Molecular mechanisms of ABA-mediated cold stress response in Dendrobium officinale

Dendrobium officinale, a valuable medicinal plant, is highly susceptible to cold stress, which particularly affects the accumulation of secondary metabolites. Abscisic acid (ABA) is a key hormone regulating plant responses to cold stress; however, the physiological and molecular mechanisms underlying exogenous ABA-mediated cold tolerance in D. officinale remain largely unknown. In this study, we investigated the effects of exogenous ABA application under cold stress on physiological and biochemical traits, gene expression profiles, and the accumulation of major medicinal components in D. officinale seedlings. At the physiological and biochemical level, exogenous ABA treatment significantly increased biomass accumulation and relative water content (RWC) in D. officinale under cold stress. It also elevated endogenous ABA levels, reduced stomatal conductance, and thereby enhanced water retention capacity. Compared with cold stress alone, plants subjected to combined ABA and cold treatments exhibited significantly lower malondialdehyde (MDA) content and electrolyte leakage, indicating reduced membrane lipid peroxidation. In addition, proline accumulation was promoted and chlorophyll degradation was alleviated. At the molecular level, transcriptomic analysis revealed the differential expression of multiple cold-responsive genes (e.g., DREB1, SKIP30, AP2-3, APRR9, Ubc12) as well as key genes involved in ABA biosynthesis and signaling pathways (e.g., NCED1, NCED2, PP2C50, SnRK1, PYR1-2). Furthermore, both cold stress and exogenous ABA treatment significantly modulated the expression of genes associated with polysaccharide and alkaloid biosynthesis, thereby promoting the accumulation of these medicinal compounds. Exogenous ABA application effectively alleviates cold stress-induced growth inhibition in D. officinale by enhancing endogenous ABA accumulation and inducing stomatal closure. Moreover, ABA treatment mitigates cold-induced membrane damage and regulates osmotic adjustment through the modulation of compatible solutes and secondary metabolites. These findings provide new insights into ABA-mediated signal transduction under cold stress and offer a theoretical basis for the development of cold-tolerant D. officinale cultivars.