Synergistic Regulation of Heat Tolerance in Waxy Maize ( <i>Zea mays</i> L. <i>var. ceratina Kulesh</i> ) by Exogenous Salicylic Acid and Nitric Oxide During the Jointing Stage

ABSTRACT Climate‐driven heat stress increasingly threatens waxy maize production, particularly during the jointing stage. Although exogenous salicylic acid (SA) and nitric oxide (NO) are known to improve heat tolerance in plants, their combined (SA‐NO) mechanisms in waxy maize remain unclear. This study investigated the effects of exogenous SA, NO and SA‐NO co‐application on alleviating heat stress in waxy maize during the jointing stage. Results revealed that high temperature (HT) severely impaired plant growth, elevating leaf oxidative damage, disrupting photosynthetic systems and reducing shoot dry weight by 42.7%, compared with the control. Exogenous application of SA, NO and SA‐NO mitigated these adverse effects, with the SA‐NO combination being most effective. Compared with HT, the SA‐NO reduced malondialdehyde and reactive oxygen species levels and increased shoot dry weight by 33.3%. Transcriptomic analysis revealed that SA‐NO upregulated photosynthesis‐related genes, stabilised starch and sucrose metabolism and glycolysis/gluconeogenesis pathways and enhanced activities of antioxidant enzymes. These changes helped reverse the HT‐induced declines in photosynthetic parameters. Additionally, SA‐NO restored hormonal balance by modulating ABA, IAA and CTK pathways, upregulating PYR/PYL and CRE1 while downregulating PP2C and SnRK2 . These results demonstrate that SA‐NO synergistically improves thermotolerance through enhanced antioxidant capacity, restored photosynthetic and hormonal regulation. This strategy offers a promising approach to protect heat‐stressed crops in a climate of change.