Impact of Abscisic Acid on Horticultural Crops Senescence: A Review

Abscisic acid (ABA) is a vital plant hormone, often referred to as the “stress hormone” due to its critical role in mediating plant responses to biotic and abiotic stressors. High concentrations of ABA are found in fleshy abscised leaves, a characteristic that inspired its name. The regulation of plant growth by ABA is context‐dependent, exerting either stimulatory or inhibitory effects depending on factors such as hormone concentration, tissue specificity, and environmental conditions. ABA plays a central role in a wide array of physiological and developmental processes, including stomatal closure; seed dormancy and germination; bud dormancy; floral transition; response to stresses such as drought, salinity, cold, ultraviolet (UV) radiation, and osmotic imbalance; leaf and floral senescence; fruit ripening; sugar metabolism; hypocotyl elongation; lateral root and epidermal development; cuticular wax and suberin accumulation; enhanced xylem differentiation; abscission of leaves, flowers, and fruits; fruit development and maturation; and seed degreening and maturation. Exogenous application of ABA has been shown to induce various physiological responses in horticultural crops, such as promoting primary root elongation, inducing stomatal closure and leaf abscission, enhancing embryo formation, increasing chilling and cold stress tolerance, stimulating of flowering, regulating leaf longevity and fruit quality, modulating fruit set (including both reduction and initiation), accelerating fruit ripening, accumulating soluble sugars, and reducing fruit cracking. Senescence, the final phase of plant development, is a genetically regulated process often triggered by internal and environmental cues, in which ABA plays a pivotal role. There are four significant types of senescence in plants: overall, top, organ, and monocarpic senescence. During senescence, nutrients are mobilized from source tissues and redirected to reproductive organs. In conclusion, whether produced endogenously or applied exogenously, ABA is a key regulator of the induction and progression of senescence in horticultural crop.