Integrated lipidomics and physiological analyses reveal the critical role of leaf sheath wax remodeling in wheat (Triticum aestivum L.) drought resistance

The increasing frequency of droughts driven by global warming poses a significant threat to wheat (Triticum aestivum L.) growth and yield. This study investigated stably inherited cuticular-wax mutants of wheat leaf sheaths, generated by ethyl-methanesulfonate (EMS) mutagenesis and isolated through phenotype-based screening. We systematically analyzed physiological responses, leaf sheath wax architecture, and lipid metabolism in a multi-wax mutant (mw; characterized by abundant leaf sheath wax crystals), a low-wax mutant (lw), and the wild type (WT) under both well-watered and drought conditions. Scanning electron microscopy (SEM) revealed a distinctive honeycomb-like network on the mw sheath epidermis, whereas the lw primarily displayed scattered block-like crystals. Under drought stress, lw leaves lost water significantly faster than mw (P < 0.01). Additionally, the mw leaf sheath exhibited significantly higher peroxidase (POD) and superoxide dismutase (SOD) activities, lower malondialdehyde (MDA) levels, and greater proline accumulation than lw (all P < 0.05). Untargeted lipidomics using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS) identified ten major lipid components, with fatty acids representing the largest proportion (25.7%). Aliphatic aldehydes and hydrocarbons were markedly enriched in mw and were positively correlated with drought tolerance indices. Overall, our results suggest that leaf-sheath wax enhances wheat adaptation to drought through the formation of a physical barrier together with modulation of lipid pathways, thereby promoting water retention and antioxidant defense. These findings provide novel metabolic insights into the drought-response mechanisms of leaf-sheath wax and lay a theoretical foundation for breeding drought-resilient wheat cultivars.