Effects of High Night Temperature and 1–Methylcyclopropene (1-MCP) On Rice Leaf Photosynthetic Rate, Respiration, Pollen Viability and Yield.

Heat stress is known to increase ethylene production, which can cause leaf chlorophyll degradation and membrane damage in rice (Oryza sativa L.) plants. Degradation of chlorophyll is associated with decreased photosynthetic rate, and damage to the membranes is associated with increased respiration and decreased transport of photosynthates produced. The objective of this study was to determine if application of the ethylene perception inhibitor, 1-methyl cyclopropene (1-MCP), can minimize ethylene-triggered chlorophyll degradation and membrane damage under high night temperature (HNT). Plants were subjected to 30^oC day temperature and 22^oC, 24^oC, or 28^oC night temperature, starting from 2000 h until 0600 h.  The 1-MCP was applied at mid-boot stage of the rice plant. Leaf photosynthetic rate, respiration, membrane stability, chlorophyll concentration, pollen viability and grain yield were determined. Our results indicated that plants grown under 28^oC (HNT) had greater chlorophyll degradation and membrane damage. In addition, plants grown under HNT showed decreased leaf photosynthetic rate, pollen viability and yield and increased respiration, compared to plants growth under 22^oC night temperature. The 1-MCP-treated plants showed less chlorophyll degradation and membrane damage, compared to untreated plants grown under HNT. In addition, 1-MCP-treated plants grown under HNT showed increased leaf photosynthetic rate and pollen vibility and decreased respiration, compared to untreated plants grown under HNT. Increased photosynthetic rate and pollen viability and decreased respiration due to 1-MCP application increased rice yield under high night temperature (28^oC).