Polysaccharides Derived From the Brown Algae Lessonia nigrescens Enhance Salt Stress Tolerance to Wheat Seedlings by Enhancing the Antioxidant System and Modulating Intracellular Ion Concentration

Bio-stimulating effect of endophytic Aspergillus flavus AUMC 16068 and its respective ex-polysaccharides in lead stress tolerance of Triticum aestivum plant

Heavy metal accumulation is one of the major agronomic challenges that has seriously threatened food safety. As a result, metal-induced phytotoxicity concerns require quick and urgent action to retain and maintain the physiological activities of microorganisms, the nitrogen pool of soils, and the continuous yields of wheat in a constantly worsening environment. The current study was conducted to evaluate the plant growth-promoting endophytic Aspergillus flavus AUMC 16,068 and its EPS for improvement of plant growth, phytoremediation capacity, and physiological consequences on wheat plants (Triticum aestivum) under lead stress. After 60 days of planting, the heading stage of wheat plants, data on growth metrics, physiological properties, minerals content, and lead content in wheat root, shoot, and grains were recorded. Results evoked that lead pollution reduced wheat plants' physiological traits as well as growth at all lead stress concentrations; however, inoculation with lead tolerant endophytic A. flavus AUMC 16,068 and its respective EPS alleviated the detrimental impact of lead on the plants and promoted the growth and physiological characteristics of wheat in lead-contaminated conditions and also lowering oxidative stress through decreasing (CAT, POD, and MDA), in contrast to plants growing in the un-inoculated lead polluted dealings. In conclusion, endophytic A. flavus AUMC 16,068 spores and its EPS are regarded as eco-friendly, safe, and powerful inducers of wheat plants versus contamination with heavy metals, with a view of protecting plant, soil, and human health.

Azolla filiculoides extract improved salt tolerance in wheat (Triticum aestivum L.) is associated with prompting osmostasis, antioxidant potential and stress-interrelated genes

The growth and productivity of crop plants are negatively affected by salinity-induced ionic and oxidative stresses. This study aimed to provide insight into the interaction of NaCl-induced salinity with Azolla aqueous extract (AAE) regarding growth, antioxidant balance, and stress-responsive genes expression in wheat seedlings. In a pot experiment, wheat kernels were primed for 21 h with either deionized water or 0.1% AAE. Water-primed seedlings received either tap water, 250 mM NaCl, AAE spray, or AAE spray + NaCl. The AAE-primed seedlings received either tap water or 250 mM NaCl. Salinity lowered growth rate, chlorophyll level, and protein and amino acids pool. However, carotenoids, stress indicators (EL, MDA, and H2O2), osmomodulators (sugars, and proline), antioxidant enzymes (CAT, POD, APX, and PPO), and the expression of some stress-responsive genes (POD, PPO and PAL, PCS, and TLP) were significantly increased. However, administering AAE contributed to increased growth, balanced leaf pigments and assimilation efficacy, diminished stress indicators, rebalanced osmomodulators and antioxidant enzymes, and down-regulation of stress-induced genes in NaCl-stressed plants, with priming surpassing spray in most cases. In conclusion, AAE can be used as a green approach for sustaining regular growth and metabolism and remodelling the physio-chemical status of wheat seedlings thriving in salt-affected soils.

Exopolysaccharides from agriculturally important microorganisms: Conferring soil nutrient status and plant health

A wide variety of microorganisms secretes extracellular polymeric substances or commonly known as exopolysaccharides (EPS), which have been studied to influence plant growth via various mechanisms. EPS-producing microorganisms have been found to have positive effects on plant health such as by facilitating nutrient entrapment in the soil, or by improving soil quality, especially by helping in mitigating various abiotic stress conditions. The various types of microbial polysaccharides allow for the compartmentalization of the microbial community enabling them to endure undressing stress conditions. With the growing population, there is a constant need for developing sustainable agriculture where we could use various PGPR to help the plant cope with various stress conditions and simultaneously enhance the crop yield. These polysaccharides have also found application in various sectors, especially in the biomedical fields, manifesting their potential to act as antitumor drugs, play a significant role in immune evasion, and reveal various therapeutic potentials. These constitute high levels of bioactive polysaccharides which possess a wide range of implementation starting from industrial applications to novel food applications. In this current review, we aim at presenting a comprehensive study of how these microbial extracellular polymeric substances influence agricultural productivity along with their other commercial applications.

Characterization of a Novel Polysaccharide Derived from Rhizospheric Paecilomyces vaniformisi and Its Mechanism for Enhancing Salinity Resistance in Rice Seedlings

