Effect Of Heat Stress On Photosynthesis And Antioxidant System Of Pepper (Capsicum Annuum L.) Seedling

Four pepper (Capsicum annuum L.) cultivars, Sujiao 5, Jiangshu 2, Jiangshu 4 and Xiangyan 5, with different adaptability to heat stress, were used to study the responses on photosynthetic characteristics and active oxygen. In this study, high temperature was imposed by maintaining the plants at 35℃, 40 ℃, 45 ℃ for 0h, 12h, 24h, 36h and 48h in an environmental plant growth chamber.At the first, the responses on photosynthetic characters and its relation factor, Ci, Gs, Tr, Chl content and water content, were studied. Result showed that leaves had a capability of quick response. Pn decreased quickly after treatment with different temperature and there is a negative correlation between Pn and the time of treatment. Compared non-heat tolerant varieties, Pn in heat tolerant varieties decrease slowly. Gs had a synchronization with Pn before 12h of treatment and then they lost correlation, Ci increased at early stage and then keep a stable level, this showed that the effect of stomatal is mainly occupied to decrease Pn at the early stage and the non-stomatal done at the upper stage. Further there is a negative correlation between Tr and Gs and it easy to understand that the plants tempt to freeze the leaf strength Tr.The second, Effect of heat stress on the content of MDA and the involvement of antioxidant enzyme activities and proline content in the protection against heat-induced oxidative damage. Results showed that, the plants answered with physiological mechanism. MDA content had a continued increase. MDA content is high in heat tolerant varieties and is low in non-tolerant ones, there was a negative correlation between MDA content and the temperature or the time of heat stress. The Effect of heat stress on activities of these oxygen is discrepant. Following the temperature and the time of treatment, SOD activity decreased, CAT and APX activities decrease after a discrepant increase, POD activity had an increased trend. The changes on CAT activity and APX activity are similar. As an important amino acid, high proline content wasfound in heat tolerant variety both under high temperature and at the different stage after treatment.Above all, we can use Pn, MDA content, SOD activity, POD activity and Pro content in pepper leaf as standard valued the capability of pepper under heat stress.