Time- and tissue- specificity of antioxidant enzyme activity in salt-stressed barley leaves

Soil salinity affects plant photosynthesis due to decreased stomatal apertaure and restricted CO2 availability, thus leads to remarkable increase in ROS concentration, while high reactive ROS could be toxic and give rise to oxidative damage. In this experiment, four major antioxidant (AO) enzymes (SOD, CAT, APX, POD), Na+, K+ and chlorophyll contents were evaluated in TX9425 (salt tolerant) and Naso Nijo (salt sensitive) to investigate their roles in scavenging ROS. Plants were treated with 240 mM NaCl at three and half leaf stage. Enzyme activities were measured from the 2nd and 3rd leaf from the bottom in four leaves stage plants 1, 2, 5, 10 days after salt treatment. Results showed that SOD activity increased in both varieties with no significant differences between tissues (2nd and 3rd leaf). No marked changes were found for CAT, APX and POD in both varieties but the 2nd leaf showed significantly higher POD activity than the 3rd leaf. Naso Nijo showed higher Na+ and Na+/K+ ratio and greater reduction in chlorophyll content than TX9425. It is suggested that AO profiles couldn’t be used to indicate the difference in salinity tolerance between these two varieties.