Soil salinity is an important limiting factor in agricultural production. Rhizospheric fungi can potentially enhance crop salinity tolerance, but the precise role of signaling substances is still to be systematically elucidated. A rhizospheric fungus identified as Paecilomyces vaniformisi was found to enhance the salinity tolerance of rice seedlings. In this study, a novel polysaccharide (PPL2b) was isolated from P. vaniformisi and identified as consisting of Manp, Glcp, GalpA, and Galp. In a further study, PPL2b showed significant activity in alleviating salinity stress-induced growth inhibition in rice seedlings. The results indicated that under salinity stress, PPL2b enhances seed germination, plant growth (height and biomass), and biochemical parameters (soluble sugar and protein contents). Additionally, PPL2b regulates genes such as SOS1 and SKOR to decrease K+ efflux and increase Na+ efflux. PPL2b increased the expression and activity of genes related to antioxidant enzymes and nonenzyme substances in salinity-induced oxidative stress. Further study indicated that PPL2b plays a crucial role in regulating osmotic substances, such as proline and betaine, in maintaining the osmotic balance. It also modulates plant hormones to promote rice seedling growth and enhance their tolerance to soil salinity. The variables interacted and were divided into two groups (PC1 77.39% and PC2 18.77%) based on their relative values. Therefore, these findings indicate that PPL2b from P. vaniformisi can alleviate the inhibitory effects of salinity stress on root development, osmotic adjustment, ion balance, oxidative stress balance, and growth of rice seedlings. Furthermore, it suggests that polysaccharides produced by rhizospheric fungi could be utilized to enhance crop tolerance to salinity.

Algal Phycocolloids: Bioactivities and Pharmaceutical Applications

Seaweeds are abundant sources of diverse bioactive compounds with various properties and mechanisms of action. These compounds offer protective effects, high nutritional value, and numerous health benefits. Seaweeds are versatile natural sources of metabolites applicable in the production of healthy food, pharmaceuticals, cosmetics, and fertilizers. Their biological compounds make them promising sources for biotechnological applications. In nature, hydrocolloids are substances which form a gel in the presence of water. They are employed as gelling agents in food, coatings and dressings in pharmaceuticals, stabilizers in biotechnology, and ingredients in cosmetics. Seaweed hydrocolloids are identified in carrageenan, alginate, and agar. Carrageenan has gained significant attention in pharmaceutical formulations and exhibits diverse pharmaceutical properties. Incorporating carrageenan and natural polymers such as chitosan, starch, cellulose, chitin, and alginate. It holds promise for creating biodegradable materials with biomedical applications. Alginate, a natural polysaccharide, is highly valued for wound dressings due to its unique characteristics, including low toxicity, biodegradability, hydrogel formation, prevention of bacterial infections, and maintenance of a moist environment. Agar is widely used in the biomedical field. This review focuses on analysing the therapeutic applications of carrageenan, alginate, and agar based on research highlighting their potential in developing innovative drug delivery systems using seaweed phycocolloids.

Application of seaweed extracts to mitigate biotic and abiotic stresses in plants

Agriculture sector is facing a lot of constraints such as climate change, increasing population and the use of chemicals, and fertilizers which have significant influence on sustainability. The excessive usage of chemical fertilizers and pesticides has created a significant risk to humans, animals, plants, and the environment. To reduce the dependency on chemical fertilizers and pesticides a biological-based alternative is required. Seaweeds are essential marine resources that contain bioactive compounds and they have several uses in agriculture. The use of seaweed extracts in agriculture can mitigate stress, enhance nutrient efficiency, and boost plant growth. The use of seaweed extracts and their components activate several signaling pathways and defense-related genes/enzymes. In this review, an attempt has been made to explain how seaweed extracts and their bioactive components induce tolerance and promote growth under stress conditions.

Supplementation with Ascophyllum nodosum extracts mitigates arsenic toxicity by modulating reactive oxygen species metabolism and reducing oxidative stress in rice

Ascophyllum nodosum extract (ANE) is considered as an effective source of biostimulants that have the potential of ameliorating the negative impact of different abiotic stresses in plants. Considering the growth-promoting ability and other regulatory roles of ANE, the present investigation was executed to evaluate the role of ANE in conferring arsenic (As) tolerance in rice (Oryza sativa L. cv. BRRI dhan89). Rice seedlings (35-d-old) were exposed to two doses of sodium arsenate (As1 - 50 mg As kg-1 soil; As2 - 100 mg As kg-1 soil) at 25 days after transplanting through irrigation, whereas only water was applied to the control. Foliar application of 0.1% ANE was also supplemented under control as well as As-stressed conditions at 7 days intervals for 5 times. Arsenic-induced oxidative stress was evident through a sharp increase in lipid peroxidation, hydrogen peroxide, methylglyoxal, and electrolyte leakage in the As-treated plants. As a consequence, plant growth and biomass, leaf relative water content, as well as yield attributes were reduced noticeably. On the other hand, ANE supplemented plants accumulated enhanced levels of ascorbate and glutathione, their redox balance, and the activities of antioxidant and glyoxalase enzymes viz. ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, catalase, glutathione peroxidase, and activities of glyoxalase I and glyoxalase II, respectively. Furthermore, relative water content, plant growth, yield attributes and yield were increased in the As-treated rice plants with ANE supplementation. The results reflected that foliar spray with ANE alleviated As-induced oxidative stress in rice plants by modulating the antioxidative defense and glyoxalase system.

Improving Wheat Salt Tolerance for Saline Agriculture

Salinity is a major abiotic stress that threatens crop yield and food supply in saline soil areas. Crops have evolved various strategies to facilitate survival and production of harvestable yield under salinity stress. Wheat (Triticum aestivum L.) is the main crop in arid and semiarid land areas, which are often affected by soil salinity. In this review, we summarize the conventional approaches to enhance wheat salt tolerance, including cross-breeding, exogenous application of chemical compounds, beneficial soil microorganisms, and transgenic engineering. We also propose several new breeding techniques for increasing salt tolerance in wheat, such as identifying new quantitative trait loci or genes related to salt tolerance, gene stacking and multiple genome editing, and wheat wild relatives and orphan crops domestication. The challenges and possible countermeasures in enhancing wheat salinity tolerance are also discussed.

