External application of vitexin enhances drought resistance by promoting the synthesis of flavonoids and other hormones and stabilizing the cell membrane in wheat (Triticum aestivum L.)

Drought damage has intensified through global warming, and drought stress is detrimental to wheat (Triticum aestivum
L.) yields. Although certain compounds (such as flavonoids) are used as a convenient and effective method to improve
plant drought resistance, the mechanism by which flavonoids affect plant drought resistance at the molecular level remains
unclear. We found that vitexin, a flavonoid compound, significantly improved drought tolerance in the wheat variety Chang
6878 at the seedling stage. Physiological and transcriptomic analysis during the seedling stage of wheat showed that
external application of vitexin increased the transcript-level expression of six genes, including phenylalanine deaminase
(PAL), chalcone isomerase (CHI), chalcone synthase (CHS), flavonol synthase II (FNSII), anthocyanin reductase (ANR),
and flavonoid 3′-hydroxylase (CYP75B1), which are involved in flavonoid synthesis and phenylpropanoid pathways under
drought conditions. The increased expression of these enzymes increased flavonoid accumulation, a phenomenon that
increases the antioxidant capacity and drought resistance of wheat. The content of plant hormones (salicylic acid, brassinolide, and ethylene) and linolenic acid increased significantly, whereas that of malondialdehyde decreased. This suggests
that externally applied vitexin can improve drought tolerance in wheat through phytohormonal pathways and maintenance
of cell membrane stability. Our results highlight the regulatory pathways of vitexin in wheat and suggest the future use
of vitexin as a bio-stimulant to enhance drought tolerance in wheat.