Assessing the Effects of High Night Temperature On Rice Photosynthetic Parameters: Involvement of Cellular Membrane Damage and Ethylene Response.

High night temperature (HNT) is known to cause chlorophyll degradation and membrane damage in rice plants. Degradation in chlorophyll decreases photosynthetic rate and damaged membranes can increase respiration rate and decrease the transport of photosynthates produced. We hypothesize that HNT stress induces ethylene-triggered chlorophyll degradation and membrane damage resulting in decreased photosynthesis and increased respiration, thereby decreasing plant grain yield. The objective of this study was to determine if application of the ethylene perception inhibitor, 1-methyl cyclopropene (1-MCP) can minimize HNT stress-induced ethylene-triggered chlorophyll degradation and membrane damage, thereby increasing the rice yield. Plants were subjected to ambient night temperature (ANT) (25 ^oC + 0.5 ^oC) or HNT (30 ^oC + 0.5 ^oC) through use of continuously controlled infrared heaters, starting from 2000 h until 0600 h. The HNT increased chlorophyll degradation (7%) and membrane damage (46%), thereby decreasing photosynthetic rate (6%) and increasing respiration (28%). In addition, HNT also decreased pollen germination (42%) and spikelet fertility (31%), thus decreasing yield (14%). Application of 1-MCP decreased chlorophyll degradation (32%), membrane damage (17%) and respiration (30%), and increased pollen germination (26%), spikelet fertility (41%) and yield (18%) under HNT, compared to untreated plants. Application of 1-MCP decreased chlorophyll degradation and membrane damage, thus increasing the photosynthesis and decreasing respiration. Increased photosynthesis and pollen germination along with decreased respiration due to 1-MCP application increased spikelet fertility, thus rice yield under HNT.