| To understand effects of post-anthesis high temperature (HT) and drought stress(DS) on wheat grain quality and yield, the present studies, two different wheatcultivars with strong-and mid-gluten (Zhengmai366and Yunong949) used,combined pot culture with climate-controlled greenhouse simulating high temperature,were carried out to characterize effects of HT, DS and their combination on the starchgranule distribution, glutenin macropolymer particle size distribution and keyenzymes relating to N metabolism in wheat grains, and analyse the variation in starchcomponents, characteristics and protein concentration, components as well as thegrain yield. This aimed to investigate the internal mechanisms and scope that stressinfluenced on the starch and protein quality in wheat grains, and make a theoryevidence for the wheat production of high yield and high quality resisting the stress.The main results are as follows:1. The present results showed that the number distribution showed one-peakcurve, while the volume and surface area distribution all showed two-peak curve indifferent treatments. High temperature, drought stress and the combination of thesestressors during grain filling stage mainly influenced the starch volume and surfacearea distribution, but had less effect on the number distribution. High temperature,drought stress and their combination all led to a significant reduction in the volumeproportion of A-type starch granules (>9.9μm) and the surface area proportion ofgranules <2.8μm, and a significant increase in the volume proportion of granules2.8-5.8μm and5.8-9.9μm in Zhengmai366with strong-gluten. Whereas, in Yunong949with mid-gluten, HT, DS and their combination all led to a significant increase inthe volume and surface area proportion of A-type starch granules, yet a significantdecrease in the volume proportion of granules2.8-5.8μm and5.8-9.9μm. The starchgranule distribution of Zhengmai366with strong-glutenin was more sensitive tostress than Yunong949. The degree of different stress influencing the starch volume distribution showed that the combination of HT and DS at early stage of grain fillingwas greater than other stresses, following were HT applied at early stage, DS, HTapplied at mid-stage of grain filling, and the last was the combination of HT and DSat mid-stage. The starch granules were notably distorted and volume reduced by HTand DS in scanning electron microscope.2. High temperature, drought stress and its combination significantly affected thestarch concentration and its components as well as the starch characteristics in wheatgrains. The concentrations of amylose, amylopectin and total starch all decreasedunder stress treatments, yet the amylose was less sensitive to stress than amylopectinand total starch, which led to the increase in ratio of amylose to amylopectin. Thepasting characteristics of peak viscosity, hold through, final viscosity, breakdown andsetback all significantly increased in Zhengmai366and decreased in Yunong949under DS, while, that significantly declined in Zhengmai366and Yunong949underHT and the combination of HT and DS. The swelling power declined in Zhengmai366and increased in Yunong949under DS, whereas, that decreased in the two wheatcultivars under HT and the combination of HT and DS. The starch concentration andstarch characteristics in Yunong949with mid-gluten were more sensitive to stresstreatments than Zhengmai366. The HT treatments had a greater effect on the starchquality than DS, and there was a notable additive effects between HT and DS. The HTapplied at early stage of grain filling stage had greater effects than that at mid-stage.3. The correlation analysis of starch granule distribution with starchconcentration in wheat grains showed that a negative correlation existed in A-typestarch volume and surface area distribution with concentrations of total starch,amylose and amylopectin in extremely significant level, yet a positive correlationexisted in starch volume and surface area distribution in diameter of2.8-5.8μm withthat. Which indicated that starch volume and surface area distribution were moreclosely related to starch concentrations, yet starch number distribution mainly affectedamylose concentration. Starch granule distribution also had a correlation with starchcharacteristics and starch number distribution was more closely correlated with thatthan others. The correlation analysis of starch characteristics with starch concentrationshowed that swelling power, peak viscosity, final viscosity, breakdown and setbackpositively correlated with concentrations of amylopectin and total starch, and negatively correlated with ratio of amylose to amylopectin in extremely significant orsignificant level. This indicated that starch granule distribution varied with the stresstreatments and influenced concentrations of amylopectin and total starch, leading tothe variation of the ratio of amylose to amylopectin, thus affected starchcharacteristics.4. High temperature, DS and its combination all notably enhanced the totalprotein concentration. Drought stress, high temperature and their combinationtreatments at early stage of grain filling all led to a reduction in ratio of glutenin togliadin. Whereas, HT and combination of HT and DS treatments at mid-filling stagesignificantly increased the ratio of glutenin to gliadin. Protein concentration andcomponents played an important role in flour color. The value of L*was negativelycorrelated with concentrations of total protein, globulin and glutenin in extremely orsignificant level, yet positively correlated with ratio of glutenin to gliadin insignificant level. The value of a*was positively correlated with concentrations oftotal protein and glutenin in extremely significant level. The value of b*waspositively correlated with concentrations of total protein, globulin and glutenin insignificant or extremely significant level, yet negatively correlated with ratio ofglutenin to gliadin in significant level. There were differences in effects on the valueof L*, a*and b*by stress. Under stress, total protein concentration increased andprotein components changed, thus influenced the value of c and L*, a*and b*leadingto the variation of flour color.5. The activities of Glutamine synthetase (GS) and Glutamic pyruvictransaminase (GPT) of wheat grain in two wheat cultivars were all enhanced in themass by DS, HT and their combination. The correlation analysis showed that theactivities of GS and GPT in wheat grains positively correlated with gliadinconcentration and that of GPT positively correlated with total protein concentration inextremely significant level, yet GS activity in wheat grain negatively correlated withratio of glutenin to gliadin in significant level. It indicated that the activities of GS andGPT were changed by HT, DS and its combination, and then mainly influencedgliadin concentration and ratio of glutenin to gliadin, thus led to protein concentrationchanged. 6. The accumulation of glutenin macropolymer (GMP) was affected by HT, DSand its combination during grain filling stage leading to a increase of GMPconcentration at maturity in wheat grains. There were differences of GMP particledistribution by stress in different wheat cultivars. The volume and surface areaproportion of small GMP particle (<10μm) in Zhengmai366with strong-glutendeclined, while that of large particle (>100μm) increased under stress treatments.Whereas, the volume and surface area proportion of small GMP particle (<10μm) inYunong949with mid-gluten increased, still that of large particle (>100μm)decreased under stress treatments. The number distribution of GMP particle was lesssensitive to stress than others. Which indicated that the change of GMP particledistribution under stress mainly due to the variation of GMP volume and surface areaproportion, but not the change of number proportion. The correlation analysis showedthat concentrations of GMP and protein negatively correlated with the volume andsurface area proportion of GMP particle <10μm and with the surface area proportionof that <100μm in extremely significant or significant level, yet positively correlatedwith the surface area proportion of GMP particle10-100μm and>100μm. Itindicated that the concentrations of GMP and protein were influenced mainly due tothe volume and surface area proportion of GMP particle changes under stress.7. High temperature, DS and its combination all reduced the rate of grain filling,leading to the grain weight per spike, thousand grains weight and gain yield alldeclined. The duration of grain filling was shortened by6days under the combinationof HT and DS, which had greater effect on the grain yield than HT or DS. Thisindicated that there was notable superimposed effect between HT and DS. The stressalso led to a reduction in yields of protein and starch. The yield of Zhengmai366wasmore sensitive to HT, yet Yunong949was more sensitive to DS. The yields of starchand protein, main components of grain yield, played an important role in grain yield.It showed that spikes per plant, grains per spike, grain weight per spike, thousandgrains weight and grain yield per pot were all positively correlated with starchconcentration, starch yield and protein yield in extremely significant level, yetnegatively correlated with protein concentration. So it was mostly attributed to theaccumulation of starch and protein disturbed by HT, DS and its combination that thegrain yield declined. |
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