Trichoderma longibrachiatum TG1 increases endogenous salicylic acid content and antioxidants activity in wheat seedlings under salinity stress

Several studies have reported the deleterious effects of excessive salt stress on Triticum aestivum L. seedlings. Seed pretreatment with exogenous salicylic acid (SA) enhances plants to tolerate salt stress. Herein, the present study aims to investigate the potential of plant-growth-promoting fungus Trichoderma longibrachiatum (TG1) to increase the plant growth and enhance the salicylic acid (SA) contents and antioxidants activity in wheat seedlings under different concentrations of salt stress. Wheat seeds were pretreated in TG1 spore suspension before exposure to different salt stresses. Compared with 0, 50, 100, 150 salt stresses, the TG1 and NaCl increased the wheat seeds germination rate, germination potential and germination index significantly; the shoot height and root length were increased by an average of 39.45% and 29.73%, respectively. Compared to NaCl stress across the four concentrations (0, 50, 100, and 150 mM), the TG1 treated wheat seedlings increased SA concentration and phenylalanine ammonia-lyase activity (PAL) by an average of 55.87% and 24.10% respectively. In addition, the TG1+NaCl-treated seedlings increased superoxide dismutase (SOD), peroxidases (POD), and catalase (CAT) activities in the shoot by an average of 47.68%, 23.68%, and 38.65% respectively compared to NaCl-stressed seedlings. Significantly, the genes, SOD, CAT, and POD were relatively up-regulated in the salt-tolerant TG1-treated seedlings at all NaCl concentrations in comparison to the control. Wheat seedlings treated with TG1+NaCl increased the transcript levels of SOD, POD and CAT by 1.35, 1.85 and 1.04-fold at 50 mM NaCl concentration, respectively, compared with 0 mM NaCl concentration. Our results indicated that seeds pretreatment with TG1 could increase endogenous SA of plants and promote seedling growth under salt stress by improving enzymatic antioxidant activities and gene expression.

AMF colonization affects allelopathic effects of Zea mays L. root exudates and community structure of rhizosphere bacteria

Arbuscular mycorrhizal fungi (AMF) widely exist in the soil ecosystem. It has been confirmed that AMF can affect the root exudates of the host, but the chain reaction effect of changes in the root exudates has not been reported much. The change of soil microorganisms and soil enzyme vigor is a direct response to the change in the soil environment. Root exudates are an important carbon source for soil microorganisms. AMF colonization affects root exudates, which is bound to have a certain impact on soil microorganisms. This manuscript measured and analyzed the changes in root exudates and allelopathic effects of root exudates of maize after AMF colonization, as well as the enzymatic vigor and bacterial diversity of maize rhizosphere soil. The results showed that after AMF colonization, the contents of 35 compounds in maize root exudates were significantly different. The root exudates of maize can inhibit the seed germination and seedling growth of recipient plants, and AMF colonization can alleviate this situation. After AMF colonization, the comprehensive allelopathy indexes of maize root exudates on the growth of radish, cucumber, lettuce, pepper, and ryegrass seedlings decreased by 60.99%, 70.19%, 80.83%, 36.26% and 57.15% respectively. The root exudates of maize inhibited the growth of the mycelia of the pathogens of soil-borne diseases, and AMF colonization can strengthen this situation. After AMF colonization, the activities of dehydrogenase, sucrase, cellulase, polyphenol oxidase and neutral protein in maize rhizosphere soil increased significantly, while the bacterial diversity decreased but the bacterial abundance increased. This research can provide a theoretical basis for AMF to improve the stubble of maize and the intercropping mode between maize and other plants, and can also provide a reference for AMF to prevent soil-borne diseases in maize.

The Biostimulant Effect of Hydroalcoholic Extracts of Sargassum spp. in Tomato Seedlings under Salt Stress

Currently, the use of biostimulants in agriculture is a tool for mitigating certain environmental stresses. Brown algae extracts have become one of the most important categories of biostimulants in agriculture, and are derived from the different uses and positive results obtained under optimal and stressful conditions. This study aimed to examine the efficacy of a foliar application of a hydroalcoholic extract of Sargassum spp. and two controls (a commercial product based on Ascophyllum nodosum and distilled water) with regard to growth, the antioxidant system, and the expression of defense genes in tomato seedlings grown in nonsaline (0 mM NaCl) and saline (100 mM NaCl) conditions. In general, the results show that the Sargassum extract increased the growth of the seedlings at the end of the experiment (7.80%) compared to the control; however, under saline conditions, it did not modify the growth. The Sargassum extract increased the diameter of the stem at the end of the experiment in unstressed conditions by 14.85% compared to its control and in stressful conditions by 16.04% compared to its control. Regarding the accumulation of total fresh biomass under unstressed conditions, the Sargassum extract increased it by 19.25% compared to its control, and the accumulation of total dry biomass increased it by 18.11% compared to its control. Under saline conditions, the total of fresh and dry biomass did not change. Enzymatic and nonenzymatic antioxidants increased with NaCl stress and the application of algal products (Sargassum and A. nodosum), which was positively related to the expression of the defense genes evaluated. Our results indicate that the use of the hydroalcoholic extract of Sargassum spp. modulated different physiological, metabolic, and molecular processes in tomato seedlings, with possible synergistic effects that increased tolerance to salinity.

