Effects Of Exogenous Polyamines On Phsiological -Biochemical Indexes Of Cucumber Seedlings Under Low Temperature Stress

Cucumber (Cucumis sativus L.), originated from subtropical zone, is a very important vegetable crop of Cucurbitaceae in Cucumis, and has always been considered as one of the important facilities vegetables in recent years. But cucumber is also one of typical chilling-sensitive plants, and very sensitive to low temperature stress, low temperature has been a key limited factor of cucumber protected cultivation at anti-season. Therefore, how to improve the chilling tolerance has become the research emphasis of cucumber cultivation. Ployamines, especially putrescine, spermidine and spermine, have promoting effect on growth, development and putting off senility and also can enhance the stress-resistance of plants. Research about effects of cadaverine on cucumber cold resistance has not been reported. This experiment used ’Changchun mici’(chilling-tolerance) and ’Beijing jietou’ (chilling-sensitive) as materials, measured physiological and biochemical indexes and chlorophyll fluorescence parameters, studied the effects of exogenous PAs (Put,Spd,Spm,Cad) on chlorophyll fluorescence parameters and of exogenous Cad on improving chilling-tolerance of cucumber seedlings under low temperature stress.1. Effect of Put,Spd,Spm on Chlorophyll Fluorescence Parameters of Cucumber Seedlings under low temperature stressCucumber seedlings with two true leaves were sprayed by exogenous PAs (Put,Spd,Spm),then they were stressed under low temperature of 8℃/8℃ (day/night) for three days and rewarmed one day. Effect of exogenous PAs(Put, Spd, Spm) on the changes of chlorophyll fluorescence parameters of cucumber seedlings under low temperature stress was studied. The results indicated that the fluorescent parameters of chlorophyll Fm, Fv/Fm,and Fv/FO appeared to decline and FO appeared to increase.Compared with the control treatment, exogenous PAs(Put、Spd、Spm) could significantly promote the increment of Fm, Fv/Fm, and Fv/F0,whereas decreased F0. The effect of exogenous PAs on cold-tolerance of cucumber is proved again by improving the changes of chlorophyll fluorescence parameters of cucumber seedlings.2. Effects of Exogenous Cad on Physiological-biochemical Indexes of Leaves in Cucumber Seedlings Under Low Temperature StressThe aim of this experiment was to study physiological mechanisms of exogenous Cad enhancing the chilling tolerance of cucumber seedlings by analysing the changes of antioxidant enzyme activities and other physiological-biochemical indexes and chlorophyll fluorescence parameters in cucumber (Cucumis sativus L.) seedlings. Cucumber material ’Changchun mici’(chilling-tolerance) and’Beijing jietou’(chilling-sensitive) was subjected to low temperature of 12/7℃ (day/night) and recovering treatment in the artificial climate chamber. The effects of Cad on the changes in electrolyte leakage rate, malondialdehyde (MDA) contents, soluble protein, soluble sugar, proline, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), ascorbate peroxidase (APX) activities and chlorophyll fluorescence parameters under low temperature stress in the seedling leaves were investigated. Compared with the control treatment, Cad pretreatment could significantly reduce MDA contents and electrolyte leakage by16.30% and15.15%,1 3.13%andl2.54%, whereas increased soluble protein content by 16.99% and11.20%, soluble sugar content by 9.35% and 2.90%,proline content by 20.54% and 17.36%,and promoted the increment of SOD,POD,CAT,APX activities by 9.64% and8.42%,19.83% andl8.97%,31.95% and 41.29%,10.66% and 17.13%,and also could improve changes of chlorophyll fluorescence parameters in cucumber seedlings leaves under low temperature stress. The application of Cad could improve chilling tolerance in cucumber seedlings by decreasing the membrane lipid peroxidation, increasing soluble materials and the activities of antioxidant enzyme.