Abscisic acid stimulates drought hardiness in cotton plants

Drought is a major environmental stress that can significantly impact the growth and productivity of agricultural crops, including cotton (Gossypium spp.). As a key cash crop, ensuring the resilience of cotton plants to drought conditions is crucial for maintaining sustainable agricultural production. One of the critical plant hormones involved in the drought response is abscisic acid (ABA). Abscisic acid, a vital plant hormone, plays a crucial role in the plant's adaptation to various abiotic stresses, including drought, by enhancing drought hardiness through regulating water loss, inducing stomatal closure, and controlling gene expression related to stress tolerance. Therefore, the present study was carried out to investigate the efficacy of exogenous abscisic acid (ABA) application on the growth and various physiological characteristics of drought-stressed and unstressed cotton plants. A foliar spray of abscisic acid (ABA) was applied as pretreatments to water-stressed cotton plants (cultivar Giza-90). Two concentrations of ABA were used: 40 μM and 80 μM. Water irrigation was applied as normal irrigation at 100% full field capacity (FC) and drought stress (50% FC). Growth attributes were measured, and the contents of leaf pigments (chlorophyll a, b, and carotenoids), amino acids, proline, sugars, flavonoids, and phenolic compounds were estimated. Additionally, antioxidant enzyme activities (catalase and peroxidase) and protein profiles were analyzed. The results showed that water shortage stress decreased cotton growth characteristics and leaf pigment contents, while enhancing the activities of antioxidant enzymes including catalase and peroxidase activities, free amino acids, proline, soluble sugars, total phenols, flavonoids, and lipid peroxidation. Drought stress induced the synthesis of the unique polypeptides 11, 20, and 100 KDa as drought-responsive proteins. Low concentration of ABA had minimal impact on plant growth; except for shoot-fresh weight in unstressed plants, but drought-stressed plants treated with 40 µM significantly increased plant growth and plant drought tolerance. Pretreatment with ABA at 80 µM significantly increased chlorophyll a and b, proline, phenols, peroxidase, catalase, and ascorbate peroxidase in stressed plants while decreasing lipid peroxidation, soluble sugars, and flavonoids stressed conditions. The interaction between drought stress and ABA induces a polymorphic polypeptide with 235 and 68 KDa. Pretreatment of cotton with ABA at optimal concentration can increase drought tolerance by enhancing physiological parameters, and photosynthetic pigments, regulating the protein metabolism and antioxidant capacity.