Application of Biostimulants in Tomato Plants (Solanum lycopersicum) to Enhance Plant Growth and Salt Stress Tolerance

Under the era of climate change, plants are forced to survive under increasingly adverse conditions. Application of biostimulants in plants is shown to mitigate the deleterious effects of abiotic stresses including salinity, enhancing plant tolerance and performance. The present study focuses on the effects of five biostimulants based on biocompost and biofertilizer compounds that have been applied to tomato plants grown in the presence (salt-stressed plants) or absence of salt stress (control plants). To study the beneficial effects of the biostimulants in tomato plants, a series of analyses were performed, including phenotypic and agronomic observations, physiological, biochemical and enzymatic activity measurements, as well as gene expression analysis (RT-qPCR) including genes involved in antioxidant defense (SlCu/ZnSOD, SlFeSOD, SlCAT1, SlcAPX), nitrogen (SlNR, SlNiR, SlGTS1) and proline metabolism (p5CS), potassium transporters (HKT1.1, HKT1.2), and stress-inducible TFs (SlWRKY8, SlWRKY31). Among all the biostimulant solutions applied to the plants, the composition of 70% biofertilizer and 30% biocompost (Bf70/Bc30) as well as 70% biocompost and 30% biofertilizer (Bc70/Bf30) formulations garnered interest, since the former showed growth promoting features while the latter displayed better defense responses at the time of harvesting compared with the other treatments and controls. Taken together, current findings provide new insight into the beneficial effects of biostimulants, encouraging future field studies to further evaluate the biostimulant effects in plants under a real environment which is compromised by a combination of abiotic and biotic stresses.

Genome Editing for Sustainable Crop Improvement and Mitigation of Biotic and Abiotic Stresses

Climate change poses a serious threat to global agricultural activity and food production. Plant genome editing technologies have been widely used to develop crop varieties with superior qualities or can tolerate adverse environmental conditions. Unlike conventional breeding techniques (e.g., selective breeding and mutation breeding), modern genome editing tools offer more targeted and specific alterations of the plant genome and could significantly speed up the progress of developing crops with desired traits, such as higher yield and/or stronger resilience to the changing environment. In this review, we discuss the current development and future applications of genome editing technologies in mitigating the impacts of biotic and abiotic stresses on agriculture. We focus specifically on the CRISPR/Cas system, which has been the center of attention in the last few years as a revolutionary genome-editing tool in various species. We also conducted a bibliographic analysis on CRISPR-related papers published from 2012 to 2021 (10 years) to identify trends and potential in the CRISPR/Cas-related plant research. In addition, this review article outlines the current shortcomings and challenges of employing genome editing technologies in agriculture with notes on future prospective. We believe combining conventional and more innovative technologies in agriculture would be the key to optimizing crop improvement beyond the limitations of traditional agricultural practices.

Effects of partial replacement of dietary flour meal with seaweed polysaccharides on the resistance to ammonia stress in the intestine of hybrid snakehead (Channa maculatus ♀ × Channa argus ♂)

The purpose of this study was to evaluate the effects of partial replacement of dietary flour meal with seaweed polysaccharides on survival rate, histology, intestinal oxidative stress levels, and expression of immune-related genes in hybrid snakeheads under acute ammonia stress. Four experimental diets were set: (C) basal diet with 0% of seaweed polysaccharides as the control group, (MR) basal diet with 10% of seaweed polysaccharides, (HR) basal diet with 15% of seaweed polysaccharides, (HF) basal diet with 10% of fish oil. After 60 days of feeding, fish fed with the diet of C group were sampled as the control group, and other fish were exposed to ammonia nitrogen for 48 h. Two concentrations of total ammonia nitrogen (TAN) were used in this study: 120 mg/L TAN (low concentration exposure group), and 1200 mg/L TAN (high concentration exposure group). After exposure to ammonia nitrogen for 48 h, fish were sampled. The results indicated that adding seaweed polysaccharides to the diet could improve the survival rate of hybrid snakeheads under high concentration of ammonia stress. Histopathological analysis demonstrated multiple abnormalities in gills and intestines after exposure to two concentrations of TAN. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and lactate dehydrogenase (LDH) were all increased in the MR group under two concentrations of TAN stress. The mRNA abundance of immune-related genes in fish intestinal tissues was significantly induced or inhibited. These results suggested that partial replacement of dietary flour meal with seaweed polysaccharides improved the ability of hybrid snakeheads to resist ammonia stress.

