungal O-glycans, the situation is more variable, but O-linked mannosylation seems to be a typical feature (Coté et al., 2008).
糖蛋白中存在的聚糖數量差異很大，從 1 到 100 多種不等（Coté等人，2008 年）。N-和 O-連接聚糖是真核生物中最常見的糖基化形式。N-糖通過天冬醯胺殘基的醯胺基團與蛋白質連接，N-乙醯氨基葡萄糖 （GlcNAc） 被發現為還原性末端碳水化合物殘基。O-聚糖通過絲氨酸、蘇氨酸和氫脯氨酸的羥基與蛋白質連接。O-連接聚糖具有多種末端殘基，如 N-乙醯半乳糖胺、岩藻糖、葡萄糖、GlcNAc、木糖、半乳糖、阿拉伯糖和 O-連接甘露糖。在真菌中，N-糖主要包含甘露糖殘基，這些殘基有時會被磷酸化。偶爾也會發現半乳糖、丙酮酸、半乳呋喃糖和 β-1,2-連接甘露糖等殘基。對於真菌 O-聚糖，情況更加多變，但 O 連接甘露糖基化似乎是一個典型特徵（Coté等人， 2008）。

Only glomalin, produced by hyphae and spores of arbuscular mycorrhizal fungi (AMF), has a documented biostimulant activity. Indeed, glomalin-related protein applied by foliar spray to oranges (Citrus sinensis L.) improved soil fertility and fruit quality (Liu et al., 2022; Meng et al., 2021) and increased drought tolerance (Chi et al., 2018) and plant growth (Liu et al., 2021). Fungal glycoproteins from Fusarium oxysporum and Alternaria burnsii (respectively with molecular weight of 29 kDa and a 14 kDa) are also known as active elicitors, able to trigger immune responses in plants such as the accumulation of antioxidative enzymes and the synthesis of different phenolics and phytoalexins (Patel et al., 2020). Oligandrins, which are glycoproteins of fungus-like microorganisms (oomycetes) are also able to induce disease resistance in plants (Benhamou et al., 2001).
只有由叢枝菌根真菌 （AMF） 的菌絲和孢子產生的 glomalin 具有記錄的生物刺激活性。事實上，葉面噴施對柳丁 （Citrus sinensis L.） 的 glomalin 相關蛋白提高了土壤肥力和果實品質（Liu et al.， 2022;Meng et al.， 2021）和增加耐旱性 （Chi et al.， 2018） 和植物生長 （Liu et al.， 2021）。來自尖孢鐮刀菌和鏈格孢菌的真菌糖蛋白（分子量分別為 29 kDa 和 14 kDa）也稱為活性激發劑，能夠觸發植物中的免疫反應，例如抗氧化酶的積累以及不同酚類和植物抗毒素的合成（Patel 等人， 2020).寡甘苷是真菌樣微生物（卵菌）的糖蛋白，也能夠誘導植物的抗病性（Benhamou et al.， 2001）。

2.2.3 Seaweed glycoproteins
2.2.3 海藻糖蛋白

Only Chlorophyta exhibited hydroxyproline-rich glycoproteins (HRGPs) with characteristics like those from land plants. Arabinogalactan proteins (AGPs), extensins (EXTs), and extensin-like glycomolecules (pherophorins) have been detected and isolated from the protein-rich walls of green algae (Estevez et al., 2008). AGP-like structures were reported to also occur in brown algae (Hervé et al., 2016). No study implicating algal glycoproteins with biostimulant activities was found, and only one recent study dealt with plant elicitor properties of this glycomolecule. Indeed, an AGP-like enriched fraction from Ulva lactuca induced resistance to a fungal pathogen and triggered defense mechanisms like H₂O₂, SA, and ET signaling in Brassica napus L. (Přerovská et al., 2022).
只有綠藻門表現出富含羥脯氨酸的糖蛋白 （HRGPs），其特性與陸地植物相似。已經從富含蛋白質的綠藻壁中檢測到並分離出阿拉伯半乳聚糖蛋白 （AGP）、外延蛋白 （EXT） 和外延蛋白樣糖分子 （pherophorins） （Estevez 等人，2008 年）。據報導，AGP 樣結構也存在於褐藻中（Hervé等人， 2016 年）。沒有發現涉及藻類糖蛋白與生物刺激劑活性的研究，只有最近的一項研究涉及該糖分子的植物誘導特性。事實上，石莼中 AGP 樣富集部分誘導了對真菌病原體的耐藥性，並觸發了甘藍型油菜 L. 的 H₂O₂、SA 和 ET 信號傳導等防禦機制（Přerovská等人， 2022 年）。

