Abstract:【Objective】The study investigated the dynamic response variations in physiological indices of two different varieties of pomegranate branches subjected to various low temperature stress treatments, with the aim of elucidating the cold resistance traits of the 'Tunisia soft-seed' pomegranate.【Methods】Using 'Yecheng Sour Pomegranate' (cold-resistant) from the main planting area in Xinjiang and the introduced 'Tunisia Soft-seed' pomegranate 1a branches as experimental materials, an artificial simulation of low-temperature environment was employed. The relative conductivity of branches, activities of Superoxide Dismutase (SOD), Catalase (CAT), Peroxidase (POD), soluble proteins, soluble sugars, were observed after low-temperature stress under different conditions (-4°C, -6°C, -8°C, -10°C, -12°C) and durations (6 h, 12 h, 18 h, 24 h, 30 h, 36 h, 42 h, 48 h). Use branches with a freezing time of 0 hours at room temperature as a control. Perform physiological and biochemical analysis on the sample after thawing for 8 hours. The determination of conductivity should be carried out immediately. For the determination of other indicators, the branches should be flash-frozen in liquid nitrogen after marking and then placed in a -80℃ freezer for measurement and retrieval as needed. When conducting branch measurements, select the tough bark part of the branch and perform three repeated measurements. The relative conductivity is measured using the conductivity method. The activity of superoxide dismutates (SOD) was measured using the photochemical reduction method of 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. This aimed to determine the longest tolerance duration of different pomegranate varieties under various low-temperature conditions.【Results】This study used the annual branches of 'Tunisian Soft-seed' pomegranate and 'Yecheng Acid Pomegranate' as experimental materials to study the changes in relative conductivity, SOD activity, POD activity, CAT activity, soluble protein content, and soluble sugar content during the dormancy period, under different low temperature treatments and durations. The correlation analysis of various physiological indicators was conducted, and the following conclusions were drawn:(1) Under different temperature and low temperature stresses, as the temperature decreases, the changes in physiological and biochemical indicators of 'Tunisian Soft-seed' pomegranate and 'Yecheng Acid Pomegranate' are basically consistent, but the rate and magnitude of changes are different. As the temperature decreases, the relative conductivity, SOD activity, POD activity, CAT activity, and soluble protein and soluble sugar content of the annual branches of the two varieties of pomegranate all show an upward trend. From the perspective of the entire low-temperature stress process, the relative conductivity value, soluble protein content, and soluble sugar content of 'Tunisian Soft-seed' pomegranate were higher than those of 'Yecheng Acid pomegranate' to varying degrees under five low-temperature stress treatments, while the SOD activity, POD activity, and CAT activity were lower to varying degrees than those of ' Yecheng Acid pomegranate'. Moreover, the relative conductivity value, soluble protein content, and soluble sugar content increased more than those of 'Yecheng Acid pomegranate', while the increase in SOD activity, POD activity, and CAT activity was smaller than that of 'Citric Acid pomegranate'.(2) Under different time stresses, with the extension of time, the overall trend of physiological and biochemical indicators of the two pomegranate varieties is basically the same, but the rate and speed of change vary among different varieties. With the prolongation of stress time, the relative conductivity value and soluble sugar content show an upward trend; SOD activity, POD activity, CAT activity, and soluble protein content showed a trend of first increasing and then decreasing. From the perspective of the entire low-temperature stress process, the relative conductivity value of 'Tunisian Soft Seed' pomegranate is small, with low SOD activity, POD activity, and CAT activity. The content of soluble protein and soluble sugar is low, and the peak time of SOD activity, POD activity, and CAT activity appears earlier.(3) Based on the analysis of all physiological indicators, the 'Tunisian Soft-seed' pomegranate can 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, ‘Yecheng Acid Pomegranate’can 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 ‘Yecheng Acid Pomegranate’is stronger than 'Tunisian Soft-seed' pomegranate. Provide reference basis for further promotion and application of cold prevention measures for the two varieties.【Conclusion】Pomegranate seedlings of 'Tunisia soft-seed ' could tolerate low temperature stress for more than 48 h at -4℃, 36 h at -6℃, 30 h at -8℃, 18 h at -10℃, and 12 h at -12℃. Whereas 'Yecheng sour pomegranate' seedlings could tolerate low-temperature stress for more than 48 h at -4℃ and -6℃, 42 h at -8℃, 36 h at -10℃, and 30 h at -12℃. 'Yecheng sour pomegranate' was more cold-resistant than 'Tunisia Soft-seed' pomegranate. The cold resistance of 'Yecheng Acid Pomegranate' is stronger than that of 'Tunisia Soft-seed' pomegranate. The cold resistance mechanism is mainly due to the strong anti-oxidation and osmotic regulation ability of branches. The results provide reference and basis for the introduction, introduction, cultivation and popularization of pomegranate in other areas.
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