Abstract: Two tomato (Lycopersicon esculentum) cultivars with different Ca sensitivity were used to study the effects of exogenous Ca on their root activity,CaM content,chlorophyll a/b ratio,and reactive oxygenscavenging enzymes' activities under different Ca concentrations in nutrient solution.The results showed that the root activity and CaM content of two cultivars increased with increasing Ca concentrations in the nutrient solution.The root activity and chlorophyll a/b ratio of Cainsensitive cultivar Jiangshuyihao were higher than those of Ca－sensitive L₄₀₂ under extreme low Ca stress (1 and 4 mg·L^-1),while lower than those of L₄₀₂ when sufficient Ca was applied (100 mg·L^-1),indicating that Jiangshuyihao had a greater capability to bear the nutrient and light stress under low Ca stress.The SOD activity of Ca－insensitive cultivar Jiangshuyihao under 1 and 4 mg·L^-1 Ca was higher than that of L₄₀₂,while the activities of POD and CAT of L₄₀₂ were consistently higher than that of Jiangshuyihao under test Ca concentrations in the nutrient solution.Comparing with 100 mg·L^-1 Ca in solution,4 mg·L^-1 Ca led to an increase of CAT and POD activities and a decrease of SOD activity in the two cultivars,but the variation of SOD activity was greater in L402 than in Jiangshuyihao,indicating that the system of defence enzymes in Ca-insensitive cultivar played a key role when suffered from Ca stress.

Key words: Sulfur fertilization, Crops, Increase production