2.2.4 Land-plant glycoproteins
2.2.4 陸地植物糖蛋白

N-glycoproteins and O-glycoproteins are two types of glycomolecules assembled and modified in the endoplasmic reticulum and Golgi apparatus before their transport within or outside the cell (Nguema-Ona et al., 2014). N-glycoproteins contain plant specific glycoepitopes such as a core β-(1,2)-xylose, core α-(1,3)-fucose residues, and possibly a Lewis antenna.
N-糖蛋白和 O-糖蛋白是兩種類型的糖分子，在內質網和高爾基體轉運到細胞內或細胞外之前，在內質網和高爾基體中組裝和修飾（Nguema-Ona 等人， 2014 年）。N-糖蛋白包含植物特異性糖表位，例如核心 β-（1,2）-木糖、核心 α-（1,3）-岩藻糖殘基，可能還有路易士天線。

O-glycoproteins are considered HRGPs and HRGPs are commonly divided into three major multigene families: AGPs, EXTs, and pro-rich proteins (PRPs). The common feature that defines this diverse family is the hydroxylation of Proline to Hydroxyproline (Hyp) and the subsequent attachment of O-linked glycans on Hyp residues (Figure 9; Johnson et al., 2017). The HRGPs range from highly glycosylated molecules, such as AGPs, to the moderately glycosylated EXTs and minimally glycosylated PRPs (Nguema-Ona et al., 2014).
O 糖蛋白被認為是 HRGP，HRGP 通常分為三大多基因家族：AGP、EXT 和富含原體的蛋白質 （PRP）。定義這個不同家族的共同特徵是脯氨酸羥基化為羥脯氨酸 （Hyp），以及隨後 O-連接聚糖附著在 Hyp 殘基上（圖 9;Johnson et al.， 2017）。HRGP 的範圍從高度糖基化的分子，如 AGP，到中度糖基化的 EXT 和最低糖基化的 PRP（Nguema-Ona 等人， 2014 年）。

In terms of biostimulation, AGP-rich extracts applied in the culture medium improved the differentiation of microspores derived from embryos of T. aestivum (Letarte et al., 2005). They enhanced the organogenesis of guard protoplast-derived callus and increased the number of shoots formed in Beta vulgaris L. (Wiśniewska and Majewska-Sawka, 2007). They also reduced cell mortality and increased the frequency of mitotic divisions of microspores and the number of multicellular structures of H. vulgare (Makowska et al., 2017). When gum arabic, a very well-known AGP-like molecule, was added to cell suspension cultures of V. vinifera it promoted cell growth (Cai et al., 2011). Derivatives of gum arabic from Acacia senegal (L.) Britton. incorporated in culture substrates significantly improved the growth of Catharanthus roseus (L.) G. Don in the number of leaves, height, and dry matter production (Ali et al., 2016).
在生物刺激方面，在培養基中施用富含 AGP 的提取物改善了源自 T. aestivum 胚胎的小孢子的分化（Letarte et al.， 2005）。它們增強了保護原生質體衍生的愈傷組織的器官發生，並增加了在 Beta vulgaris L. 中形成的芽的數量（Wiśniewska 和 Majewska-Sawka，2007 ）。 它們還降低了細胞死亡率，增加了小孢子有絲分裂的頻率和尋常紅孢子多細胞結構的數量（Makowska 等人， 2017 年）。當阿拉伯膠（一種非常著名的 AGP 樣分子）被添加到 V. vinifera 的細胞懸浮培養物中時，它會促進細胞生長（Cai et al.， 2011）。阿拉伯樹膠的衍生物，來自 Acacia senegal（L.） Britton。摻入培養基質中顯著改善了 Catharanthus roseus （L.） G. Don 在葉數、高度和乾物質產量方面的生長（Ali et al.， 2016）。

