Grain Yield And Protein Quality In Response To Shading After Anthesis And Nitrogen Regulation In Wheat

Shading after anthesis as a result of cloudy or rainy days and big population density oftenoccurs in the the Huang-Huai-Hai plain of China, and has negative influence on wheat grainyield and quality. In the present study, two different gluten winter wheat cultivars withdifferent subunit compositions, and two different spike-types cultivars were used to evaluatethe effect of shading at different grain filling stages, different shading intensities and nitrogenregulatory measures on changes in wheat grain yield and quality at agronomy, physiology andbiochemistry levels. Information obtained will help to determine the physiology andbiochemistry changes in wheat growth and development and how to alleviate the negativeeffect of shading on wheat development from adjusting the nitrogen application times, whichwill provide a theoretical basis for obtaining higher grain yield and superior grain quality inwheat. The main results were as follows:1The study of changes of wheat grain protein quality at different grain filling stagesShading at different grain filling stage increased the protein content and its componentsat the maturity. The gliadin are more sensitive to shading at early grain filling stage thanshading at other grain filling stages, the content of glutenin increases most to the shading atmiddle shading grain filling stage for two cultivars. The ratio of glutenin to gliadin wasincreased by shading at the early grain filling stage and decreased by shading at the middlegrain filling. This could be explained that the gliadin protein was formed at early grain fillingstages, while the glutenin protein was formed at middle and late grain filling stages.The changes of GMP content during the grain filling showed the "V" model with thelowest content at21DAA for the two cultivars. This may be caused by the lower proteinaccumulation rate than the starch accumulation rate which had dilution effect on the GMPcontent. For the comparison of the two cultivars in the two seasons, the GMP content inJinan17was higher than that in Tainong18in different treatments during the grain filling,especially at the maturity. Shading at different grain filling stages all increased the GMPcontent during the grain filling. The GMP content under shading at early grain filling stagewas higher than shading at middle grain filling stages before and in21DAA and then was lower than shading at middle and late grain filling stages. The proportion (by volume, numberand surface area) of larger granules in GMP was decreased by shading at early grain fillingstage and increased by shading at middle and late grain filling stages. In general, the presentresult suggested that the formation of larger GMP particles was more sensitive to shading atearly grain filling stage and short-term dim light at the middle and late grain filling stageswere helpful to accelerate the hyper-aggregation process and promote the formation of largerGMP granules.HMW-GS accumulation in grain started at about14DAA in Jinan17and Tainong18, theinitial formation time of individual subunits was not influenced by shading at different grainfilling stages, however the content of each it was increased by shading at different grainfilling stages, especially at middle grain filling stage, though the amount per grain of eachindividual subunit was decreased by shading which was due to the decreased grain weight atmaturity. The content and accumulation amount of Glu-A1,Glu-B1and Glu-D1subunitsshowed the increasing trend during the grain filling stages and attained the maximum valuesat the35DAA. The content of Glu-A1subunits of stronger gluten cultivars JN17were higherthan that of TN18during the whole grain filling stages. The present result indicated thatshading during grain filling had no effect on the origination formation time of HMW-GS, butincreased the HMW-GS content and decreased the HMW-GS amount per grain in wheat grainat maturity.The HMW-GS content was negatively correlated with the volume proportion of granules<10and <100m and positively correlated with the volume proportions of GMPgranules>100m, while the total HMW-GS content was not significantly correlated with theproportion by volume of GMP granules10-100m, which indicated that the correlationbetween larger GMP granules and HMW-GS content may account for a positive relationshipbetween GMP and HMW-GS. The present result showed that an increase in the totalHMW-GS content enhanced the volume proportion of larger GMP granules induced byshading.2The study of wheat growth and development mechanism at different shading intens-itiesLow-intensity shading increased grain yield by9.9%and6.6%in Jinan17and Tainong18respectively, while the grain yield was reduced significantly by mid and serious shading afteranthesis in both Jinan17(multiple-spikes cultivar) and Tainong18(Larger-spikes cultivar) inthe present study. There had compensation effect on grain yield under shading, and the compensation effect decreased with the increasing shading intensity. In addition, thecompensation