Nitric Oxide and Abscisic Acid Mediate Heat Stress Tolerance through Regulation of Osmolytes and Antioxidants to Protect Photosynthesis and Growth in Wheat Plants

Nitric oxide (NO) and abscisic acid (ABA) play a significant role to combat abiotic stress. Application of 100 µM sodium nitroprusside (SNP, NO donor) or ABA alleviated heat stress effects on photosynthesis and growth of wheat (Triticum aestivum L.) plants exposed to 40 °C for 6 h every day for 15 days. We have shown that ABA and NO synergistically interact to reduce the heat stress effects on photosynthesis and growth via reducing the content of H2O2 and thiobarbituric acid reactive substances (TBARS), as well as maximizing osmolytes production and the activity and expression of antioxidant enzymes. The inhibition of NO and ABA using c-PTIO (2-4 carboxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and fluridone (Flu), respectively, reduced the osmolyte and antioxidant metabolism and heat stress tolerance. The inhibition of NO significantly reduced the ABA-induced osmolytes and antioxidant metabolism, exhibiting that the function of ABA in the alleviation of heat stress was NO dependent and can be enhanced with NO supplementation.Thus, regulating the activity and expression of antioxidant enzymes together with osmolytes production could act as a possible strategy for heat tolerance.