There is now scientific evidence that AGPs are involved in plant growth, development, and reproduction and in response to biotic and abiotic stress (Mareri et al., 2018), very few studies have shown their ability to function as elicitor or biocontrol compounds. Cai et al., (2011) showed that gum arabic included in cell suspension cultures of V. vinifera promoted the accumulation of phenolics. Cannesan et al., (2012) showed that AGPs extracted from pea root caps were able to prevent in vitro zoospore germination of the oomycete Aphanomyces euteiches.
現在有科學證據表明 AGP 參與植物的生長、發育和繁殖，並且響應生物和非生物脅迫（Mareri 等人，2018 年），很少有研究表明它們能夠作為誘發劑或生物控制化合物發揮作用。Cai et al.， （2011） 表明，包含在 V. vinifera 細胞懸浮培養物中的阿拉伯膠促進了酚類物質的積累。Cannesan 等人（2012 年）表明，從豌豆根帽中提取的 AGP 能夠防止卵菌 Aphanomyces euteiches 的體外遊動孢子萌發。

2.3.1 Bacterial glycolipids
2.3.1 細菌糖脂

Glycolipids are composed of carbohydrates with a hydrophilic moiety bound to lipids which are hydrophobic (Figure 10). Bacterial glycolipids are classified into 10 groups: lipopolysaccharides (LPS), rhamnolipids, rubiwettins, trehalolipids, other glycosylated mycolates, oligosaccharide lipids, glycosylated fatty alcohols, glycosylated macro-lactones/−lactams, glycocarotenoids/−terpenoids, and glycosylated hopanoids (Abdel-Mawgoud and Stephanopoulos, 2018).
糖脂由碳水化合物組成，親水部分與疏水性脂質結合（圖 10）。細菌糖脂分為 10 組：脂多糖 （LPS）、鼠李糖脂、紅濕素、海藻脂、其他糖基化菌物、低聚糖脂質、糖基化脂肪醇、糖基化大內酯/-內醯胺、類糖胡蘿蔔素/-萜類化合物和糖基化霍帕諾類（Abdel-Mawgoud 和 Stephanopoulos，2018 年）。

The most well-known bacterial glycolipids are LPS, rhamnolipids, and trehalolipids. All of them are well-recognized industrial substances whose applications are presented below.
最著名的細菌糖脂是 LPS、鼠李糖脂和海藻脂。它們都是公認的工業物質，其應用如下。

LPS are glycolipids, found in gram-negative bacteria, composed of three structural domains: an acylated β-1′-6-linked glucosamine disaccharide called the lipid A, the core oligosaccharide usually containing 3-deoxy-D-manno-2-octulosonic acid (Kdo) residues, heptoses, and various hexoses, which can be modified with phosphates and other substituents such as phosphoethanolamine, and an extended polysaccharide composed of a repeating oligosaccharide made of two to eight sugars called the O-antigen (Bertani and Ruiz, 2018).
LPS 是在革蘭氏陰性菌中發現的糖脂，由三個結構域組成：一種醯化的 β-1′-6-連接的葡萄糖胺二糖，稱為脂質 A，核心寡糖通常含有 3-去氧-D-甘露糖-2-八胞松酸 （Kdo） 殘基、庚糖和各種己糖，可以用磷酸鹽和其他取代基（如磷酸乙醇胺）修飾，以及由稱為 O 抗原的 2 到 8 個糖組成的重複寡糖組成的擴展多糖（Bertani 和 Ruiz，2018 年）。

