REGULATION OF SEED GERMINATION BY PHYTOHORMONAL CROSS-TALK UNDER WATER DEFICIT CONDITIONS

Abstract

Water deficit conditions pose a significant threat to seed germination and early seedling establishment, particularly in drought-sensitive crops. This study investigated the phytohormonal cross-talk governing seed germination under drought stress using two sensitive (Zea_DS1, Glycine_DS2) and two tolerant (Zea_DT1, Glycine_DT2) genotypes. Seeds were subjected to varying levels of water stress (0 MPa, –0.3 MPa, –0.6 MPa) using polyethylene glycol (PEG-6000), and germination parameters were assessed alongside hormonal profiling and gene expression analyses. Results revealed that drought-sensitive genotypes exhibited significantly reduced germination rates (as low as 37.84%) and prolonged mean germination times under severe drought, with a concurrent decrease in germination index. Hormonal quantification showed a marked increase in abscisic acid (ABA) and decline in gibberellic acid (GA₃) levels under drought, especially in sensitive lines, indicating a shift toward an inhibitory hormonal environment. Gene expression analysis further confirmed the upregulation of NCED3, ABI5, and DELLA in drought-stressed seeds, highlighting the dominance of ABA signaling pathways. In contrast, tolerant genotypes maintained relatively stable hormone levels and gene expression patterns, enabling better germination under water stress. Hormonal inhibitor experiments validated these findings, where ABA inhibition partially restored germination, while GA inhibition exacerbated suppression. PCA analysis identified ABA and ABA-related gene markers as major contributors to drought response variation. Collectively, the study demonstrates that seed germination under water deficit is regulated by a dynamic, genotype-specific hormonal network, where the antagonism between ABA and GA is modulated by additional hormonal players such as IAA and ethylene. These findings provide valuable insights into the molecular basis of seed drought tolerance and offer potential targets for crop improvement strategies aimed at enhancing resilience during early growth stages.