Responses of Photosynthetic Efficiency and Ascorbate Peroxidase Induced by Salt Stress in Rice (Oryza sativa L.)

We investigated changes in photosynthesis and activity of ascorbate peroxidase (APX) that scavenges ROS as responses to oxidative stress induced by salinity in rice (Oryza sativa L.). Photosynthetic effi-ciency of rice leaves, monitored in terms of Fv/Fm, declined with the increase of salt concentration (100-300 mM NaCl). Salinity caused an increase of H 2 O 2 in leaves of rice, with an increase of APX activity. Among total APX isoforms, an isoform of stromal-APX 1 in leaves of rice was completely inactivated by 300 mM NaCl, but was not affected by chilling or drought. The results suggest that salt stress acts in quite a different mechanism in relation to the activity of stromal-APX from that of other stresses such chilling and drought. We carried out RT-PCR for analysis of genes expression of APX isoforms as affected by salt stress. The expression of cytosolic APX / thylakoid-bound APX genes in leaves of rice exposed to salt stress was increased, while stromal APX gene expression rap-idly declined