Bio-Stimulating Effect of Natural Polysaccharides from Lobularia maritima on Durum Wheat Seedlings: Improved Plant Growth, Salt Stress Tolerance by Modulating Biochemical Responses and Ion Homeostasis

Bioactivities of polysaccharides derived from halophyte plants have gained attention in recent years. The use of biostimulants in agriculture is an innovative method of dealing with environmental stressors affecting plant growth and development. Here, we investigated the use of natural polysaccharides derived from the halophyte plant Lobularia maritima (PSLm) as a biostimulant in durum wheat seedlings under salt stress. Treatment with polysaccharide extract (0.5, 1, and 2 mg/mL PSLm) stimulated in vitro wheat growth, including germination, shoot length, root length, and fresh weight. PSLm at 2 mg/mL provided tolerance to plants against NaCl stress with improved membrane stability and low electrolyte leakage, increased antioxidant activities (catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD)), enhanced leaf chlorophyll fluorescence, proline, and total sugar contents, decreased lipid peroxidation (MDA), and reactive oxygen species (H₂O₂) levels, and coordinated the efflux and compartmentation of intracellular ions. The expression profile analyses of ten stress-related genes (NHX1, HKT1.4, SOS1, SOD, CAT, GA20-ox1, GA3-ox1, NRT1.1, NRT2.1, and GS) using RT-qPCR revealed the induction of several key genes in durum wheat growing in media supplemented with PSLm extract, even in unstressed conditions that could be related to the observed tolerance. This study revealed that PSLm extract contributes to salt tolerance in durum wheat seedlings, thereby enhancing their reactive oxygen species scavenging ability, and provided evidence for exploring PSLm as a plant biostimulant for sustainable and organic agriculture.

Microalgae as biostimulants: a new approach in agriculture

This review aims to elucidate the state of the art of microalgae-based biostimulants as a tool in agriculture by summarizing the biologically active compounds factors that influence the use of microalgae biostimulants and their application methods in the field. Additionally, we examined the factors that support the use of microalgal biostimulants to face abiotic and biotic stress in crop plants. The use of microalgae in crop production and the benefits of seed preparation, foliar application, soil drenching, and hydroponic treatments were discussed. Furthermore, the use of these biostimulants in crop plants and their multiple benefits such as, better rooting, higher crop, fruit yields, drought and salinity tolerance, photosynthetic activity and pathogen resistance was thoroughly presented. The present situation of microalgal biostimulants and their difficulties in the market was analyzed, as well as the perspectives of their use. However, data shows that microalgal derived biostimulants can be used as an alternative for the protection of crops and plant growth regulators and play a significant key role in increasing the levels of production, yield and health of crops. Special interest needs to focus on investigating more microalgae species and their biological active compound factors, due to the largely untapped field. Perspectives regarding future research lines and development priorities were included.

A hybrid RSM-ANN-GA approach on optimisation of extraction conditions for bioactive component-rich laver (Porphyra dentata) extract

This research established the optimal conditions for infusion extraction (IE) and ultrasound-assisted extraction (UAE) of bioactive components from laver (Porphyra dentata) using response surface methodology (RSM) and artificial neural network coupled with genetic algorithm (RSM-ANN-GA). The variables, temperatures (60, 80, and 100 ℃) and times (10, 15, and 20 min) were designed to optimise total phenolic, total flavonoid, total amino acid, a* value, and R-phycoerythrin content of laver extract. The optimised condition for IE and UAE was achieved at 60 ℃ for 18.08 min and 80.66℃ for 14.76 min in RSM while showing 60 ℃ for 19 min and 80℃ for 15 min in the RSM-ANN-GA mode, respectively. Results revealed that RSM-ANN-GA provided better predictability and greater accuracy than the RSM model and laver extract from UAE gave the higher values of responses compared to those from IE. These findings highlight the high-efficient extraction method along with better statistical approach.

Potential applications of alginate oligosaccharides for biomedicine - A mini review

Extensive research on marine algae, especially on their health-promoting properties, has been conducted. Various ingredients with potential biomedical applications have been discovered and extracted from marine algae. Alginate oligosaccharides are low molecular weight alginate polysaccharides present in cell walls of brown algae. They exhibit various health benefits such as anti-inflammatory, anti-microbial, anti-oxidant, anti-tumor and immunomodulation. Their low-toxicity, non-immunogenicity, and biodegradability make them an excellent material in biomedicine. Alginate oligosaccharides can be chemically or biochemically modified to enhance their biological activity and potential in pharmaceutical applications. This paper provides a brief overview on alginate oligosaccharides characteristics, modification patterns and highlights their vital health promoting properties.

Purification and characterization of a fucoidan from the brown algae Macrocystis pyrifera and the activity of enhancing salt-stress tolerance of wheat seedlings

A fuciodan (Mw = 11.1 kDa) was obtained and purified from Macrocystis pyrifera (MPF). MPF was an acid heteropolysaccharide including fucose, mannose, xylose, galactose, rhamnose, glucuronic acid, and glucose in a molar ratio of 3.1:1.0:0.86:0.63:0.25:0.33:0.11. Sulfate content in MPF was 28.6%, and the molar ratio of fucose to sulfate (Fuc:SO42-) was 1.0:0.58. The structure of MPF was mainly consist of repeating →3)-β-L-Fucp (2SO3-)-(1→ and →4)-β-D-Xylp-(1→3)-β-L-Fucp(2SO3-)-(1→ and with α-L-Fucp-(1→ and →6)-α-D-Galp-(1→ in branches. Moreover, the effects of different MPF concentrations on plant salt tolerance were investigated. The results indicated that MPF could improve the salt tolerance of wheat seedlings. Among the five concentrations (0.05, 0.1, 0.5, 1, and 2 mg/ml), 0.5 and 1 mg/ml MPF were optimal for effective plant salt-resistance activity. These results suggested that MPF extracted from brown seaweed show potential as plant stimulators that may be used to improve salt resistance of plants.