LPS, otherwise also known as endotoxins, are widely used for medical, food, cosmetic, and environmental diagnostics (Stromberg et al., 2017). Agricultural applications have been studied less, but some studies have indicated biostimulant activities. Indeed, LPS isolated from Rhizobium leguminosarum bv. trifolii applied on seedlings of red clover (Trifolium pretense L.) showed an increase of plant yield (Głowacka et al., 2014). Those isolated from Azospirillum brasilense Sp245 applied by foliar spray on wheat (T. aestivum) increased leaf length, spike formation, and dry weight and accelerated plant growth (Chávez-Herrera et al., 2018). LPS also act as PAMPs in plants by triggering typical pattern-triggered immunity (PTI) responses inducing the oxidative burst, NO production, Ca²⁺ influx, accumulation of PR gene transcripts, and cell-wall alterations that include deposition of callose and phenolics (Chaliha et al., 2018; Silipo et al., 2010).
LPS，也稱為內毒素，廣泛用於醫療、食品、化妝品和環境診斷（Stromberg et al.， 2017）。對農業應用的研究較少，但一些研究表明生物刺激劑具有活性。事實上，從 Rhizobium leguminosarum bv 中分離出的 LPS。將 trifolii 應用於紅三葉草 （Trifolium pretense L.） 的幼苗顯示植物產量增加（Głowacka et al.， 2014）。通過葉面噴施小麥 （T. aestivum） 從 Azospirillum brasilense Sp245 中分離出來的那些增加了葉長、穗狀花序的形成和乾重，並加速了植物的生長（Chávez-Herrera et al.， 2018）。LPS 還通過觸發典型的模式觸發免疫 （PTI） 反應在植物中充當 PAMP，誘導氧化爆發、NO 產生、Ca²⁺ 內流、PR 基因轉錄物的積累以及包括胼胝質和酚類物質沉積在內的細胞壁改變（Chaliha 等人， 2018 年;Silipo et al.， 2010）。

Rhamnolipids contain a hydrophilic group, consisting of either one or two L-rhamnose residues, with a glycosidic linkage to the hydrophobic group made up of one or two β-hydroxy fatty acids (Figure 10). They are isolated from different strains of the Pseudomonas, Burkholderia, or Acinetobacter genera.
鼠李糖脂包含一個親水基團，由一個或兩個 L-鼠李糖殘基組成，與由一個或兩個 β-羥基脂肪酸組成的疏水基團具有糖苷鍵（圖 10）。它們是從假單胞菌屬、 伯克霍爾德氏菌屬或不動桿菌屬的不同菌株中分離出來的。

Very few of them were studied in biostimulant applications. However, one study dealt with rhamnolipid 90 isolated from Pseudomonas aeruginosa applied on the soil of spring barley (H. vulgare) that was demonstrated to be an effective biostimulant of soil enzyme activities like dehydrogenases, arylsulphatase, and β-glucosidase (Zaborowska et al., 2020). Another study showed that application of rhamnolipids and EPS on seeds of Z. mays, Lupinus luteus L., Pisum sativum L., Avena sativa L., and Sinapsis alba L. stimulated seed germination and plant growth (Krawczynska et al., 2012). In addition, these glycolipids have several industrial applications including as emulsifiers, spreaders, dispersing agents, and recently as potential agents of bioremediation of contaminated soils (Celligoi et al., 2020; Chong and Li, 2017). They are also used as pest control, biocontrol agents against several phytopathogens, and stimulants for plant immunity. As a plant-immunity elicitor, rhamnolipids induce accumulation of ROS, Ca²⁺ influx, phosphorylation cascades, callose deposition, hormone production, defense-gene activation, and a hypersensitive reaction-like response (Crouzet et al., 2020).
其中很少有在生物刺激劑應用中進行研究。然而，一項研究涉及從銅綠假單胞菌中分離的鼠李糖脂 90，應用於春大麥 （H. vulgare） 的土壤，它被證明是脫氫酶、芳基磺酸酶和 β-葡萄糖苷酶等土壤酶活性的有效生物刺激劑（Zaborowska 等人，2020 年）。另一項研究表明，將鼠李糖脂和 EPS 施用於 Z. mays、Lupinus luteus L.、Pisum sativum L.、Avena sativa L. 和 Sinapsis alba L. 的種子可刺激種子發芽和植物生長（Krawczynska et al.， 2012）。此外，這些糖脂具有多種工業應用，包括用作乳化劑、撒布劑、分散劑，最近還作為受污染土壤生物修復的潛在劑（Celligoi 等人， 2020 年;Chong 和 Li，2017 年）。它們還用作害蟲防治、針對多種植物病原體的生物防治劑和植物免疫興奮劑。作為植物免疫誘發劑，鼠李糖脂誘導 ROS 積累、Ca²⁺ 內流、磷酸化級聯反應、胼胝質沉積、激素產生、防禦基因啟動和超敏反應樣反應（Crouzet 等人， 2020 年）。

