Effect of Low Temperature on Physiological Index of Cold-tolerant Casuarina glauca Clones Evaluation of Physiological Responses and Resistances of Nine Wild Poa to Low Temperature Transformation of Saussurea involucrata sikPIP3 Gene into Tobacco and Evaluation of Transgenic Plant Stress-resistance Influence of Over-expression of the BoFLC3 and AtFT Genes on Floweringtime and Cold Tolerance in Brassica juncea Cold-tolerance and Osmoregulation Mechanism of Walnut Cultivars