Metabolic Pathways Regulated by Chitosan Contributing to Drought Resistance in White Clover

Abstract

Increased endogenous chitosan (CTS) could be associated with improved drought resistance in white clover (Trifolium repens). Plants were pretreated with or without 1 mg/mL CTS and then were subjected to optimal or water-limited condition in controlled growth chambers for 6 days. Phenotypic and physiological results indicated that exogenous CTS significantly improved drought resistance of white clover. Metabolome results showed that exogenous CTS induced a significant increase in endogenous CTS content during dehydration accompanied by the maintenance of greater accumulation of sugars, sugar alcohols, amino acids, organic acids, and other metabolites (ascorbate, glutathione, flavonoids, putrescine, and spermidine). These compounds are associated with osmotic adjustment, antioxidant defense, stress signaling, and energy metabolism under stress condition. Similarly, transcriptome revealed that many genes in relation to amino acid and carbohydrate metabolism, energy production and conversion, and ascorbate-glutathione and flavonoid metabolism were significantly up-regulated by CTS in response to dehydration stress. CTS-induced drought resistance was associated with the accumulation of stress protective metabolites, the enhancement of ascorbate-glutathione and tricarboxylic acid cycle, and increases in the γ-aminobutyric acid shunt, polyamine synthesis, and flavonoids metabolism contributing to improved osmotic adjustment, antioxidant capacity, stress signaling, and energy production for stress defense, thereby maintaining metabolic homeostasis under dehydration stress.

Nitric oxide, γ‐aminobutyric acid, and mannose pretreatment influence metabolic profiles in white clover under water stress

“…Multiple previous studies have proven that the maintenance of metabolic balance, the activation of certain metabolic pathways, and the accumulation of specific metabolites are vital defensive and adaptive mechanisms when plants suffer from a harsh environment, such as drought or high temperature (Du et al ; Li et al , , ; Xu et al ). Based on metabonomics, SNP, GABA, and MAS regulated many metabolites and several major metabolic processes in common or differentially, including carbohydrates and amino acids metabolism, TCA cycle, GABA shunt, and other pathways, which could be contributed to SNP‐, GABA‐, and MAS‐induced stress adaptation in white clover (Figures –10).…”

“…Interestingly, the significant accumulation of galactose and xylose were only observed in MAS‐treated white clover as compared to untreated plants under water stress (Figure ). It has been found that the improved tolerance to water stress was correlated with chitosan‐induced accumulation of galactose and xylose in white clover (Li et al ). The severe drought together with high temperature led to greater increases in glucose and galactose content conferring better OA in poplar ( Populus ) leaves (Jia et al ).…”

“…Glycerol is also involved in lipid formation, glycolysis, and the synthesis of glycerol‐3‐phosphate that is a novel regulator of defense signaling in plants (Venugopal et al ). It has been reported that the accumulation of glycerol could be related to increased drought tolerance in creeping bentgrass and white clover (Li et al ; Xu et al ). Our current findings suggested that SNP and GABA resulted in an increase in myo‐inositol content and the accumulation of glycerol was commonly regulated by GABA and MAS contributing to enhanced drought tolerance via the improvement of stress defense signal transduction, membrane integrity, and water balance in white clover.…”

“…The metabolite extraction, separation, and quantification were conducted according to methods of Lytovchenko and Fernie (2002) and Qiu et al (2009) with some modifications, which were clearly decribed in our previous study (Li et al 2017c).…”

Recent Advances of Chitosan Applications in Plants

“…Interesting results were obtained using CHT to protect plants against abiotic stresses. CHT (1 mg/mL, origin and characteristics not further specified, viscosity 5−30 mPa s, added 2 days before exposition of plants to dehydration stress) improves drought resistance in white clover (Trifolium repens) by enhancing the accumulation of stress protective metabolites [9]. Foliar application of CHT (200-400 µL/L, origin and characteristics not further specified, sprayed three times, just prior to flowering stage, at 50% flowering and at full bloom) reduces the negative impact of drought condition on dry matter and oil yield of Thymus daenensis Celak [10].…”