Effects Of Salt And Alkali Stress On Physiological Metabolism In Germination And Seedlings Of Cucumber

Salt and alkali stress is one of important environmental factors limiting agriculture production. In this paper, according to the problem of the soil secondary salinization increasingly serious, Effects of salt and alkali stress on physiological characteristics in germination and seedlings of cucumber were investigated, the main results as follows:1. Effects of NaCl stress on damage and reflectance characteristics of two cucumber cultivars was evaluated. The results indicated that'Xintai Mici'was more tolerant to NaCl stress than'Jinyou 1'. NaCl stress significantly increased cucumber leaf reflectance in the spectra of visible light, and the increase degree was higher in cultivar'Jinyou 1'than in cultivar'Xintai Mici', especially in the spectra of green light. Chlorophyll contents, carotenoid contents and xanthophyll cycle pool calculated from reflectance were closely related with the salt damage degree of the cucumber and its tolerance to salt stress.2. The cucumber seeds in germination were treated with different concentration (0, 25, 50 and 100 mmol·L-1) of NaCl and NaHCO3. The results showed that with increasing stress intensity, the germination rate, germination index, vigour index, radicle length, fresh weight and first class lateral roots number were all dramatically decreased, and the inhibiting degree of NaHCO3 treatment were greater than NaCl treatment. With increasing stress intensity, the soluble protein content increased, the activities ofα-amylase, total amylase, and dehydrogenase activities significantly decreased. Furthermore, the changing range under NaHCO3 stress were much greater than under NaCl stress. Both NaCl and NaHCO3 stress significantly inhibited CAT acitivity. Under lower concentration, the activities of POD, APX and SOD elevated with increasing stress intensity. But when the stress intensity continued to ascend, the activities of APX and SOD decreased.3. By a solution culture experiment, the cucumber seedlings were treated with different concentration (0, 25, 50 and 75 mmol·L-1) of NaCl and NaHCO3. The results showed that the cucumber shoot and root growth, chlorophyll content and relative water content (RWC) in leaves were dramatically decreased with increasing stress intensity, but the decrease extents under NaHCO3 treatment were greater than those under NaCl treatment. With increasing stress intensity, the content of Na+ in cucumber shoots significantly increased, while the absorption quantity of K+ reduced, thus, both NaCl and NaHCO3 treatment showed lower K+/Na+, especially under the NaHCO3 treatment. Compared with NaCl treatment, under NaHCO3 stress, MDA, Pro and soluble sugar content in cucumber leaves increased much greater. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR) in cucumber leaves were obviously induced by both salt treatments, while the activities of guaiacol-peroxidase (POD) significantly decreased.