Effects Of High Temperature,Drought And Their Combination Stress After Anthesis On Expression Of Genes Encoding Enzymes For Starch Biosynthesis In Developing Wheat Grain

Experiments were conducted at the Agricultural and Experimental Farm at Henan Agricultural University, during the 2010-2012 growing season. To evaluate the effect of environment-stress on expression of genes involved in starch biosynthesis in developing wheat grain, a high-yield winter wheat (T. aestivum L.) cultivar currently used in Huanghuai wheat production area of China, Zhengmai 366, was grown by pot experiment in natural environment till flowering. A four-day heat stress treatment (38℃,11:00-16:00) and water stress (soil moisture content 55%) were applied at 8 days after anthesis. During 2010-2011 we investigated the effects of short-term extreme high temperature stress (HT), drought stress (DS) and their combination (HT+DS) on the wheat grain weight and starch content. During 2011-2012 we investigated the influences of different stress treatment on expression of genes encoding enzymes for starch biosynthesis in developing wheat grains. The main results were as follows:1. The results of the effect of different stress treatment conditions on the kernel-filling stage show that:compared with control under single stress grain-filling stage was not obvious difference, while under combination of HT and DS grain-filling stage was shorten six days, grain-filling ceased at 29 days after anthesis. Compared with control, at mature stage HT, DS and their interaction reduced the grain weight by 30.1%,13.2% and 45.6%, respectively. From the grain morphology, HT and DS treatment had a negative effect on grain-filling in wheat, and caused a noticeably smaller grain size at maturity. The test results of grain length, width, and thickness show that, combination of HT and DS had more serious effect on grain-filling than HT and DS, for sole environmental stress, it seemed that effect of DS was smaller than that of HT.2. Adversity stress restrained starch accumulation and made the starch content decreased. At mature stage, compared with control, HT, DS and their interaction reduced the total starch content in grains by 11.5%,9.5% and 28.5%, decreased amylose and amylopectin content by 6.9%,4.8% and 24.1% and 13.2%、10.7% and 29.6%. Under different stress treatment the decrease of amylose content was less than total starch and amylopectin content. As for the stress factors, the influence of HT was greater than DS, combination of HT and DS was more serious than single factor, the difference of treatments was significant. Under different stress conditions, the declines of amylopectin content were greater than amylose content, resulting in a reduction of the amylopectin/amylose as for the control. Interaction of HT and DS had a greater reduction, for sole environmental stress, it seemed that effect of HT was more serious than that of DS.3. During the grain-filling stage the expression of genes related to starch biosynthesis were influenced by HT, DS and their combination. Under HT there were 4 genes up-regulated,14 genes down-regulated and 5 genes not obvious change; under DS there were 8 genes up-regulated,12 genes down-regulated and 3 genes not obvious change while under combination of HT and DS there was 1 gene up-regulated,1 gene not obvious change and the other 21 genes down-regulated. Among those 23 genes related to starch biosynthesis,9 genes were at high expression level during grain-filling stage and played an important role in starch biosynthesis process. Among those 9 genes,8 genes were down-regulated under HT; 6 genes were down-regulated under DS and 8 genes were down-regulated under combination of HT and DS. It will make a serious restrain of the starch synthesis. Synthesize the genes expression under different treatment conditions, it seemed that effect of DS on the expression of genes was slighter than that of HT, interaction of HT and DS resulted in a greater influence of genes expression.As for the change range of the genes expression, compared with control under HT the expression of GBSSI, SSI, SBEI, SBEIIa and SBEIIb were down-regulated by 26.8%,28.9%, 24.7%,13.2% and 32.4%, under DS the expression of them were down-regulated by 20.9%. 9.8%.23.1%,0.2% and 19.4%, while under combination of HT and DS the expression of them were down-regulated by 58.7%,63.6%,50.6%,51.3% and 60.8%. The result indicated that under HT, DS and their combination the range of down-regulation for these genes involved in amylopectin biosynthesis (SS and SBE) were far greater than that of GBSSI. This result coincided with the decrease in the amylopectin-to-amylose ratio, which might further impact the properties and end-use quality of wheat starch. As for the stress factors, the influence of HT was greater than DS on starch biosynthesis, this also confirm with the change of starch content.