Physiological And Biochemical Change Of Low-Temperature Stress Response In Citrus

The world citrus industry has been restricted greatly by the periodical cold stress. Thus, it is of substantial interest in cold tolerance breeding to reduce the loss. The recent cold resistance researches used the material of in vitro leaves and protoplast mainly, while the transportation and cooperation of signal, hormone and nutrition in the plants are quite different from the field conditions. In order to unravel mechanism underlying the cold tolerance of Poncirus trifoliata Raf. and to facilitate cold resistance breeding, in the cuccrent work difference in the aspects of the damage of cell membrane, the activity of POD and CAT as well as the content of MDA between Poncirus trifoliata Raf. and C. sinensis Osbeck was investigated. In addition, effect of exogenous ABA on physiological and biochemical response of Ponkan in vitro seedlings was examined. The main results are as follows.1. Under cold stress, the membrane injury in Poncirus trifoliata Raf. was less severe than that in sweet orange (Citrus sinensis Osbeck), so were the synthesis of free radicals and the content of MDA. The electric conductivity of ABA-treated leaves was smaller than that of untreated ones under 4℃.2. Compared with C. sinensis, Poncirus trifoliata had higher activity of protective enzymes like POD and CAT, leading to better cold tolerance. During cold stress, acitivities of different protective enzymes exhibited similar change in the two materials, while POD changed more prominent than CAT.3. In addition, the content of MDA varied inversely with the acitivity of the protective enzymes, the materials treated with ABA having much less MDA than the untreated ones, implying that ABA mighh play a role in cold tolerance. The results of SDS-PAGE showed that the expression of some polypeptides was obviously increased. The protein expression of control and treatment were both increased, with ABA protein increased the most. The expression of a 40.5kDa polypeptide was up-regulated by ABA pre-treatment , and slim change was observed in the control of 25℃, indicating that this polypeptidecan be induced by ABA or low temperature .