Effect Of Salicylic Acid And Calcium On Tolerance To Low Temperature And Light Intensity In Cucumber Seedlings

For researching the mechanism of calcium(Ca) and salicylic acid (SA) on chilling tolerance in cucumber seedlings, the effects of calcium and salicylic acid on photosynthesis, antioxidase system and osmoregulation system were investigated with'Jinyou No.3'as materials, The main results were as follows:1. Photosynthetic rate (Pn), stomatal conductance (Gs), the rate of transpiration (Tr), actual photochemical efficiency of PSⅡ(ΦPSⅡ), maximal photochemical efficiency of PSⅡ(Fv/Fm) of cucumber seedlings all decreased, but the intercellular CO2 concentration (Ci) increased under low temperature and light intensity. These data suggest that non-stomatal limitation is the main cause of the decrease of Pn in cucumber seedlings during stress period.2. Low temperature and light intensity led to increase in malondialdehyde (MDA) content and superoxide dismutase (SOD) activity, decrease in catalase (CAT) activity. However, peroxidase (POD) activity enhanced at first, whereas reduced at latter two days during stress period.3. Spraying 0.5~2.5 mmol·L-1 SA on the leaves of cucumber seedlings before exposure to stress condition, the Pn, Gs, Tr,ΦPSⅡ, Fv/Fm, and activities of SOD,POD,CAT in cucumber seedlings were higher than those of CK with various degrees, but Ci and MDA content were lower than those of CK, suggesting that SA could modulate the photosynthetic function of cucumber seedlings availably and increase the tolerance against low temperature and light intensity, and the optimum concentration of SA should be 1 mmol·L-1.4. Pretreated with 1 mmol·L-1 SA (SA treatment), 10 mmol·L-1 CaCl2 (Ca treatment), 1 mmol·L-1 SA combined 10 mmol·L-1 CaCl2 (SA+Ca treatment), the Pn increased significantely. SA, Ca, and SA+Ca decreased electrolyte leakage, MDA and H2O2 contents, and osmotic potential, while increased ascorbic acid and glutathione contents, and antioxidants enzymes activity. SA, Ca, and SA+Ca also led to accumulate in soluble sugar, protein and proline largely, therefore, increased the tolorance to low temperature and light intensity in cucumber seedlings.5. No significant differences in improvement of tolerance to low temperature and light intensity among SA, Ca, and SA+Ca treatments were observed.