Nitric Oxide and Hydrogen Sulfide Coordinately Reduce Glucose Sensitivity and Decrease Oxidative Stress via Ascorbate-Glutathione Cycle in Heat-Stressed Wheat ( Triticum aestivum L.) Plants

The involvement of nitric oxide (NO) and hydrogen sulfide (H S) in countermanding heat-inhibited photosynthetic features were studied in wheat ( L.). Heat stress (HS) was employed at 40 °C after establishment for 6 h daily, and then plants were allowed to recover at 25 °C and grown for 30 days. Glucose (Glc) content increased under HS and repressed plant photosynthetic ability, but the application of sodium nitroprusside (SNP, as NO donor) either alone or with sodium hydrosulfide (NaHS, as H S donor) reduced Glc-mediated photosynthetic suppression by enhancing ascorbate-glutathione (AsA-GSH) metabolism and antioxidant system, which reduced oxidative stress with decreased H O and TBARS content. Oxidative stress reduction or inhibiting Glc repression was maximum with combined SNP and NaHS treatment, which was substantiated by 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) and hypotaurine (HT), scavengers for NO and H S, respectively. The scavenge of H S reduced NO-mediated alleviation of HS suggesting of its downstream action in NO-mediated heat-tolerance. However, a simultaneous decrease of both (NO and H S) led to higher Glc-mediated repression of photosynthesis and oxidative stress in terms of increased H O content that was comparable to HS plants. Thus, NO and H S cooperate to enhance photosynthesis under HS by reducing H O -induced oxidative stress and excess Glc-mediated photosynthetic suppression.