Salt stress-induced responses in cucumber plants

A previous study of the formation and removal of reactive oxygen species (ROS) in plants in relation to salt stress gave heterogeneous results that depended upon the mode of plant treatment, the age of the plant tissue and organs, and the experimental setup. This report demonstrates the relationship between ROS scavenging activities and the degree of damage sustained by cucumber plants under salt stress, in a standardized assay system. Cucumber seedlings were grown in a hydroponic solution for 1 to 2 weeks prior to salt treatment. NaCl or KCl was added to the solution at a final concentration of 100 mmol/L, with root exposure to the salt being direct and homogeneous. Plant treatment with NaCl for 4 days resulted in reduced growth, increased leakage of solutes from the leaf tissue and modification of chloroplast structure. NaCl treatment increased the activities of the antioxidative enzymes catalase and glutathione reductase, and the content of the antioxidants ascorbic acid and reduced glutathione, but did not affect the activity of superoxide dismutase (SOD). The distribution of Na⁺ and K⁺ ions in the plant suggests that the salt derived injuries and the effects on antioxidative systems reflect a response to osmotic stress.