Study On The Difference Of Anti-freezing In Physiological And Molecular Mechanisms Of Weak Springness Wheat Cultivars During Wintering Period

Physiological mechanism on the difference in the antifreezing tolerance among weak springness wheat cultivars with different sowing dates was investigated in this paper.The processes of young spike development,the contents of antifreezing materials(soluble sugar,soluble porteins,proline,ascorbic acid and glutathione),and the expression of four protective enzyme(glutathione reductase, ascorbate peroxidase,catalase,superoxide dismutase genes) were measured under natural chilling current stress conditions,the main results were as follow:1.The processes of wheat young spike development were closely related to antifreezing tolerance,and the quicker development process of spike,the more serious freezing damage the wheat plant suffered during chilling current.For example,in the first sowing dates(2005-10-05),the quicker development processes of young spike between Yumai 34 and Zhengrnai 9023 cultivars had reached to the late and initial stages of floret differentiation,respectively,and there appeared more serious freezing injury on the two cultivars during chilling current.The freezing mortality of young spikes of these cultivars at two processes were to 96%and 73%,respectively.The processes of wheat young spike development of Yanzhan 4110 cultivar reached to the late stage of two prisms before this chilling current,and the freezing mortality of young spikes was to 25%.The slower development processes of young spike in Yunong 949 cultivar had only reached to the initial stage of two prisms,and there appeared slight freezing injury at the tip of leaves.In addition,there were differences in freezing injuries of young spikes with the same developmentl processes.For example,the development processes of wheat young spikes betweenYanzhan 4110 in the first sowing dates and Yumai 34 in the second sowing dates reached to the same stage(initial stage of floret differentiation), but the freezing mortality rates of spikes in the former were 25%,but there apperaed only slight freezing injury at the tip of leaves in the latter cultivar.The results showed that genetic traits may be also related to freezing resistance of wheat cultivars.2.Before,during and afer chilling current in 2005 winter season.,the contents of soluble sugar,soluble portein,AsA in Yumai 34 plants with the quicker development processes of young spikes and more serious freezing injury were lower than those of Yunong 949 and Yanzhan 4110 with the slower development process of spikes.These result showed that they could be used as indexes to detect the freezing resistance of wheat plants.During chilling current,the contents of Pro and GSH in the leaves of four wheat cultivars with the different sowing dates sharply increased but the contents of them in the leaves of Yumai 34 plants with the quicker development processes of young spikes were higher than those of Yunong 949 and Yanzhan 4110 with the slower development process of spikes.The result implied that Pro and GSH could hardly reflect freezing tolerance of wheat cultivars.3.cDNA fragments of four protective enzyme genes(GR,APX,SOD,and CAT) were cloned from wheat leaves.Their expression in leaves of the above wheat plants before,during and after chilling current was investigated by semi-quantitative RT-PCR.The result showed that the transcript levels and the increasing amplitude of APX and SOD genes were higher in Yunong 949 and Yanzhan 4110 with slower development processes of spikes with slight freezing injury than those with quicker development processes,indicating that they could be used as the indexes to measure the freezing tolerance of wheat plants.The transcript levels of GR genes slightly increasd in all checked wheat plants,but its transcripts in Yumai 34 and Zhengmai 9023 cultivars with the quicker development process of spikes and more serious freezing injury were higher than those with the slower development process of spikes in Yunong 949 and Yanzhan 4110 cultivars.There appeared little changes and difference in transcript levels of CAT gene in all the checked plants.These results suggested that the changes in transcript levels of GR and CAT genes could not be suitable as the indexes of the freezing tolerance among wheat cultivars.In summary,the antifreezing tolerance of wheat plants was closely related to the development processes of young spikes.The slower development process of spikes, the stronger antifreezing tolerance of wheat plants there appeared during chilling current.The contents of soluble sugar,soluble porteins,AsA and the transcript levels of APX and SOD genes in plant leaves with the slower development process of spikes were higher than those with quicker development processes of spikes.These materials could be used as the indexes of the freezing tolerance of wheat.But the contents of Pro,GSH and the transcript levels of GR gene in plant leaves with the slower development process of spikes were lower than the latter,and there appeared little changes and differences in transcript levels of CAT gene in all the checked plants. These could not be suitable as the indexes of the freezing tolerance among wheat cultivars.