Hydrogen Sulfide, Ethylene, and Nitric Oxide Regulate Redox Homeostasis and Protect Photosynthetic Metabolism under High Temperature Stress in Rice Plants.

Rising temperatures worldwide due to global climate change are a major scientific issue at present. The present study reports the effects of gaseous signaling molecules, ethylene (200 µL L -1 ; 2-chloroethylphosphonic acid; ethephon, Eth), nitric oxide (NO; 100 µM sodium nitroprusside; SNP), and hydrogen sulfide (H 2 S; 200 µM sodium hydrosulfide, NaHS) in high temperature stress (HS) tolerance, and whether or not H 2 S contributes to ethylene or NO-induced thermo-tolerance and photosynthetic protection in rice ( Oryza sativa L.) cultivars, i.e., Taipei-309, and Rasi. Plants exposed to an HS of 40 °C for six h per day for 15 days caused a reduction in rice biomass, associated with decreased photosynthesis and leaf water status. High temperature stress increased oxidative stress by increasing the content of hydrogen peroxide (H 2 O 2 ) and thiobarbituric acid reactive substance (TBARS) in rice leaves. These signaling molecules increased biomass, leaf water status, osmolytes, antioxidants, and photosynthesis of plants under non-stress and high temperature stress. However, the effect was more conspicuous with ethylene than NO and H 2 S. The application of H 2 S scavenger hypotaurine (HT) reversed the effect of ethylene or NO on photosynthesis under HS. This supports the findings that the ameliorating effects of Eth or SNP involved H 2 S. Thus, the presence of H 2 S with ethylene or NO can enhance thermo-tolerance while also protecting plant photosynthesis.