Ulva lactuca Extract and Fractions as Seed Priming Agents Mitigate Salinity Stress in Tomato Seedlings

The present study investigates the effect of Ulva lactuca extract as seed-priming agent for tomato plants under optimal and salinity stress conditions. The aims of this experiment were to assess the effect of seed priming using Ulva lactuca extract in alleviating the salinity stress tomato plants were subjected to, and to find out the possible mechanism of actions behind such a positive effect via means of fractionation of the crude extract and characterization. Salinity application decreased the plant biomass and altered different physiological traits of tomato. However, the application of Ulva lactuca methanol extract (ME) and its fractions (residual fraction (RF), chloroform fraction (CF), butanol fraction (BF), and hexane fraction (HF)) at 1 mg·mL^-1 as seed priming substances attenuated the negative effects of salinity on tomato seedlings. Under salinity stress conditions, RF application increased the tomato fresh weight; while ME, RF, and HF treatments significantly decreased the hydrogen peroxide (H₂O₂) concentration and antioxidant activity in tomato plants. The biochemical analyses of Ulva lactuca extract and fractions showed that the RF recorded the highest concentration of glycine betaine, while the ME was the part with the highest concentrations of total phenols and soluble sugars. This suggests that these compounds might play a key role in the mechanism by which seaweed extracts mitigate salinity stress on plants.

Effects of low molecular weight polysaccharides from Ulva prolifera on the tolerance of Triticum aestivum to osmotic stress

Polysaccharides derived from seaweeds can be used as biostimulants to enhance plant resistance to different stressors. In this study, we investigated the effects of applying low molecular weight polysaccharides (LPU) derived from Ulva prolifera with 14.2 kDa on the responses of wheat (Triticum aestivum) to osmotic stress. The results showed that osmotic stress simulated using polyethylene glycol inhibited seedling growth, whereas we observed increases in the fresh weights and shoot lengths of seedlings treated with polysaccharide for 120 h. Furthermore, we observed enhanced activities of antioxidant enzymes, and significant reductions in malondialdehyde content of 23.13%, 19.82%, and 20.04% in response treatment for 120 h with 0.01%, 0.03%, and 0.05% LPU, respectively, relative to those in the group treated with polyethylene glycol alone. In all treatments, expression of the P5CS gene was upregulated to promote proline accumulation. Moreover, after 120 h, exogenously applied LPU induced the expression of stress-related genes, including SnRK2, Wabi5, Wrab18, and Wdhn13. Collectively, these findings indicate that LPU might have the effect of regulating the abscisic acid-dependent pathway in wheat, thereby increasing seedling antioxidant capacity and growth. Application of LPU may accordingly represent an effective approach for enhancing the resistance to osmotic stress in wheat.

Algae as New Kids in the Beneficial Plant Microbiome

Previously, algae were recognized as small prokaryotic and eukaryotic organisms found only in aquatic habitats. However, according to a recent paradigm shift, algae are considered ubiquitous organisms, occurring in plant tissues as well as in soil. Accumulating evidence suggests that algae represent a member of the plant microbiome. New results indicate that plants respond to algae and activate related downstream signaling pathways. Application of algae has beneficial effects on plant health, such as plant growth promotion and disease control. Although accumulating evidence suggests that secreted compounds and cell wall components of algae induce physiological and structural changes in plants that protect against biotic and abiotic stresses, knowledge of the underlying mechanisms and algal determinants is limited. In this review, we discuss recent studies on this topic, and highlight the bioprotectant and biostimulant roles of algae as a new member of the plant beneficial microbiome for crop improvement.

Evaluation of microalgae polysaccharides as biostimulants of tomato plant defense using metabolomics and biochemical approaches

Microalgal polysaccharides (PSs) may be an effective elicitor agent that can efficiently protect plants against biotic stresses. In this study, wee investigates, the effect of PS obtained from microalgae and cyanobacteria (D. salina MS002, P. tricorontum MS023, Porphyridium sp. MS081, Desmodesmus sp., D. salina MS067 and A. platensis MS001) on the biochemical and metabolomics markers linked to defense pathways in tomato plants. The phenylalanine ammonia lyase (PAL), chitinase, 1,3-beta-glucanase and peroxidase (POX) activities have been improved in tomato plants leaves treated by polysaccharides extracted from P. triocnutum (238.26%); Desmodesmus sp. (19.95%); P. triocnutum (137.50%) and Porphyridium sp. (47.28%) respectively. For proteins, polyphenols and H2O2, the maximum effect was induced by D. salina 067 (55.01%), Porphyridium sp. (3.97%) and A. platensis (35.08%) respectively. On the other hand, Gas Chromatography-mass spectrometry (GC-MS) metabolomics analysis showed that PSs induced the modification of metabolite profile involved in the wax construction of tomato leaves, such as fatty acids, alkanes, alkenes and phytosterol. PS treatments improved the accumulation of fatty acids C16:3, C18:2 and C18:3 released from the membrane lipids as precursors of oxylipin biosynthesis which are signaling molecules of plant defense. In addition, PS treatment induced the accumulation of C18:0 and Azelaic acid which is a regulator of salicylic acid-dependent systemic acquired resistance. However, molecular and metabolic studies can determine more precisely the mode of action of microalgal polysaccharides as biostimulants/elicitors plant defense.

