Study On Physiological Responses Mechanism Of Citrus Medica Under Major Abiotic Stress

Citrus medica is evergreen shrub or arbor, a precious species gathers flower, foliage and fruit ornamental in integral whole belongs to Citrus of Rutaceae, it has a broad landscape application prospect and the needs exceeding the supply. However, the lack of study on the ecological adaptability limits its further extension and application. In view of this, the study used superior C. medica strains which selected independently as experimental material to evaluate its cold resistance, and study its physiological and biochemical responses to low temperature, drought, waterlogging and salt stress, so as to clarify the resistance mechanism, make C. medica play its maximize ecological ad economic benefits, and offer scientific basis for breeding high resitance varities, its promotion and application.The results are shown as follows:1. Study on Cold resistance of different C. medica strainsThe cold resistance of24three years old C. medica strains which have favorable fruit characters was studied by field identification, cell membrane permeability research and cluster analysis; the cold resistant physiological mechansim of ten strains which belong to high cold resistance, medium cold resistance and poor cold resistance respectively were studied under low temperature stress. The results showed that the index of chilling injury was intervenient2.00and3.40, and the range of semilethal temperature (LT50) was-14.84--7.05℃. The cold resistance of24C. medica strains was evaluated by cluster analysis based on index of chilling injury and LT50, Chunjiang4, Chunjiang5, Chunjiang6, Xinshiji9, Xinshiji10and Xiangyuan4had high cold resistance; Chunjiang1, Chunjiang2, Chunjiang3, Chunjiang8, Xiangyuan1, Xiangyuan2, Xiangyuan5, Xiangyuan6, Xiangyuan7, Xinshiji1, Xinshiji3, Xinshiji4, Xinshiji5, Xinshiji6, Xinshiji7and Xinshiji8had medium cold resistance; Chunjiang7and Xinshiji2had poor cold resistance. With the temperature decreasing, the contents of MDA, proline and soluble protein, the activities of SOD increased at first and then decreased. In high cold resistance strains, the contents of MDA was low, the contents of proline, soluble protein, and the activities of SOD were high; on the contrary, in low cold resistance strains, the contents of MDA was high, the contents of proline, soluble protein and the activities of SOD were low.2. Response to Drought Stress of C. medicaWith4years old potted seedlings of C. medica as the experimental material, the physiological and biochemical indexes were determined in different drought times (0,1,3,5,7d) under naturally water deficit stress. The results showed that with the increasing of drought stress intensity, the relative water deficit (RWD) of leaves decreased firstly and increased secondly, the water loss rate decresed, cell membrane permeation, MDA and soluble protein contents increased, proline contents and SOD activities increased at first and then decreased.3. Response to Waterlogging Stress of C. medicaPhysiological and biochemical characteristics of4years old potted seedlings of C. medica after0,29,57,85,113d waterlogging stress were studied. The results showed that in this study, C. medica can endure up to4months of waterlogging stress. During the waterlogging stress process, the chlorophyll a+b, chlorophylla, chlorophyllb, soluble protein and soluble sugar contents, SOD, Ascorbate Peroxidase(APX), Pyruvate decarboxylase (PDC), Alcohol dehydrogenase (ADH) and Lactate dehydrogenase (LDH) activities were increased at first and then decreased; while MDA and proline contents and Peroxidase (POD) activities kept on increasing.Therefore it is probably shown that C. medica can adjust them to the oxygen deficit environment by enhancing photosynthetic ability, accumulating osmotic adjustment material, increasing antioxidant and anaerobic respiration enzymes activities to reduce the damage. This may be the reason of C. medica has high waterlogging resistance.4. Response to Salt Stress of C. medicaA pot experiment was conducted to study the salt tolerance of4years old C. medica seedlings under different levels (0,50,100and150mmol·L-1) of NaCl. The results showed that C. medica can be patient in the100mmol·L-1concentration of NaCl. With the increased of NaCl concentration, the relative electronic conductivity (REC) and malonaldehyde (MDA) contents increased significantly; the soluble sugar and proline (Pro) contents also increased gradually with the increasing of NaCl concentration, but the soluble sugar contents increased insignificantly under50mmol·L-1NaCl concentration; the soluble protein contents and SOD activities decreased after an initial increased,50and100mmol·L-1NaCl promoted the soluble protein contents and SOD activities increase, while150mmol·L-1NaCl inhibited it.