Effects of High Night Temperature and Abscisic Acid On Rice Leaf Photosynthetic Rate, Photochemistry, Respiration and Physiology.

High night temperature (HNT) is known to decrease rice yields. The impacts of abscisic acid (ABA) on higher plants have been the subject of many studies. However, little or no work has been carried out on rice responses to ABA under HNT-stress conditions. This study determined the effects of ABA on rice leaf photosynthetic rate (P_N), photochemistry, respiration and physiology under HNT-stress conditions. High night temperature decreased P_N (5%), stomatal conductance (21%), spikelet fertility (5%) and yield (6%) and increased respiration rate (74%) and grain chalkiness (221%). The application of ABA increased P_N (6%) as a result of increased stomatal conductance (18%), quantum yield (8%) and electron transport rate (8%), under HNT. In addition, application of ABA decreased non-photochemical quenching (41%) and respiration rate (33%), under HNT. ABA-treated plants grown under HNT showed increased spikelet fertility (10%) and yield (13%) as a result of increased P_N and decreased respiration.