Exogenous ABA combined with cytokinin enhances drought resistance in Ziziphus jujuba Mill. var. spinosa by regulating xylem development and zeatin signaling pathway.

Drought is a decisive abiotic constraint limiting the growth and yield of jujube, its alleviation is orchestrated by a complex hormonal network that governs the tree's drought-resistance responses. Based on preliminary evidence that abscisic acid (ABA) and cytokinin play coordinated roles in drought adaptation, this study aimed to clarify their individual and combined effects on regulating drought resistance in sour jujube. Phenotypic responses, anatomical alterations, endogenous hormone profiles, and the expression levels of genes involved in the zeatin biosynthesis pathway after exogenous hormone spraying under drought stress were comprehensively analyzed. The results demonstrated that ABA and cytokinin significantly modulated drought adaptation of sour jujube across multiple aspects. Compared with the control group, ABA spraying xylem vessels number in leaf veins and roots, shortened stem internodes, and elevated the content of salicylic acid (SA), thereby enhancing drought resistance. In contrast, spraying cytokinin treatment increased drought sensitivity, expanded root xylem vessel diameter, and induced a slender stem and increased auxin content. Combined application of ABA and cytokinin was found to further increase vessel number and diameter in leaves and roots, improve branching density, and significantly increase SA, ABA, and jasmonic acid (JA) levels compared with single application of ABA and cytokinin. These factors may collectively enhance the drought resistance of sour jujube. Through weighted gene co-expression network analysis (WGCNA), candidate genes such as CGLD27, GNAT10, and LOC107415885 were obtained. Further analysis found that, both ABA and cytokinin inhibited zeatin biosynthesis, while accelerated trans-zeatin metabolism and delayed cis-zeatin turnover. Spraying of cytokinin enhanced isopentenyladenine degradation, which may reduce resistance, whereas downregulation of ZjZOG1, ZjZOG2, and ZjZOG3 may promote resilience. These findings provide a preliminary mechanistic framework for the role of ABA and cytokinin in drought adaptation of sour jujube.