Study On Growth And Physiological Metabolism Of Tomato Seedlings Under High Temperature Stress

With the increasing greenhouse effect, global temperatures continue to rise, horticultural production is facing the problem of high temperature stress. In summer and autumn in southern china, especially in protected cultivation, the abnormal high temperature is occurred frequently. The high temperature stress seriously inhibit the normal growth and development of plants, witch has become the main Constraint of Vegetable production. Therefore, the physiological response of five different tomato varieties to high temperature were studied in this paper, which provide theoretical basis for screening high-temperature cultures.In order to investigate the heat-resistant mechanism of tomato, five different thermotolerance tomato cultures ('2583','Shenfen 8','Puhong 909','Shenfen 998', and 'Fen 2') were used as experimental materials, the varieties of physiological and growth index between varieties at high temperature were studied by comparative analysis. The main purpose of this test is to provide theoretical basis for screening resistant varieties. In this paper, the effect of high temperature on Seed germination, antioxidant defense system and the parameters of photosynthesis and fluorescence were studied, the results are as follows:1. All varieties of high temperature on seed germination rate increased with temperature with reduced processing. The germination of seed was completely inhibited of all tomato varieties at 37℃. the'Puhong 909'was most inhibition by the high temperature, while the'Fen2'was least. High temperature also had a significant inhibiting effect on the early-stage seedling roots but little effect on the shoot length. High temperature led the seedlings'superoxide anion producing rate and MDA content to significantly increase and the SOD, POD and CAT activities were increased.2. The plant height, stem diameter, fresh weight, dry weight and root shoot ratio decreased significantly of five varieties tomato seedlings under high temperature. Well, the electrolyte leakage was increased, and the content of proline and soluble sugar were accumulated. The varieties ('fen 2'and'2583') with less leave damage, which has smaller electrolyte leakage and the osmolyte content of which was higher.3. The superoxide anion (02-·) production rate and malondialdehyde (MDA) content increased significantly in leaves of all varieties tomato under high temperature. The activities of SOD,POD,CAT,APX,GR,MDAR and DHAR were showed the trend that increased firstly and then decreasing. The content of ASA in the leave was significantly decreasing, but the content of DHA was increased, as which the ratio of AsA/DHA was decreased. The content of GSH was increased at first, but later fell sharply, significantly lower than control. Well, the GSSG content was increasing. So the ratio of GSH/GSSG was decreased. The differences between varieties suggest that the tomato seedlings can removal the reactive oxygen effectively by increasing the activities of antioxidant enzymes and the content of antioxidant substances, which alleviated the damage of lipid peroxidation caused by the high-temperature.4. The chlorophyll and carotenoid content was significantly lower than the control. Pn,Gs and Ls of the leave were significantly decreased under the high temperature, while the Ci and Tr was significantly increased. The amplitude between different varieties was different. It showed that high temperatures can cause the pigment degraded and inhibited the photosynthesis of tomato seedlings。The role reason of the decreased of net photosynthesis was not caused by stomatal factors. The seedlings has more thermotolerance has some resistance to high temperature, cause the margin of increase or decrease was both smaller.5. At high temperature condition, the Fo and qN were significantly higher than the control. While Fm, Fv/F0, Fv/Fm, qP and yield were all significantly decreased. The more thermotolerance varieties, the smaller amplitude. It suggested that the PSⅡwas affected by the high temperature, the radio of open part was reduced, the speed of electron transfer was slowed down on electron transport chain, and the photosynthetic efficiency was decreased. The effect on the higher tolerancce varieties was lesser, most of which were reversible.