Mechanisms of exogenous ABA-induced drought tolerance in Idesia polycarpa seedlings revealed by integrated physiological, transcriptomic, and metabolomic analyses

Idesia polycarpa is an important woody oil crop widely used for edible and industrial oils, landscaping, bioenergy, medicine, and cosmetics. However, its drought tolerance remains poorly understood at the molecular level. This study investigated the effects of exogenous abscisic acid (ABA) on drought responses in I. polycarpa seedlings. Drought stress reduced chlorophyll content and thinned leaf tissues, whereas ABA treatment maintained chlorophyll levels and increased palisade tissue thickness. Physiologically, ABA enhanced leaf relative water content, promoted osmolyte accumulation, reduced electrolyte leakage, and increased antioxidant enzyme activities. Integrated transcriptomic and metabolomic analyses revealed that ABA activated the plant hormone signaling pathway and the ascorbate–aldarate metabolism pathway, regulating the expression of key genes including PP2C51, TIFY10A, GID2, AUX22D, IAA27, and MIOX1, AKR4C9, thereby maintaining internal hormonal balance. Consequently, ABA, IAA, and GA levels increased, whereas JA and SA levels decreased. These findings indicate that exogenous ABA enhances drought tolerance in I. polycarpa seedlings through coordinated morphological, physiological, and molecular responses, providing a theoretical basis for seedling management and the development of drought-resistant cultivars.