The Response Of Plasma Membrane NADPH Oxidase To Drought Stress And Its Catalytic Properties In Rice

The plant plasma membrane NADPH oxidase(PM-NOX)has been considered as the primary source of reactive oxygen species such as O₂^·-and H₂O₂ when plants endure a lot of biotic or abiotic stresses.As a new kid on the block of organisms from adverse environmental stresses,PM-NOX has been paid much attention in its gene expression,protein structure, membrane topology,and different homologs under various circumstances,However,the role of PM-NOX and its regulatory mechanism in plant development and stress defences are not clear yet.In the present study,the activity of PM-NOX and its catalytic properties in rice were investigated under different water supply conditions.Drought led to the decrease of the rates of photosynthesis and transpiration,intracellular CO₂ concentration and stomatal conductance as well as the leaf relative water content(RWC).The activities of antioxidant enzymes such as SOD,CAT,POD,APX and GR were also increased by drought.Both increased levels of H₂O₂ and O₂^·-production and increased activity of PM NADPH oxidase were also observed under drought stress.The histochemical analysis showed that severe drought caused the increase of H₂O₂ and O₂^·-production in the leaves of rice and Diphenylene iodinium(DPI),a specific inhibitor of the PM NADPH oxidase,accelerated the accumulation of H₂O₂ and O₂^·-and thus led to more injuries to the droughted leaves.The rice PM-NOX was sensitive to DPI and presented partially flavin-dependent.The activity of PM-NOX can be directly regulated by Ca²⁺.Also we found that the optimum pH and optimum temperature of this enzyme are 9.8 and 35℃in rice, respectively,and drought caused the optimum temperature shifted to 45℃.These results suggest that the PM-NOX involves in the response of rice to drought stress and presented the high-temperature tolerance and the alkaline-philic features.