| Located in the northeastern part of China, Heilongjiang province possesses a long winter period with average temperatures between-20to-30℃. In this circumstance, safe hibernation of winter wheat becomes a historical problem in wheat breeding. Investigation on change features of physiological indices relating to the winter wheat cold resistance during hibernation is therefore of the utmost importance. Plasmalemma is generally viewed as the first line of defense of plants in cold stress, as generation of reactive oxygen at cryogenic temperatures is able to induce membrane lipid peroxidation and deesterification of phospholipids which subsequently lead to the leakage of cell constituents and cell death. Protective enzymes in the plants are capable of scavenging the reactive oxide species(ROS) generated, while differences of plant plasmalemma composition exist under adversity stress. However no preliminary study was addressed concerning the plasmalemma composition of white wheat of unique cold resistance at low temperatures, as well as the cavenger enzymes of ROS. In responding to this need, the Dongnong winter wheat lowningan outstanding cold resistance was selected for this study, with the Jimai winter wheat22of weak cold resistance as a control. Low temperature treatments(chamber) and open field experiments were carefully designed so as to study the protective enzyme activitiesin winter wheat of different cold resistance at cryogenic temperatures, as well as the relationship between winter wheat injury and its membrane lipid composition. The protective enzymes playing vital role at low temperatures were determined plus the membrane lipid compositions, in order to supply significant information on the study of winter wheat breeding and cold resistance.The results are shown as follows:1.Relatively precise measuring method of tillering nodes conductivity was determined, as tillering nodes of winter wheat should be cut in2mm before measurement of conductivity.2. Conductivity of both plants increased with temperature declination. Under the same experimental conditions, conductivity of Dongnong1was distinctly lower than that of Jimai22. LT50(median lethal temperature) of tillering nodesfor both groups was calculated using the Logistic regression on basis of experimental data, which were-22.4℃for Dongnong1and-14.1℃for the latter.3. During hibernationmalondialdehyde content tented to arise according to the decreasing of temperatures. Content of malondialdehydereached the maximum of74.56μmol/gFW for Jimai22on22th February,2013, and for Dongnong1it was62.32μmol/gFW on7th February,2013. Malondialdehyde content in Dongnong1was constantly lower than that of Jimai22.4. Activities of two protective enzymes DOS and POD ascended with temperature declination. However during the period after15th December,2013SOD activity of Dongnong1was significantly higher than that of Jimai22, while activities of POD for both were nearly similar. Content of two protective species ASA and ASH rose with the decreasing of temperatures. After9th January,2013, ASA content ranged from576.48μg/gFW to641.28μg/gFW which was distinctly higher than that of Jimai22(from388.43ug/gFW to401.97μg/gFW). The Dongnong1was also richer in GSH (charactering the content of glutathione) than Jimai22during deep freeze event.6. At low temperatures, Dongong1contained higher content of unsaturated fatty acid than Jimai22, however in the contrary possessing lower content of saturated fatty acid than Jimai22. For saturated fatty acid, palmitic acid accounted for a large proportion (22-38%within study period), whereas that of the stearic acid only ranged from1%-3%. With respect to the unsaturated fatty acidlinolenic acid accounted for the most proportion (31%-53%). At cryogenic temperaturespalmitic acid content in Dongnong1was not lower than that of Jimai22, when linolenic acidcontent of Dongnong1was higher than that of Jimai22.7. Correlation analysis of the compositionof membrane lipid and protective enzymes with the MDA (after membrane lipid peroxidation) and conductivity of plasmalemma injury was performed as well in this study. Results showed that after one month of deep freeze event, MDA and conductivity exhibited statistical negative significance with the ASA, SOD and POD. When during the same period, MDA and conductivity showed highly positive significance with the content of stearic acid, and negative significance with linolenic acid and oleic acid. |
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