Trehalolipids contain a non-reducing disaccharide in which the two glucose units are linked in an α,α-1,1-glycosidic linkage. They are produced by Arthrobacter sp., Corynebacterium sp., Mycobacterium sp., Nocardia sp., and Rhodococcus erythropolis. Like the other biosurfactants, they are widely used in many industrial sectors such as petroleum, food, pharmaceuticals, and agriculture. However, despite their antimicrobial properties, to our knowledge, no study has dealt with their application as biostimulants or plant-defense elicitors (Paulino et al., 2016).
海藻脂含有一種非還原性二糖，其中兩個葡萄糖單元以 α，α-1,1-糖苷鍵連接。它們由節桿菌屬、 棒狀桿菌屬、 分枝桿菌屬、 諾卡氏菌屬和紅球菌產生 。與其他生物表面活性劑一樣，它們廣泛用於許多工業部門，如石油、食品、製藥和農業。然而，儘管它們具有抗菌特性，但據我們所知，還沒有研究涉及它們作為生物刺激劑或植物防禦誘導劑的應用（Paulino et al.， 2016）。

2.3.2 Fungal glycolipids
2.3.2 真菌糖脂

Glycolipids of fungi are classified into 10 groups: mannosylerythritol lipids (MELs), sophorolipids (Figure 10), cellobiose lipids, glucosyl-di-xylosyl lipids (glykenins), polyol fatty acid esters, glucosyl and mannosyl lipids, glycosylated polyketides, glucosyl-galactosyl lipids, glycosylated sterols, and glycosylated paraconic acids (Abdel-Mawgoud and Stephanopoulos, 2018). As bacterial glycolipids (see Section 2.3.1), several of them are well-known industrial compounds used as biosurfactants and bioemulsifiers and recently as potential agents of bioremediation of contaminated soils (Celligoi et al., 2020).
真菌的糖脂分為 10 組：甘露糖基赤蘚糖醇脂質 （MEL）、槐脂（圖 10）、纖維二糖脂質、葡萄糖基-二木糖基脂質（烯基 kenins）、多元醇脂肪酸酯、葡萄糖 基和甘露糖基脂質、糖基化聚酮、葡萄糖基-半乳糖基脂質、糖基化甾醇和糖基化對圓錐酸（Abdel-Mawgoud 和 Stephanopoulos，2018 年）。 作為細菌糖脂（參見第 2.3.1 節 ），其中一些是眾所周知的工業化合物，用作生物表面活性劑和生物乳化劑，最近用作受污染土壤生物修復的潛在劑（Celligoi 等人， 2020 年）。

To the best of our knowledge, only sophorolipids (Figure 10; mainly produced by yeasts) have been reported for their biostimulant activities. In agricultural applications, sophorolipids were first studied as antimicrobial agents against several plant pathogens (Celligoi et al., 2020; Chen et al., 2020). Other recent studies have shown that soil application of these glycolipids improves the growth of M. sativa and Bidens Pilosa, reduces the Cd stress, and improves soil microbial activities (Shah and Daverey, 2021).
據我們所知，只有槐脂（圖 10;主要由酵母產生）的生物刺激劑活性被報導。在農業應用中，槐脂首先被研究為針對幾種植物病原體的抗菌劑（Celligoi 等人， 2020 年;Chen 等人， 2020 年）。最近的其他研究表明，這些糖脂的土壤施用可以改善 M. sativa 和 Bidens Pilosa 的生長，減少 Cd 應力，並改善土壤微生物活性（Shah 和 Daverey，2021 ）。

MELs also have antimicrobial activity against phytopathogens and seem to have promising biostimulant activities by improving soil quality, contributing to plant nutrition, and stimulating plant growth (Matosinhos et al., 2022).
MEL 還對植物病原體具有抗菌活性，並且通過改善土壤品質、促進植物營養和刺激植物生長，似乎具有很有前途的生物刺激活性（Matosinhos et al.， 2022）。

