Seed germination is a critical phase during which plants are particularly sensitive to environmental stresses, especially heat stress, due to the high metabolic and physiological activities required for initial growth. Melatonin (MT), a key antioxidant, is crucial for assisting plants in managing abiotic stresses. While the impact of melatonin on heat stress has been explored in other developmental stages or species, this is the first study to specifically focus on its role during maize seed germination under heat stress. The treatment with 50 μM melatonin significantly enhanced seed germination under heat stress by improving antioxidant capacity, osmotic regulation, and hydrolytic enzyme activity, likely through the modulation of key signaling pathways, thus reducing oxidative damage and starch content. Furthermore, melatonin application promoted the accumulation of endogenous gibberellins (GAs) and significantly inhibited abscisic acid (ABA) content, thereby maintaining a dynamic equilibrium between these phytohormones. Principal component analysis and correlation analysis provided deeper insights into the overall effects of these physiological and biochemical parameters. Integrated transcriptomic and metabolomic analysis revealed that melatonin exerted its regulatory effects by modulating key genes and pathways associated with antioxidant defense, stress responses, and plant hormone signal transduction. Furthermore, melatonin significantly modulated the GA and ABA signaling pathways, starch and sucrose metabolism, and phenylpropanoid biosynthesis, thereby reducing oxidative damage induced by heat stress and strengthening the defense mechanisms of maize seeds. The alignment between the qRT-PCR findings and transcriptomic data further validated the robustness of these underlying mechanisms. In conclusion, this study provides novel insights into the role of melatonin in enhancing maize seed germination under heat stress and offers a promising strategy for improving crop heat tolerance through melatonin application in agricultural practices.

Isopentyltransferase (IPT) is a key rate-limiting enzyme in cytokinin synthesis, playing a crucial role in plant growth, development, and response to adverse conditions. Although the IPT gene family has been studied in various plants, comprehensive identification and functional characterization of IPT genes in maize (Zea mays) remain underexplored. In this study, ten IPT gene family members (ZmIPT1–ZmIPT10) were identified in the maize genome, and their gene structure, physicochemical properties, evolutionary relationships, expression patterns, and stress response characteristics were systematically analyzed. The ZmIPT genes were found to be unevenly distributed across six chromosomes, with most proteins predicted to be basic and localized primarily in chloroplasts. Phylogenetic analysis grouped the ZmIPT family into four subfamilies, showing close evolutionary relationships with rice IPT genes. Conserved motif and gene structure analyses indicated that the family members were structurally conserved, with five collinear gene pairs being identified. Ka/Ks analysis revealed that these gene pairs underwent strong purifying selection during evolution.Cis-element analysis of promoter regions suggested that ZmIPT genes are widely involved in hormone signaling and abiotic stress responses. Tissue-specific expression profiling showed that ZmIPT5, ZmIPT7, and ZmIPT8 were highly expressed in roots, with ZmIPT5 exhibiting consistently high expression under multiple abiotic stresses. qRT-PCR validation confirmed that ZmIPT5 expression peaked at 24 h after stress treatment, indicating its key role in long-term stress adaptation. Protein interaction analysis further revealed potential interactions between ZmIPT5 and cytokinin oxidases (CKX1, CKX5), as well as FPP/GGPP synthase family proteins, suggesting a regulatory role in cytokinin homeostasis and stress adaptation. Overall, this study provides comprehensive insights into the structure and function of the ZmIPT gene family and identifies ZmIPT5 as a promising candidate for improving stress tolerance in maize through molecular breeding.