Overexpression of DoUGP Enhanced Biomass and Stress Tolerance by Promoting Polysaccharide Accumulation in Dendrobium officinale

Uridine diphosphate glucose pyrophosphorylase (UDP-glucose pyrophosphorylase, UGPase), as one of the key enzymes in polysaccharide synthesis, plays important roles in the growth and development of plants. In this study, the DoUGP gene of Dendrobium officinale was overexpressed. The expression of DoUGP and genes playing roles in the same and other saccharide synthesis pathways was determined, and the total soluble polysaccharide was also tested in wild-type and transgenic seedlings. We also performed freezing and osmotic stress treatments to determine whether overexpression of DoUGP could influence stress resistance in transgenic seedlings. Results showed that mRNA expression levels of DoUGP and its metabolic upstream and downstream genes in the transgenic seedlings were increased compared to the expression of these genes in wild-type seedlings. Additionally, most CSLA genes involved in the biosynthesis of mannan polysaccharides were significantly upregulated. The total polysaccharide and mannose content of transgenic seedlings were increased compared to the content of wild type, and enhanced stress tolerance was found in the overexpressed seedlings compared to the wild type.

Enhancing Sustainability by Improving Plant Salt Tolerance through Macro- and Micro-Algal Biostimulants

Algal biomass, extracts, or derivatives have long been considered a valuable material to bring benefits to humans and cultivated plants. In the last decades, it became evident that algal formulations can induce multiple effects on crops (including an increase in biomass, yield, and quality), and that algal extracts contain a series of bioactive compounds and signaling molecules, in addition to mineral and organic nutrients. The need to reduce the non-renewable chemical input in agriculture has recently prompted an increase in the use of algal extracts as a plant biostimulant, also because of their ability to promote plant growth in suboptimal conditions such as saline environments is beneficial. In this article, we discuss some research areas that are critical for the implementation in agriculture of macro- and microalgae extracts as plant biostimulants. Specifically, we provide an overview of current knowledge and achievements about extraction methods, compositions, and action mechanisms of algal extracts, focusing on salt-stress tolerance. We also outline current limitations and possible research avenues. We conclude that the comparison and the integration of knowledge on the molecular and physiological response of plants to salt and to algal extracts should also guide the extraction procedures and application methods. The effects of algal biostimulants have been mainly investigated from an applied perspective, and the exploitation of different scientific disciplines is still much needed for the development of new sustainable strategies to increase crop tolerance to salt stress.

The aqueous extract and powder of the brown alga Dictyota dichotoma (Hudson) differentially alleviate the impact of abiotic stress on rice (Oryza sativa L.)

Algal supplements can improve crop productivity and afford protection against abiotic stress by virtue of their rich content of plant nutrients and bioactive compounds. The present work investigates the relative efficiency of the biomass and extract of the brown alga Dictyota dichotoma in protection of rice against salinity and water stress. Rice (Oryza sativa L.) cv. Sakha 101 was grown on a silty clay soil amended with the aqueous extract and powder of D. dichotoma under NaCl and PEG 6000 stress at water potential of - 0.492 MPa. Abiotic stress, particularly water stress, reduced rice growth and concentrations of K⁺ and protein but increased soluble sugars, starch, proline and Na⁺ concentrations of plant tissues, with counterbalancing effect of algal amendment. The benefit of algal amendment was greater for algal extract than algal powder and under water stress than salt stress. Algal amendment and abiotic stress promoted catalase and peroxidase activities in rice leaves with variable effect on polyphenol oxidase. The benefit of D. dichotoma to rice can be related to macro- and micro-nutrients, growth hormones, phenolics, flavonoids, sterols, vitamins and fucoidan. The production of toxic intermediates as a result of fermentation of the algal biomass in the paddy soil might reduce the benefit of algal amendment. Although rice is salt-sensitive, it is more resistant to salt stress than to drought stress. The ability of rice to retain Na⁺ in the root is pivotal for stress resistance, but the role of K⁺ partitioning is less evident.

Fucoidans: Downstream Processes and Recent Applications

Fucoidans are multifunctional marine macromolecules that are subjected to numerous and various downstream processes during their production. These processes were considered the most important abiotic factors affecting fucoidan chemical skeletons, quality, physicochemical properties, biological properties and industrial applications. Since a universal protocol for fucoidans production has not been established yet, all the currently used processes were presented and justified. The current article complements our previous articles in the fucoidans field, provides an updated overview regarding the different downstream processes, including pre-treatment, extraction, purification and enzymatic modification processes, and shows the recent non-traditional applications of fucoidans in relation to their characters.