2.3.3 Seaweed glycolipids
2.3.3 海藻糖脂

Three major types of glycolipids are found in seaweeds and marine grasses: monogalactosyldiacylglycerides (MGDGs), digalactosyldiacylglycerides (DGDGs), and sulfoquinovosyldiacylglycerides (SQDGs). MGDGs and DGDGs contain galactose linked to the sn-3 position of the glycerol backbone. SQDGs contain 6-deoxyglucose (quinovose) with a sulfonic group in the 6-position (Khotimchenko, 2002; Plouguerné et al., 2014).
在海藻和海草中發現了三種主要類型的糖脂：單半乳糖基二醯基甘油酯 （MGDGs）、二乳糖基二醯基甘油酯 （DGDGs） 和磺基喹諾糖基二醯基甘油酯 （SQDGs）。MGDG 和 DGDG 含有與甘油骨架的 sn-3 位置相連的半乳糖。SQDG 含有 6-去氧葡萄糖（喹諾糖），在 6-位有一個磺酸基團（Khotimchenko，2002 年; Plouguerné et al.， 2014）。

To date, no published study has dealt with algal glycolipids as biostimulants or any other agricultural use. On the other hand, these glycolipids have several medical and biological activities such as antibacterial, anti-tumor, antiviral, anti-inflammatory, and antioxidant properties (Plouguerné et al., 2014). Moreover, in algal metabolism, they play an important role for energy supply and cell protection against stresses such as osmotic and salt stresses (Terme et al., 2021).
迄今為止，還沒有已發表的研究將藻類糖脂作為生物刺激劑或任何其他農業用途。另一方面，這些糖脂具有多種醫學和生物活性，例如抗菌、抗腫瘤、抗病毒、抗炎和抗氧化特性（Plouguerné et al.， 2014）。此外，在藻類代謝中，它們在能量供應和細胞保護免受滲透壓和鹽脅迫等壓力方面發揮著重要作用（Terme 等人， 2021 年）。

2.3.4 Land plant glycolipids
2.3.4 陸地植物糖脂

Glycolipids play an important role in chloroplast development and morphology. Sterylglucosides (SGs), acylated sterylglucosides (ASGs), MGDGs, and DGDGs are the glycolipids contained in higher plants. Like seaweeds, MGDGs and DGDGs are major plant glycolipids and represent nearly 80% of the membrane lipids in chloroplasts. But small quantities of them are also found in non-photosynthetic plastids such as chromoplasts and amyloplasts (Kalisch et al., 2016; Rahim et al., 2018).
糖脂在葉綠體發育和形態中起重要作用。甾基葡糖苷 （SGs）、醯化甾基葡糖苷 （ASG）、MGDGs 和 DGDGs 是高等植物中所含的糖脂。與海藻一樣，MGDG 和 DGDG 是主要的植物糖脂，占葉綠體中膜脂的近 80%。但它們中的少量也存在於非光合質體中，例如著色質體和澱粉質體（Kalisch 等人，2016 年;Rahim et al.， 2018）。

No formal study has explored plant glycolipids as biostimulants or in any other agricultural use. Moreover, in the metabolism of higher plants, these glycolipids ensure protection against abiotic stresses such as drought and salinity (Ge et al., 2022; Mohamed et al., 2018). MGDGs and DGDGs are also known for their role in mediating the systemic acquired resistance (SAR) process of plant defense (Chaliha et al., 2018).
沒有正式的研究探索植物糖脂作為生物刺激劑或任何其他農業用途。此外，在高等植物的新陳代謝中，這些糖脂確保免受乾旱和鹽度等非生物脅迫（Ge et al.， 2022;Mohamed et al.， 2018）。MGDG 和 DGDG 也因其在介導植物防禦的系統獲得性抗性 （SAR） 過程中的作用而聞名（Chaliha 等人， 2018 年）。

All the glycomolecules like polysaccharides, glycoproteins, and glycolipids exhibiting biostimulant activities are summarized in Table 2.
表 2 總結了所有表現出生物刺激劑活性的糖分子，如多糖、糖蛋白和糖脂。

As discussed above, glycomolecules often present both biostimulant and plant-immunity activities. Therefore, it is tempting to draw a parallel between sweet immunity and biostimulation.
如上所述，糖分子通常同時具有生物刺激劑和植物免疫活性。因此，人們很容易將甜蜜免疫力和生物刺激相提並論。