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.