| A two factorial (Ozone level×variety) study was done in a FACE system (free air ozone concentration enrichment) established in Xiaoji Town, Jiangdu County, Jiangsu Province, China (119°42’0"E,32°35’5"N), during the four wheat growing seasons from2006to2010, to investigate the effects of elevated O3on grain quality and the activity of related enzymes in the plants of different genotypes of wheat. Two levels of O3were ambient level (abbreviated as A-O3) and elevated-O3(50%higher than the ambient level, abbreviated as E-O3). The five tested varieties were Yannong19(strong-gluten wheat), Yangmai16and Jiaxing002(medium-gluten wheat), Yangmai15and Yangfumai2(weak-gluten wheat). The main results were as follows:1. E-O3significantly reduced grain yield by18.73%-25.58%,14.1%-34.5%,10.10%26.20%, and15.38%～24.13%, respectively, during the four growing seasons. The tolerance degree of different winter wheat genotypes to E-O3was different. Yangfumai2was most sensitive to E-O3and had the largest yield loss. Jiaxing002was most tolerant to ozone stress and had the lowest yield reduction. The effects of E-O3on ear number and grain number per ear were not significant. The decrease in yield was mainly caused by reduced1000-grain weight. The average1000-grain weight and grain number per ear were influenced by ventilation time and ventilation volume in different growing seasons. The increase in ventilation time and ventilation volume from booting to blooming in2008increased grain number per ear. However, the increased ventilation time and ventilation volume at grain filling stage in2010decreased the average1000-grain weight.2. The activity of enzymes related to the composition of protein and starch, including GS, GOGAT, SSS, and GBSS were reduced significantly by E-O3. The activity of GS and GOGAT reached its peak at the7th day after anthesis. At this date, E-O3decreased the activity of GS and GOGAT in grain by5.8%-14.5%and2.3%-12.5%, respectively, as compared with the A-O3treatment. The activity of SSS and GBSS increased firstly and then decreased after anthesis, with its peak occurred at the28th day after anthesis. In comparison with the treatment of A-O3E-O3decreased the activity of SSS and GBSS in grain by4.6%-10.8%and6.8%-12.9%, respectively, at this date. The enzyme activity of SBE continuously reached its peak at the7th day after anthesis. After this date, its activity decreased. E-O3decreased SBE activity in grain by3.9%-9.7%in comparison with the treatment of A-O3.3. E-O3significantly reduced the content of amylopectin and total starch, and the yield of protein and starch. Compared with A-O3treatment, E-O3significantly reduced protein accumulation by4.5%-22.7%, amylose accumulation by6.3%-19.4%, amylopectin accumulation by14.1%-27.5%, and starch accumulation by12.7%-26.1%. E-O3increased the content of protein and amylose, but decreased the accumulation of protein and amylase, which was probably caused by decreased accumulation of amylopectin and grain weight.4. Under the ozone stress, unit weight, hardness and flour extraction rate of wheat grain were decreased. The content of wet gluten, peak viscosity, trough viscosity, final viscosity, secback, peak time, pasting temperature, dough development time, dough stability time, the energy area, the resistance to extension, and the ratio of the paste were increased. Sedimentation value, breakdown value, water absorption and degree of softening were decreased by E-O3. E-O3decreased the first processing quality, slightly improved the second processing quality of strong-gluten wheat and medium-gluten wheat, but decreased the second processing quality of weak-gluten wheat grain.5. Although protein content in the grain of strong-gluten wheat and medium-gluten wheat was increased by E-O3, grain yield and the first processing quality decreased significantly. The increase in O3concentration had negative effects on the formation of nutritional quality and processing quality. Grain yield, commercial quality, and economic benefit were consequently decreased by E-O3. |
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