Effects Of Low Temperature Acclimation On Growth And Physiology Of Pepper Seedlings

In order to explore the effects of low temperature acclimation on the growth and physiology of pepper seedlings, this research employed two pepper cultivars, Longjiao No.10(who could bear the low-temperature) and Lawang No.3(who couldn‘t bear the low-temperature), as experimental materials, and climatic cabinates were used to simulated low temperature environment. Indexes like photosynthetic physiology, membrane lipid peroxidation, antioxidant enzyme activity and changes of osmotic adjustment substances in pepper leaves were determined during low temperature acclimation and different simulation environment treatments. There were 6 treatments in this research, including CK1: normal temperature treatments(25℃/16℃, day/night) of Longjiao No.10; CK2: normal temperature treatments(25℃/16℃, day/night) of Lawang No.3; TA1: 5 days low temperature stress treatment of Longjiao No.10(without low temperature acclimation); TA2: 3 days low temperature acclimation(12℃/10℃, day/night) and then 5 days low temperature stress(8℃/5℃, day/night) of Longjiao No.10; TB1: 5 days low temperature stress treatment of Lawang No.3(without low temperature acclimation); TB2: 3 days low temperature acclimation(12℃/10℃, day/night) and then 5 days low temperature stress(8℃/5℃, day/night) of Lawang No.3. The experimental results show that:1. The plant height and stem diameter of pepper seedlings under low temperature stress(8℃/5℃, day/night) were significantly lower than those of CK1 and CK2. The increase extent on plant height and stem diameter of pepper seedlings in TA2 and TB2 which after low temperature acclimation were larger than those of pepper seedlings in TA1 and TB1 which without low temperature acclimation, and had no significant differences when compared with CK1 and CK2.2. After 5 days of low temperature stress(8℃/5℃, day/night), compared with CK1, the net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr) and Fv/Fm and ФPSII of TA1 and TA1 were all significantly decreased. Moreover, the net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr) and Fv/Fm and ФPSII of TB1 and TB2 were all lower than those of CK2. Then, these indexes of TA2 and TB2, which seedlings were domesticated under low temperature, were evidently higher than those of TA1 and TB1.3. After 5 days low temperature stress(8℃/5℃, day/night), then 3 days recovery(25℃/16℃, day/night) and 2 days low temperature stress(8℃/5℃, day/night) again, Pn, Gs, Tr, Fv/Fm and PSII value of TA1, TB1, TA2 and TB2 decreased again. The reduction range of each index from seedlings of TA2 and TB2(with low temperature acclimation) was all significantly less than those of TA1 and TB1(without low temperature acclimation).4. Five days 8℃/5℃(day/night) treatment later, the POD, APX activity, MDA content and cell membrane permeability of seedlings from TA1 and TA2 were markedly higher than CK1; And SOD and CAT activities were lower than CK1. Meanwhile, these indexes of TB1 and TB2 were all significantly higher than those of CK2; And SOD and CAT activities were lower than CK2. POD, APX activity, MDA content and cell membrane permeability of seedlings domesticated 3 days(12℃/10℃, day/night) of treatments TA2 and TB2 were significantly lower than TA1 and TB1 which without domestication; and SOD and CAT activities of TA2 and TB2 were all notably higher than TA1 and TB1.5. After 5 days low temperature stress(8℃/5℃,day/night), then 3 days recovery(25℃/16℃, day/night) and 2 days low temperature stress(8℃/5℃, day/night) again, POD and APX activity, cell membrane penetration and MDA content of TA1, TB1, TA2 and TB2 rose again, activities of SOD and CAT lowered again. And the change extent of seedlings after low temperature acclimation(TA2 and TB2) was remarkably smaller than seedlings without low temperature acclimation(TA1 and TB1).6. Low temperature stress treatment for 5 days(8℃/5℃,day/night) later, the contents of proline, soluble sugar and soluble protein of TA1 and TA2 were significantly higher than CK1. Simultaneously, these indexes of TB1 and TB2 were all significantly higher than those of CK2. Contents of proline, soluble sugar and soluble protein in domesticated seedlings from TA2 and TB2 were all notably less than TA1 and TB1.7. After 5 days low temperature stress(8℃/5℃,day/night), then 3 days recovery(25℃/16℃, day/night) and 2 days low temperature stress(8℃/5℃, day/night) again, the contents of proline, soluble sugar and soluble protein of seedlings from TA1, TB1, TA2 and TB2 rose again, The increase range of each index from seedlings of TA2 and TB2(with low temperature acclimation) was all significantly less than those of TA1 and TB1(without low temperature acclimation).8. After 5 days cold stress(8℃/5℃,day/night), then 3 days recovery(25℃) and 2 days low temperature stress, the increment of plant height and stem diameter of Longjiao No.10(high tolerance with cold) were larger than those of Lawang No.3(low tolerance with cold). And the variation extent of soluble sugar and soluble protein of Longjiao No.10(high tolerance with cold) were larger than those of Lawang No.3(low tolerance with cold). The variation extent of photosynthetic indexes, chlorophyll florescence parameters, cell membrane penetration, the content of malondialdehyde(MDA), proline(pro), and activities of antioxidant enzymes of Longjiao No.10(high tolerance with cold) were less than those of Lawang No.3(low tolerance with cold).