Myo-inositol mitigates heat-induced leaf senescence by enhancing antioxidant defense, sugar metabolism, and heat shock pathway in creeping bentgrass

Myo-inositol (MI) plays an important regulatory role in plant stress adaptation, but limited investigation has been conducted to reveal potential mechanisms of MI-regulated leaf senescence under heat stress. This study investigated how foliar-applied MI (0.5 mM) influences heat tolerance in cool-season creeping bentgrass by examining its effects on photosynthetic stability, sugar metabolism, the accumulation of pyruvic acid (PA), antioxidant defense systems, and heat shock transcription pathways. Plants with or without the exogenous MI application were subjected to high-temperature stress (35/30°C, day/night) for 14 days. Leaf samples were collected from four biological replicates (n = 4) per treatment at multiple time points (0 h, 3 h, 7 d, and 14 d) during the heat stress period. The results showed that heat stress induced damage symptoms including reduced leaf relative water content, chlorophyll loss, and declines in photosynthesis and photochemical efficiency, which could be significantly mitigated by exogenous MI. The application of MI significantly increased water use efficiency, the accumulation of sucrose, fructose, glucose, and PA as well as the activities of invertase, sucrose synthase, and sucrose phosphate synthase in favor of carbon acquisition, osmotic adjustment, and energy supply during heat stress. Under high-temperature stress, foliar spraying of MI significantly reduced electrolyte leakage and contents of superoxide anion radicals, hydrogen peroxide, and malondialdehyde by improving activities of antioxidant enzyme activities (SOD, POD, CAT, APX, MR, GR, and DR), the accumulation of non-enzymatic antioxidants (ASA and GSSG), and the ASA/DHA ratio. In addition, heat stress significantly up-regulated expression levels of multiple genes encoding heat shock transcription factors (HSFA-2c, HSFA-2d, HSFA-6a, and HSFC-2b) and heat shock proteins (HSP17.8, HSP26.7, HSP70, and HSP90.1-b1), which could be also further enhanced by the application of exogenous MI. The present study demonstrated the positive role of MI in mitigating heat-induced leaf senescence in creeping bentgrass associated with improved antioxidant enzyme activities, the accumulation of non-ezymatic antioxidants and sugars, and the expression level of HSFs and HSPs. However, the underlying molecular mechanisms by which the MI improves thermotolerance still deserve further in-depth study.