Trends in Seaweed Extract Based Biostimulants: Manufacturing Process and Beneficial Effect on Soil-Plant Systems

The time when plant biostimulants were considered as "snake oil" is erstwhile and the skepticism regarding their agricultural benefits has significantly faded, as solid scientific evidences of their positive effects are continuously provided. Currently plant biostimulants are considered as a full-fledged class of agri-inputs and highly attractive business opportunity for major actors of the agroindustry. As the dominant category of the biostimulant segment, seaweed extracts were key in this growing renown. They are widely known as substances with the function of mitigating abiotic stress and enhancing plant productivity. Seaweed extracts are derived from the extraction of several macroalgae species, which depending on the extraction methodology lead to the production of complex mixtures of biologically active compounds. Consequently, plant responses are often inconsistent, and precisely deciphering the involved mechanism of action remains highly intricate. Recently, scientists all over the world have been interested to exploring hidden mechanism of action of these resources through the employment of multidisciplinary and high-throughput approaches, combining plant physiology, molecular biology, agronomy, and multi-omics techniques. The aim of this review is to provide fresh insights into the concept of seaweed extract (SE), through addressing the subject in newfangled standpoints based on current scientific knowledge, and taking into consideration both academic and industrial claims in concomitance with market's requirements. The crucial extraction process as well as the effect of such products on nutrient uptake and their role in abiotic and biotic stress tolerance are scrutinized with emphasizing the involved mechanisms at the metabolic and genetic level. Additionally, some often overlooked and indirect effects of seaweed extracts, such as their influence on plant microbiome are discussed. Finally, the plausible impact of the recently approved plant biostimulant regulation on seaweed extract industry is addressed.

N-3-oxo-hexanoyl-homoserine lactone, a bacterial quorum sensing signal, enhances salt tolerance in Arabidopsis and wheat

BACKGROUND

N-acyl-homoserine lactones (AHLs) are the quorum sensing (QS) signal molecules to coordinate the collective behavior in a population in Gram-negative bacteria. Recent evidences demonstrate their roles in plant growth and defense responses.

RESULTS

In present study, we show that the treatment of plant roots with N-3-oxo-hexanoyl-homoserine lactone (3OC6-HSL), one molecule of AHLs family, resulted in enhanced salt tolerance in Arabidopsis and wheat. We found that the growth inhibition phenotype including root length, shoot length and fresh weight were significantly improved by 3OC6-HSL under salt stress condition. The physiological and biochemical analysis revealed that the contents of chlorophyll and proline were increased and the contents of MDA and Na⁺ and Na⁺/K⁺ ratios were decreased after 3OC6-HSL treatment in Arabidopsis and wheat under salt stress condition. Molecular analysis showed that 3OC6-HSL significantly upregulated the expression of salt-responsive genes including ABA-dependent osmotic stress responsive genes COR15a, RD22, ADH and P5CS1, ABA-independent gene ERD1, and ion-homeostasis regulation genes SOS1, SOS2 and SOS3 in Arabidopsis under salt stress condition.

CONCLUSIONS

These results indicated that 3OC6-HSL enhanced plant salt tolerance and ABA-dependent and ABA-independent signal pathways and SOS signaling might be involved in the induction of salt resistance by 3OC6-HSL in plants. Our data provide a new insight into the plant-microbe inter-communication.

Seaweed and seaweed-derived metabolites as prebiotics

Seaweeds and their bioactive compounds, particularly polysaccharides and phenolics can be regarded as great dietary supplements with gut health benefits and prebiotics. These components are resistant to digestion by enzymes present in the human gastrointestinal tract, also selectively stimulate the growth of beneficial gut bacteria and the production of fermentation products such as short chain fatty acids. Commonly, the health benefits of seaweed components are assessed by including them in an in vitro anaerobic fermentation system containing human fecal inocula that mimics the environment of the human large bowel. Regarding to the complex interactions between dietary components, gastrointestinal physiological processes, and gut microbiota are difficult to model in vitro. Consequently it is important to follow up the promising in vitro results with in vivo animal or human testing. The aim of this chapter is to have a comprehensive review on the application of seaweeds and seaweed-derived metabolites as prebiotics, and understand the trends, gaps and future directions of both scientific and industrial developments. This work contributes to develop and expand new platform of seaweed utilization for higher-value products, particularly to functional food and nutraceutical industries in order to serve the social demand for health awareness and support economic development.

Microalgae polysaccharides: the new sustainable bioactive products for the development of plant bio-stimulants?

Plant biostimulants are defined as materials containing microorganisms or substances whose function when applied to plants or the rhizosphere is to stimulate natural mechanisms to enhance plant growth, nutrient use efficiency, tolerance to abiotic stressors and crop quality, independent of their nutrient content. In agriculture, seaweeds (Macroalgae) have been used in the production of plant biostimulants while microalgae still remain unexploited. Microalgae are single cell microscopic organisms (prokaryotic or eukaryotic) that grow in a range of aquatic habitats, including, wastewaters, pounds, lakes, rivers, oceans, and even humid soils. These photosynthetic microorganisms are widely described as renewable sources of biofuels, bioingredients and biologically active compounds, such as polyunsaturated fatty acids (PUFAs), carotenoids, phycobiliproteins, sterols, vitamins and polysaccharides, which attract considerable interest in both scientific and industrial communities. Microalgae polysaccharides have so far proved to have several important biological activities, making them biomaterials and bioactive products of increasing importance for a wide range of applications. The present review describes microalgae polysaccharides, their biological activities and their possible application in agriculture as a potential sustainable alternative for enhanced crop performance, nutrient uptake and resilience to environmental stress. This review does not only present a comprehensive and systematic study of Microalgae polysaccharides as plant biostimulants but considers the fundamental and innovative principles underlying this technology.