Abstract: Two cucumber （Cucumis sativus L.）cultivars，'Jinyan 4' (salt tolerant) and 'Jinlü4' (salt sensitive) were grown in nutrient solutions with three NaCl levels（0，25，50 mmol·L-1）for the investigation of plant growth, chlorophyll fluorescence and active oxygen metabolism in seedling leaves. The results showed that NaCl stress decreased plant growth, chlorophyll content, quantum yield of PSII (ΦPSII)，initial fluorescence yield（Fo）and non-photochemical quenching of fluorescence（NPQ）. The plant growth of 'Jinyan 4' was less affected by salt stress than 'Jinlü4' and the photosynthetic apparatus was less injured by salt stress than 'Jinlü4'. However, photochemical efficiency of PSII (Fv/Fm) was not affected by salt stress. Meanwhile，salt stress significantly increased the activity of ascorbate peroxidase (AsA-POD) and significantly decreased superoxide dismutase (SOD) activity in 'Jinlü4'. Free radical producing rate, and H2O2 and MDA content increased with increasing NaCl levels, however, less H2O2 content and lipid peroxidation were observed in the leaves of 'Jinyan 4' than 'Jinlü4'. It is concluded that higher SOD activity, less H2O2 and MDA content may be involved in higher salt tolerance of 'Jinyan 4'.

Key words: NaCl stress, Cucumber（Cucumis sativus L.）, Chlorophyll fluorescence, Active oxygen metabolism