Physiological And Biochemical Changes Of Chinese Cabbage Under Temperature Stress

Chinese cabbage, one of the major vegetable crops in China which is native to North China, is strictly restricted by temperature in its growth and development process, not endure to high temperature, resistant to cool but not to cold. High temperature and cold stress have become the main factors that affect Chinese cabbage's growth, quality and limit their yield and promotion. This paper mainly focus the effects of these two factors on physiology and biochemistry indexes and analysis the photosynthesis changes under these factors by chlorophyll fluorescence kinetics. This paper summarized damage mechanism of temperature stress and analyzed the adaptability to temperature stress of Chinese cabbage. which can provide an important reference in cultivation and breeding of Chinese cabbage.Two common cabbages, Tianjin Qingmaye and 38-days cabbage, were chosen as materials in this experiment. The seedlings of cabbages were cultivated in plant chamber and treated at 5-leaf to 7-leaf stage with artificial climate box for accurate high temperature and low temperature. High temperatures of heat treatment were 30?, 35?, 40?, 45?, 50?, compared with 25? as control. Low temperatures of cold treatment were 15?, 10?, 5?, 0?,-5?, compared with 20? as control. Treatment duration were 2 hours in every stress temperature, and then the physiology and biochemistry indexes were determined immediately. The main results are as follows.Tianjin Qingmaye showed more mild symptoms of heat injury at 45? compared with 38-days cabbage which showed obvious symptoms of heat injury at 35?. The results of chlorophyll content, membrane permeability and MDA content also certified the conclusion that Tianjin Qingmaye appeared obvious symptoms of heat injury under ? 45?, but the 38-days cabbage showed obvious symptoms of heat injury under ? 30?. Along with the decreasing temperature, there is not obvious symptom of cold injury in Tianjin Qingmaye under ? 0?. While the 38-days cabbage appeared obvious symptoms of cold injury at 0?. Similar results also found in MDA content and membrane permeability test.These two cabbages showed some physiological and biochemical adaptive changes under temperature stress. soluble protein content, soluble sugar content and proline content of these cabbages increased under high temperature compared with control temperature, which have certain protective effects for these cabbages under high temperature. The POD activity and SOD activity of Tianjin Qingmaye showed an adaptive increase under mild and moderate high temperature stress. However POD activity and SOD activity of 38-days cabbage were all lower than control condition, which maybe the reason that 38-days cabbage is sensitive to high temperature. Soluble protein content and soluble sugar content of these cabbages stayed relatively stable under low temperature, but the proline content and the activities of POD and SOD showed decreasing trend along with the decreasing temperature of cold stress, which indicated that these osmotic protective substances and antioxidant enzymes were not the key mechanism of cabbages adapting to cold stress. Cold tolerance mechanism of cabbage still need further research.Photosynthesis is the most important biological function of plants and photosynthetic capacity is an important index to measure the resistance of plants. The results of net photosynthetic rate showed that photosynthetic rate were decreased in line with increased temperatures in two cabbages. However, the net photosynthetic rate of two kinds of cabbage were relatively stable(measured at room temperature) under cold stress until to-0?. But photosynthetic system of two cabbages was significantly damaged and photosynthetic rate plummeted to zero at-5?.It is more sensitively to detect the photosynthetic function using chlorophyll fluorescence kinetics technology. Under high temperature stress these cabbages showed common characteristics in chlorophyll fluorescence kinetics curves that J phase and P phase decreased significantly and presented a significant K phase at 45? and 50?. Most of chlorophyll fluorescence kinetics parameters were sensitive to high temperature, in which Tfm, Sm, and N increasd with rising stress temperature, but the RC/CSO decreased. The four above parameters are most sensitive to high temperature, which change significantly at only 30?. The other parameters change obviously at ? 40?. The common rule of these parameters in the two kinds of cabbage was that d VG/dto, d V/dto increased dramatically, ?Po, ?Eo and ?Ro reduce continuously and ?Do increased steadily under high temperature, which showed a slower the electron transfer rate and more heat dissipation under heat stress. Heat stress also significantly damaged the PSII structure resulted an increase of photosynthetic activity of a single reaction center, while a sharp decline in photosynthetic activity per cross section. Ultimately, structure function index(SFI) and performance index(PI) decreased of the two cabbage declined significantly under high temperature. At 45? and 50? high temperature stress, SFI and PI of Tianjin Qingmaye are significantly better than that of the 38-days cabbage which also prove the former has better heat resistance than the latter. But two cabbages treated by 45? and 50? high temperature had lost the assimilating function of CO2.The influence of low temperature stress on the two cabbages in chlorophyll fluorescence kinetics curves mainly reflected on J phase, I phase and P phase, of which J phase was most sensitive to low temperature, and increased significantly with decreasing temperature. While the I phase and P phase declined with the decreasing temperature. At same time the two cabbages present a slightly K phase at-5?, which demonstrate-5? leading to dissociation of the oxygen evolving complex partial from PSII. In the chlorophyll fluorescence kinetics parameters which sensitive to cold temperature stress, Tfm and Vj enlarged with declining temperature, but the ?E, ?Eo gradually declined. Fv/Fm reduced significantly at-5? in both cabbages, illustrated that PS? structures were destroyed and photosynthetic function decreased. In the temperature range of 0?-10?, Tianjin Qingmaye increase the RC / CSO to adapt to low temperature, but 38-days cabbage had no this adaption mechanisms. The results of SFI and PI revealed that Tianjin Qingmaye had no freezing injury at above 0? low temperature stress, while SFI and PI of 38-days cabbage declines dramatically at only 10?, which prove that the Tianjin Qingmaye has stronger cold-resistant power than 38-days cabbage.The results above suggest that the two Chinese cabbage can not endure high temperature. endure low temperature, but can not survive freezing. Tianjin Qingmaye has better resistance to high temperature and low temperature stress than 38-days cabbage. Compared with the physiological and biochemical indexes, the chlorophyll fluorescence kinetics technology are more sensitive and accurate in detecting the tolerance of cabbages to high temperature and low temperature stress, which is an ideal way to study the resistance of Chinese cabbage.