The Response Of Rice Grain Quality To’ Ozone Stress And Its Regulation Factors

The increasing concentration of ground-level ozone changes the environment for crop growth,which eventually affects yield and quality.Ozone stress significantly decreased grain yield,but it’s effect on rice quality were rarely reported.A limited number of studies have indicated that the rice quality showed a trend of deterioration in response to ozone stress,but whether the negative effects of ozone could be regulated by the cultivation strategies or changed with grain position on a panicle was unclear.This study was conducted by using a solar-illuminated gas fumigation platform to investigate the effects of rice varieties(Experiment 1)and nitrogen applications(Experiment Ⅱ)on the responses of rice quality to ozone stress.The objective of this study was to provide experimental basis for producing high-quality rice in high ozone concentration environment.Experiment I was carried out with ozone treatments(100 nL L-1,and clean air as control)as the main plots,and the varieties as the split plots.Eight cultivars,Y Liangyou 900,Y Liangyou 1998,Yongyou 538,Yongyou 15,Nanjing 9108,Wuyunjing 27,Huaidao 5 and Yangdao 6 were exposed to ozone throughout the cropping season.At grain maturity,the grains were divided into superior spikelets’(SS),inferior spikelets(IS),and medium spikelets(MS)according to the grain position on the panicle.The appearance,processing,cooking and eating quality and nutritional quality of rice grains were determined.The main results are as follows:1.Ozone stress significantly reduced the brown rice yield by 40.5%,but had no effect on brown rice percentage.Ozone stress reduced the perfect grain percentage by 3.4 percentage points,but increased the green grain percentage and damaged grain percentage by 2.2 and 1.2 percentage points,respectively.2.Average across all the tested cultivars,ozone stress reduced the weight of rough grain or brown rice kernel by about 8%,which was mainly associated with the reduction in the volume of rough grain or brown rice kernel,since no significant change was observed in the density of either rough grain or brown rice kernel.Ozone stress reduced the length,width,and thickness of rough grain and brown rice kernel by 2-3%,but increased the length-to-width ratio by 1-2%.3.Ozone stress significantly reduced the amylose concentration by 6%.For the RVA profile,ozone stress reduced the maximum viscosity,minimum viscosity,breakdown and final viscosity by 4-13%,but increased the setback,peak time and pasting temperature by 1-2%.Ozone stress reduced the enthalpy by 9%and increased the gelatinization peak temperature by 1%,but had no significant effect on other parameters in the DSC curve.4.Ozone stress increased protein concentration by 8.9%,which was mainly associated with the large increase of globulin,prolamin and glutenlin concentration(10-15%),while the increase of albumin was small(5%).Ozone stress decreased the proportion of albumin to total protein content(5%),while the proportion of other protein fractions showed a trend of increase.Ozone stress decreased the protein yield and the yield of each protein fraction to similar extend with the range of 30-40%.Ozone stress decreased the content of total amino acids,essential amino acids and non-essential amino acids by about 12%.The increase of seven essential amino acids was in the range of 11-17%,and nine non-essential amino acids 6-16%.Ozone stress did not change the proportion of essential or nonessential amino acids to the total amino acids.5.Except for B concentration,ozone stress increased the concentration of N,P,K,Ca,Mg,S,Fe,Mn,Cu,and Zn,with the maximum increase of 24%.Ozone stress also significantly increased the phytate concentrations by 6%.In contrast,the contents of all elements were significantly reduced by 28-49%.6.Out of 93 grain quality parameters determined,78 showed significant ozone by cultivar interactions,and 43 showed significant ozone by grain position interactions.In general,the genotypic sensitivity to ozone stress was in the following order:Yangdao 6,Nanjing 9108,Y Liangyou 1998,Y Liangyou 900,Wuyunjing 27,Huaidao 5,Yongyou 15 and Yongyou 538.In terms of differences within grain positions on a panicle,the majority of the grain quality traits showed that the medium and inferior spikelets were adversely affected more by ozone than superior grains.In experiment Ⅱ,Nanjing 9108 was grown at two levels of nitrogen fertilizers representing normal and high N(15 and 22.5 g N m-2),the ozone treatments was as same as in experiment I.The results showed that,except for element concentration,the effects of ozone treatment on rice quality in Nanjing 9108 were basically consistent with the trends found in experiment I.Out of 93 grain quality traits measured,61 showed significant ozone by nitrogen interactions,and 37 showed ozone by grain position interactions.In most cases,high-N-treated rice showed a greater response to ozone stress than that of normal N,and the grain quality of inferior and medium spikelets was affected more by ozone than that of superior spikelets.In summary,elevated ozone concentration deteriorates the appearance quality,processing quality and cooking quality of rice,but the concentrations of protein,protein fractions,amino acids,and elements showed a trend of increase.The effects of ozone stress on rice grain quality were affected by varieties,the grain position on the panicle or the nitrogen fertilization.In most cases,grain quality of rice plants grown with high-N supply was affected more than that of normal-N plants,and grain quality of inferior spikelets were affected more by ozone stress than superior spikelets.