SALT STRESS-INDUCED RESPONSES IN CUCUMBER PLANTS

A previous study of the formation and removal of reactive oxygen speci es (ROS) in plants in relation to salt stress gave heterogeneous resul ts that depended upon the mode of plant treatment, the age of the plan t tissue and organs, and the experimental setup. This report demonstra tes the relationship between ROS scavenging activities and the degree of damage sustained by cucumber plants under salt stress, in a standar dized assay system. Cucumber seedlings were grown in a hydroponic solu tion for 1 to 2 weeks prior to salt treatment. NaCl or KCl was added t o the solution at a final concentration of 100 mmol/L, with root expos ure to the salt being direct and homogeneous. Plant treatment with NaC l for 4 days resulted in reduced growth, increased leakage of solutes from the leaf tissue and modification of chloroplast structure. NaCl t reatment increased the activities of the antioxidative enzymes catalas e and glutathione reductase, and the content of the antioxidants ascor bic acid and reduced glutathione, but did not affect the activity of s uperoxide dismutase (SOD). The distribution of Na+ and K+ ions in the plant suggests that the salt-derived. injuries and the effects on anti oxidative systems reflect a response to osmotic stress.