| With the increasing economic development and the continuous improvement of people’s living standards,the quality of wheat grains is receiving widespread attention.How to improve the quality of wheat on the basis of increasing wheat yield has become one of the main goals of wheat production.Wheat grain quality is not only determined by cultivar characteristics,but also affected by environmental factors,among which temperature and water are the key climate factors that affect wheat grain quality.Under the background of global warming,the frequency of high temperature and drought stress in the later wheat growth period was projected to gradually increase,posing serious threat for wheat grain yield and quality.Therefore,it is of great significance to determine the interactive effects of high temperature and drought stress on wheat grain nutritional quality.In this study,YM 23 and XM 33 were used as research materials,and the artificial climate chamber was used to implement high temperature and drought stress experiments that conformed to the diurnal variation of temperature,to clarify the interactive effects of different levels of high temperature and drought stress during anthesis and grain filling stages on the spatial distribution of protein and starch,17 kinds of amino acid quality and 5kinds of mineral elements in mature wheat grains.The main results are as follows:(1)The protein content of wheat grains in the cultivars increased first and then decreased as a single-peak curve from the outside layer to the inside layer,and the protein content in P2 and P3 layers was the highest,while the protein content in P8 and P9 layers was the lowest.The starch content in different layers of wheat grain in the two cultivars increased gradually from P1 to P6 or P7,and decreased slowly from layer P7 to P9 as a single-peak curve.The starch content in layer P6-P7 was the highest,while the starch content in layer P1 was the lowest.With the increase of high temperature level and drought stress level,the protein content in different levels of grain showed an increasing trend,while the starch content showed a decreasing trend.Under high temperature and drought stress,the increase of grain protein content was generally as follows: the endosperm layer(P4-P9)> aleurone layer(P2-P3 layer)and > seed layer(P1 layer),while the decrease of starch content was generally as follows: the seed layer(P1 layer)> aleurone layer(P2-P3layer)and > endosperm layer(P4-P9 layer).High temperature and drought stress show significant interactive effects on the content of protein and starch in all layers of two cultivars.The relative protein content in all layers generally increased with the increase of high temperature degree-day(HDD),while the relative starch content decreased with the increase of HDD.The sensitivity of relative protein content to HDD in the two cultivars were higher for stress at grain filling stage than at anthesis,while the sensitivity of relative starch content to HDD were higher for stress at anthesis than at grain filling stage.Content of protein and starch of different layers in YM 23 was more sensitive to high temperature and drought stress than XM 33.(2)The contents of most amino acids varied significantly between growing seasons,and growing season,treatment stage,temperature level,drought stress level and their interactions had significant effects on the contents of most amino acids.With the increase of high temperature and drought levels at anthesis and the filling stages,the contents of total amino acids,essential amino acids and non-essential amino acids in the two cultivars showed an increasing trend for most treatments,and the overall increasing range was as follows: non-essential amino acid > total amino acid > essential amino acid.For YM 23,content of phenylalanine,tyrosine and methionine was more sensitive to high temperature and drought stress at two stages than other amino acids.For XM 33,content of tyrosine and methionine was more sensitive to high temperature and drought stress at anthesis than other amino acids,while content of isoleucine and methionine was more sensitive to high temperature and drought stress at grain filling stage than other amino acids.The essential amino acid score,ratio coefficient of amino acids and essential amino acid index generally increased with the rise of high temperature and drought stress level,indicating that high temperature and drought stress to a certain extent,improved the balance of the grain amino acid composition.Among the 7 essential amino acids,lysine is always the first restrictive amino acid,while phenylalanine+tyrosine and leucine excessed in wheat grains.The relative content of amino acids in wheat grains generally increased with increasing high temperature degree-day(HDD).The sensitivity of relative amino acid content to HDD in the two cultivars were higher for stress at anthesis than at grain filling stage.The sensitivity of relative amino acid content to HDD under different drought levels in YM 23 were all higher than that of XM 33,which indicated that YM 23’s amino acid content was more sensitive to high temperature and drought stress than XM 33.(3)With the rise of high temperature and drought stress level,the content of P,K,Ca and Fe in the grains of two cultivars generally increased,but content of Zn decreased.The interactive effects of high temperature and drought stress were significant on the content of all mineral elements(except for K)in different grains of YM 23,but only significant on the content of Fe for XM 33.The accumulation of P,K and Ca in the grain of two cultivars increased under the interaction of mild high temperature and drought stress,but decreased under the interaction of severe high temperature and drought stress.The accumulation of Zn and Fe showed a decreasing trend under all stress treatments.The interactive effects of high temperature and drought stress on the accumulation of mineral elements in both cultivars were all significant.The content of most of mineral elements in wheat grains were negatively correlated with 1000-grain weight,content of starch and its components,and positively correlated with content of protein and its components,but have no significant relationship with content of dry and wet gluten.The results of quantitative analysis showed that the content of mineral elements in wheat grains increased with the rise of HDD(except for Zn),and the content of K and Fe were more sensitive to HDD than other mineral elements.Under severe drought stress,the accumulation of all mineral elements decreased with the increase of HDD,while under normal moisture and mild drought stress condition,the accumulation of all mineral elements didn’t show consistent trends with the increase of HDD.The sensitivity for content and accumulation of P and K to the interaction between high temperature and drought stress at grain filling stage was greater than that at anthesis in the two cultivars,and the sensitivity for content and accumulation of Zn and Fe to the interaction between high temperature and drought at anthesis was greater than that at grain filling stage.The sensitivity of Ca content to the interaction between high temperature and drought at the two treatment stages was similar,but the accumulation of Ca in grains was more sensitive to the interaction between high temperature and drought at anthesis than at grain filling stage.Generally,content and accumulation of mineral elements in YM 23 was more sensitive to the interaction between high temperature and drought stress than XM 33. |
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