was higher in the multiple-spikes cultivar (Jinan17) than the larger-spikescultivar (Tainong18) under low shading. The different shading intensities treatmentssignificantly decreased the maximum grain filling rates and postponed the time of themaximum grain filling rates. The grain filling duration times in JN17were increased byshading after anthesis, while it was decreased by shading after anthesis in TN18.The different shading intensities treatments especially serious shading treatment alldecreased the dry matter accumulation after anthesis, the two cultivars showed the sametrends. The mid and serious shading increased the redistribution of stored dry matter fromvegetative organs into grains, while low shading increased the contribution of dry matteraccumulated from anthesis to maturity to the grain. In addition, under all shading treatments,the multiple-spike cultivar Jinan17could remobilize more dry matter stored in vegetativeorgans into grains than the larger-spike cultivar Tainong18to compensate the loss ofphotosynthesis after anthesis ascribed to shading.In the present study, we found that serious shading decreased photosynthesis of top threeleaves during the whole grain filling stages for both cultivars, while under low shading,photosynthesis of the top three leaves in both cultivars all increased during the whole grainfilling stages compared with control. In addition, mid shading reduced Pn of flag leaf andincreased Pn of penultimate and third leaves in both cultivars. Shading reduced the leaf areaindex at the early grain filling stages, however, LAI was increased at the late grain fillingstages for both cultivars by shading. In addition, serious shading brought forward theformation of the maximum LAI for the both cultivars. Low shading increased the fraction ofbottom leaf area in Jinan17and the fraction of top leaf area in Tainong18respectively, whilemid and serious shading all increased the fraction of top leaf area in both cultivars. However,better light transmission was found in the whole canopy in Jinan17and bottom layer of wheatcanopy in Tainong18under shading than the control. The PS system centre was found not tobe essentially damaged by shading, and inversely low shading increased Fv/Fm, PS andETR, and decreased NPQ in the top three leaves. However serious shading damaged PS system activity of top three leaves including decreasing Fv/Fo, PS and ETR, andincreasing the light energy which was dispersed via heat. This indicated that low shadingincreased the light absorption and use efficiency, and then increased the photosynthesis.The different shading intensities treatments decreased the free amino acid content andglutamate synthetase activity of top three leaves in JN17during the early grain filling stages, however increased them at late grain filling stages. This indicated that shading after anthesissignificantly decreased the protein degradation and postponed senescence of top three leavesduring the early grain filling stages. While during the late grain filling stages, shading afteranthesis increased remobilization of accumulated protein in leaves and it's contribution tograin.3The study of effect of nitrogen application times on wheat growth and developmentmechanism under shadingThe increased ratio of nitrogen application at late grain filling could significantlyincrease the kernels per spike and grain yield, while had no effect on spikes per area. Thisindicated that increasing ratio of nitrogen application at late grain filling, especially at headingstages could increase the grain yield from augmenting the kernels per spike to alleviate theharmful effect of shading on wheat grain yield.Under shading, the increased ratio of nitrogen application at late grain filling couldsignificantly increase the photosynthesis of top three leaves in JN17, especially at thepenultimate and third leaves. Increasing ratio of nitrogen application at late grain fillingsignificantly increase the Fv/F0, ETR and PS, while had no effect on Fv/Fm. NPQ was alsodecreased by increasing ratio of nitrogen application at late grain filling stages. This indicatedthat increasing ratio of nitrogen application at late grain filling stages increased the lightabsorption and use efficiency, and then increased the photosynthesis.Increasing the ratio of nitrogen application at late grain filling stages decreased thedegradative enzymet and glutamate synthetase activity of top three leaves in JN17during theearly grain filling stages, however increased them at late grain filling stages. Free amino acidcontent of top three leaves showed increasing trend with increasing the ratio of nitrogenapplication at late grain filling stages. This indicated that increasing the ratio of nitrogenapplication at late grain filling stages significantly decreased the protein degradation andpostponed senescence of top three leaves during the early grain filling stages. While duringthe late grain filling stages, increasing the ratio of nitrogen application at late grain fillingstages under shading increased remobilization of accumulated protein in leaves and it'scontribution to grain.