Identification On The Cold Resistance In Hybrids Of Populus Deltoids×Section Tacamahaca

Low temperature is one of the most important environmental factors limiting the growth and distribution of plants. Poplar is an important afforestation and greening tree species in Northern China. However, periodic cold injury and its damagement have been resulted in some serious problems to the development.of poplar industry. Therefore, it is necessary to study physiological and biochemical response of different cultivars to low temperature. It was significant to elaborate the mechanism of cold resistance, distinguish the adaptability of different cultivars and the construction of the ecological environment in Northern China.In this paper, the hybrids of Populus deltoids×Section tacamahaca were selected to identify the cold resistance by investigating on the changes of physiological indexes under different temperature. In addition, effects of Calcium signal system on the cold resistance physiological mechanisms were investigated. The main results were as followed:1. According to the comparison of dehydration rate, LT50, MDA and soluble protein contents, SOD and POD activities, the results showed that there were obvious cold resistance differences among those hybrid clones. The sequence of cold resistance in nine hybrid clones was as follows: 07-69 × P.cathayana 1 > 06-69 × P.purdomii 1 > 06-57 × P.szechuanica 1 > Zhongsui 12 > 07-Westda-zhai × P.purdomii 1 > Shaanxi NO.4 > 08-69 × P.cathayana 2 > 08-69 × P.cathayana 4 > E24-01. 07-69 × P.cathayana 1 showed the best cold resistance to cold stress of all the hybrid materials, which belonged to the cold resistance clone. The E24-01 clone material showed the worst resistance to cold stress. The differences of LT50 among the nine hybrid clones were obvious, and it would provided a theoretically support for the breeding of poplar.2. Compared to others clone materials, the hybrid material of 07-69×P.cathayana 1 showed a better adaptability for low temperature stress which prepared lower dehydration rate, LT50, MDA content and higher SOD activity, POD activity, soluble protein content. The change trend of the SOD activity, POD activity and soluble protein content were basically same to the change of temperature, while the content of MDA had a curve just like a converse ‘S’ in terms of its content.3. Based on the effect of different Ca2+ concentration on cold resistance in hybrids of Shaanlin NO.4 and 07-69 × P.cathayana 1 under low temperature stress, we found that 5~15mmol/L Ca2+ treatment could significantly strengthen the cold resistance of poplar compared to higher Ca2+ treatment, 10 mmol/L Ca2+ treatment could extermely decrease membrane injury rate and MDA content, while increase SOD and POD activities and soluble protein content. Exogenous Ca2+ could effectively improve the cold resistance of poplar seedlings and alleviate the damage caused by low temperature stress.4. By addition of Ca2+ chelating agent EGTA or calmodulin antagonist TFP on Shaanlin NO.4 and 07-69 × P.cathayana 1, internal exogenous calcium could strengthen the cold resistance of poplar compared to the Ca-deficient treatment. However, the mechanism of adjusition to the cold stress was inhibited. Consequently, it is suggested that the calcium signal system may be involved in the membrane lipid peroxidation, protective enzyme system and osmotic system in hybrids of Shaanlin NO.4 and 07-69 × P.cathayana 1 under low temperature.5. According to the research on the cold resistance in the hybrid of Shaanlin NO.4 under calcium salts treatment(Ca(NO3)2, CaCl2, Ca(Ac)2), the results showed that calcium salts treatment could effectively decrease membrane injury rate, LT50 and the accumulation of MDA, increase the activities of antioxidant enzyme and the content of osmotic substances, enhance the cold resistance of poplar and alleviate the damage caused by low temperature stress. The ability of cold resistance was been improved under different type of calcium salts, the sequence was as follows: CaCl2 > Ca(NO3)2 > Ca(Ac)2.