Sdudy On The Light Drought Stress-induced Cold Resistance Of Cucumber Plants

The purpose of this paper is to verify the influence mechanism of soil moisture on the chilling tolerance in cucumber. The effects of soil moisture for 80 %~90 %(T1), 70 %~80 %(T2), 60 %~70 %(T3), and 50 %~60 %(T4) on the photosynthesis, reactive oxygen scavenge system and osmotic adjustment system of cucumber(Cucumis sativa L. cv.?Jinyou 35?) seedlings and fruiting period plants under low temperature(day/night temperature 8 ℃/5 ℃) were investigated, with 80 %~90 % moisture and normal temperature treatment as the control. The main results were as follows:1. The chilling injury indexes of cucumber seedlings were lowest in T2 and T3, and highest in T1; the electrolyte leakage(EL) were lowest in T2 and T3, and the highest in T4 under chilling stress. The chilling injury indexes of cucumber plants in fruiting stage were also lowest in T2 and T3, and highest in T1; whereas, the EL were lowest in T2 and T3, and the highest in T1. These data suggest that reduced soil moisture appropriately(60 %~80 %) enhanced the chilling tolerance of cucumber. However, long term severe drought stress synergistic effect with chilling stress, and aggravated the injury in cucumber membranes. The cucumber plants in fruiting stage showed higher drought tolorance than that in seedling stage.2. Chilling stress led to significantly decrease in photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), activities of Ribulose 1,5-bisphosphate carboxylase /oxygenase(Rubisco) and Rubisco activase, actual photochemical efficiency of PSⅡ(ΦPSⅡ), maximum photochemical efficiency(Fv/Fm), the antenna transformation efficiency(Fv?/Fm?), whereas increase in intercellular CO2 concentration(Ci) and initial fluorescence(F0) in cucumber seedlings and fruiting period cucumber plants. T2 and T3 showed the least reduction in Pn, Gs, Tr, activities of Rubisco and RCA, ΦPSⅡ, Fv/Fm and Fv?/Fm?, and the least increase in Ci and F0, however, the up or down range of T1 and T4 in photosynthetic parameters were much more under chilling stress.3. MDA content of T2 and T3 were the lowest and T4 the highest among the four treatment. On the contrary, T2 and T3 showed the highest activities of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), ascorbate peroxidase(APX) and glutathione reductase(GR), and as well as the contents of ascorbic acid(As A) and glutathione(GSH); while those of T1 and T4 were significantly lower under chilling stress.4. Low temperature stress decreased the relative water content, water potential and osmotic potential significantly, while increased proline and soluble sugar contents. T2 and T3 cucumber plants showed a significant lower decrease degree in relative water content, water potential and osmotic potential, while high increase degree in proline and soluble sugar contents, in comparison with other treatment plants.5. Light drought induced chilling-tolerance in cucumber plants. The dominant mechanism might be:(1) The observed increase in scavenging ability of active oxygen by enhanced the antioxidant enzyme activities and antioxidant content, increase in the photosynthesis adaptability of cucumber under low temperature, and consequently alleviation in low temperature photoinhibition.(2) Enhanced the osmoregulation ability, maintained higher water potential and osmotic potential, and increased the water absorption and holding capacity.