Physiological and biochemical response of two pomegranate cultivars to low temperatures

Abstract: 【Objective】The study investigated the dynamic variations in physiological indices in two varieties of pomegranate subjected to various low temperature stress treatments, with the aim to elucidate the cold resistance of Tunisia Soft-seed pomegranate.【Methods】Using annual branches of Yechengsuan pomegranate(cold-resistant) from the main planting area in Xinjiang and the introduced Tunisia Softseed pomegranate as experimental materials, artificially simulated low-temperature conditions were employed. The membrane leakage of branches, activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), soluble proteins, and soluble sugars were analyzed after low-temperature stress under different cold temperatures (-4 ℃, -6 ℃, -8 ℃, -10 ℃, and -12 ℃) and durations (6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, and 48 h). The annual branches kept at room temperature served as the control. Physiological and biochemical analyses were performed on the samples 8 hours after cold temperatureexposure ended. The determination of membrane leakage was the carried out immediately. For the determination of the other indicators, the branches were flash- frozen in liquid nitrogen after labelling and then stored in a -80℃ freezer for upcoming measurements. The tough bark part of the branch was sampled and three replicated were set for each measurement. The membrane leakage was measured using the electricity conductivity method. The activity of superoxide dismutates (SOD) was measured using the photochemical reduction method with nitrogen blue tetrazole (NBT). The peroxidase (POD) activity was measured using the guaiacol method. The activity of catalase (CAT) was measured by UV absorption method. The soluble protein content was determined using the Coomassie Brilliant Blue method. The soluble sugar content was determined by the anthrone colorimetric method. Correlation analysis among various physiological indicators was conducted.【Results】The result showed that as the temperature decreased the change patterns of physiological and biochemical indicators of Tunisian Soft- seed pomegranate and Yechengsuan pomegranate were basically the same, but the rate and magnitude of changes were different. As the temperature decreased, the membrane leakage, SOD activity, POD activity, CAT activity, and soluble protein and soluble sugar contents in the annual branches of the two varieties all showed an upward trend. Throughout the low-temperature stress treatment, membrane leakage, soluble protein content, and soluble sugar contents in Tunisian Soft- seed pomegranate were higher, while the SOD activity, POD activity, and CAT activity were lower to varying degrees than in Yechengsuan pomegranate. Moreover, membrane leakage, soluble protein content, and soluble sugar content increased at a higher magnitude than those of Yechengsuan pomegranate, while the increase in SOD activity, POD activity, and CAT activity was smaller than that of Yechengsuan pomegranate. With the extension of cold exposure time, the overall change trends of physiological and biochemical indicators of the two pomegranate varieties were similar, but the rate and speed of change varied between the varieties. With the prolongation of stress time, membrane leakage and soluble sugar content showed an upward trend; SOD activity, POD activity, CAT activity, and soluble protein content showed a trend of first increasing and then decreasing. Throughout the experiment, membrane leakage of Tunisian Soft- seed pomegranate was small, with low SOD, POD, and CAT activities. The contents of soluble proteins and soluble sugars were low, and the peak of SOD activity, POD activity, and CAT activity occurred earlier. Based on the analysis of all physiological indicators, the Tunisian Soft-seed pomegranate was able to withstand low temperature stress for more than 48 hours at -4℃, 36 hours at -6℃, 30 hours at -8℃, 18 hours at -10℃, and 12 hours at -12℃. However, Yechengsuan pomegranate could withstand low temperature stress for more than 48 hours at -4℃ and -6℃, 42 hours at -8℃, 36 hours at -10℃, and 30 hours at -12℃. The cold resistance of Yechengsuan pomegranate is stronger than Tunisian Soft-seed pomegranate.【Conclusion】Yechengsuan pomegranate is more cold- resistant than Tunisia Soft- seed pomegranate. The stronger cold resistance in Yechengsuan pomegranate is related to its stronger anti-oxidation and osmotic regulation ability. The results provide reference for the introduction, introduction, cultivation and popularization of pomegranate in other areas.