Inductive Effect of Abscisic Acid,Salicylic Acid,and Calcium on Cold Resistance of Cucumber Seedlings

The purpose of this paper is to investigate the effect and its mechanism of abscisic acid(ABA),salicylic acid(SA) and calcium chloride(CaCl2) on cold resistance of cucumber(Cucumis sativus L.) seedlings.Cucumber(cv.Jinyou 35) seedlings pretreated with a foliar spray of 0.1 mmol·L-1 ABA,1 mmol·L-1 SA,10 mmol·L-1 CaCl2,or distilled water(control) were displaced into growth chambers and treated under low temperature(day/night temperature is 8 ℃/5 ℃).The results revealed that low temperature stress significantly increased the chilling injury index,electrolyte leakage(EL),contents of malondialdehyde(MDA) and hydrogen peroxide(H2O2).The peroxidase(POD) activity increased gradually with stress time,whereas,activities of superoxide dismutase(SOD),catalase(CAT),and glutathione reducase(GR) increased at first and reduced later.The contents of proline and soluble sugar enhanced remarkably with stress time.Pretreated with ABA,SA or CaCl2 before exposure to stress condition,the cold injury indexes of cucumber seedlings decreased by 50.0%,40.0% and 47.1%,respectively.ABA,SA and CaCl2 treatment seedlings showed significant lower increase degree in EL and MDA content compared with control seedlings.At the initial stress stage,the increase degree of H2O2 content in ABA,SA and CaCl2 treatment seedlings were higher than that of control,but the H2O2 content in ABA,SA and CaCl2 treatment seedlings trend to reduction after 24 h,and were lower by 27.9%,27.5% and 34.4% respectively at 72 h,compared with that of control.The ABA,SA and CaCl2 treatment seedlings showed significant higher antioxidase activity and contents of proline and soluble sugar than those of control.These data suggest that ABA,SA and CaCl2 can induce cold resistance in cucumber seedlings,and the inductive effect may be related to the observed increase in antioxidase activity and osmoregulation capability.