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

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.