Environmental factors associated with glutenin polymer assembly during grain maturation

This study aims to understand the environmental factors, focusing on rain and fungal infection, affecting the assembly of glutenin polymers during grain maturation. Spring wheat was grown in the field and grains were sampled from 50% grain moisture until maturity. Grain moisture content, protein content, size of glutenin polymers, the presence of proteases, and the amount of DNA from common wheat pathogenic fungi were analysed.Rain influenced the rate of grain desiccation that occurred parallel to the rate of glutenin polymer assembly. Rapid desiccation contributed to faster glutenin polymer assembly than gradual desiccation. Severe reduction in the glutenin polymer size coincided with increased grain moisture due to rain. Furthermore, increased fungal DNA followed by presence of gluten-degrading proteases was observed in the grain after humid conditions. The presence of gluten-degrading proteases was presumably involved in reducing the size of glutenin polymers in grain.Our study gave new insight into how environmental conditions could be associated with the assembly of glutenin polymers during grain maturation. The results suggest that rain and/or fungal proteases play an important role in reducing the molecular size of glutenin polymers.     

Polymerisation of gluten proteins in developing wheat grain as affected by desiccation

The breadmaking quality of wheat is affected by the composition of gluten proteins and the polymerisation of subunits that are synthesised and accumulated in developing wheat grain. The biological mechanisms and time course of these events during grain development are documented, but not widely confirmed. Therefore, the aim of this study was to monitor the accumulation of gluten protein subunits and the size distribution of protein aggregates during grain development. The effect of desiccation on the polymerisation of gluten proteins and the functional properties of gluten were also studied. The results showed that the size of glutenin polymers remained consistently low until yellow ripeness (YR), while it increased during grain desiccation after YR. Hence, this polymerisation process was presumed to be initiated by desiccation. A similar polymerisation event was also observed when premature grains were dried artificially. The composition of gluten proteins, the ratios of glutenin to gliadin and high molecular weight-glutenin subunits to low molecular weight-glutenin subunits, in premature grain after artificial desiccation showed close association with the size of glutenin polymers in artificially dried grain. Functional properties of gluten in these samples were also associated with polymer size after artificial desiccation.     

Water stress during grain development affects starch synthesis,composition and physicochemical properties in triticale

Triticale, a man-made cereal crop developed from a cross between wheat and rye, has excellent agronomic traits to produce starch for bioindustrial applications. The effects of different levels of water stress on expression of starch synthesis genes and starch composition and physicochemical properties were investigated in this study. Three triticale varieties from 5 days post-anthesis were treated with three levels of water stress: low water stress (LWS) at 55–60% of soil moisture, moderate water stress (MWS) at 30–35% soil moisture and severe water stress (SWS) at 10–15% soil moisture. Water stress led to a significant reduction in seed weight at SWS (35–45%). A decrease in starch content was noticeable from MWS onwards and the values were decreased by 42–55% at SWS across all varieties. Such decrease was associated with the reduced expression of starch synthesis genes at 19 days of water stress (DWS). MWS favoured an increase of amylose proportion in triticale starch and it was accompanied by a significant up-regulation of GBSSI expression throughout the grain development. Triticale starch synthesized under water stress showed a reduced population of small granules and an increase of A-type to B-type ratio. SWS caused pitting on starch granules but did not alter the biconcave disc shape of mature granules. An inverse relationship between water stress and a range of starch gelatinization temperature was observed and the MWS environment specifically decreased the peak temperature (Tp) and increased the enthalpy. Our results signify that starch morphology, composition and physicochemical properties in triticale grains could be altered if triticale is grown under drought conditions.     

Zinc nutrition influences the protein composition of flour in bread wheat (Triticum aestivum L.)

Zinc (Zn) deficiency and heat stress during grain filling occur in a number of important wheat growing regions around the world. The changes in grain protein composition due to high temperature are well documented, but little is known about the effect of grain Zn and its interaction with heat stress. Six field experiments were conducted at sites differing in grain filling temperatures to examine these effects. Two varieties of bread wheat were grown at six rates of Zn, including foliar sprays of Zn. The relative amounts of gliadin and polymeric protein were measured by size exclusion HPLC. Applying Zn increased grain yield at three sites and altered protein quality at two of these. Foliar Zn applications doubled grain Zn concentration, reduced the proportion of gliadin and SDS-unextractable polymeric protein and increased the proportion of SDS-extractable polymeric protein. Heat stress during grain filling was associated with a high proportion of gliadin and low proportions of the polymeric protein in the grain. However, the proportions of gliadin and of SDS-extractable polymeric protein were less affected by high temperatures in grain with high Zn concentrations. The results demonstrate that Zn nutrition can alter protein composition and the effects of Zn may interact with grain filling temperatures.     

灌浆期不同时段高温对稻米淀粉理化特性的影响

【目的】研究灌浆期不同时段高温对稻米淀粉组成、结构和理化特性的影响,揭示高温对稻米淀粉理化特性影响的时段效应,阐明高温、结构和功能之间的关系。【方法】以耐热水稻品种黄华占和热敏感的9311近等位基因系为实验材料,利用人工气候箱设置高温[38℃(昼)/30℃(夜)]和对照[28℃(昼)/22℃(夜)],研究灌浆前期(齐穗期后1－15 d)和后期(齐穗期后16 d至成熟)高温对稻米的加工品质、外观品质、淀粉组成、支链淀粉链长分布、粒度分布、胶稠度、黏度特性、糊化特性、结晶特性和颗粒形态的影响。【结果】灌浆期高温使糙米率、精米率、整精米率显著下降,使垩白粒率和垩白度显著升高,导致加工品质和外观品质变差。灌浆期高温使总淀粉含量、直链淀粉含量、短支链淀粉含量、大淀粉粒占比、直/支链淀粉比显著下降,而中等支链淀粉含量、小中淀粉粒占比、糊化温度和糊化焓显著上升,黏度特性显著改变,结晶类型不变但结晶度显著改变,淀粉颗粒表面出现小孔,表面变得凹凸不平,导致淀粉颗粒更加碎片化和蒸煮食味品质变劣。灌浆期不同时段高温对稻米品质的影响不同,灌浆前期高温对稻米淀粉的影响大于灌浆后期,耐热品种受影响小于热敏感品种。灌浆前期高温处理下供试材料具有较高的消减值和较低的崩解值,黏度特性变差;灌浆后期高温处理下供试材料具有较低的消减值和较高的崩解值,黏度特性变好。【结论】灌浆前期高温对淀粉理化特性的影响最大,进而导致稻米的加工品质、外观品质和蒸煮食味品质变劣,灌浆后期高温提升了黏度特性。     

Water stress during grain development affects starch synthesis,composition and physicochemical properties in triticale

Triticale, a man-made cereal crop developed from a cross between wheat and rye, has excellent agronomic traits to produce starch for bioindustrial applications. The effects of different levels of water stress on expression of starch synthesis genes and starch composition and physicochemical properties were investigated in this study. Three triticale varieties from 5 days post-anthesis were treated with three levels of water stress: low water stress (LWS) at 55–60% of soil moisture, moderate water stress (MWS) at 30–35% soil moisture and severe water stress (SWS) at 10–15% soil moisture. Water stress led to a significant reduction in seed weight at SWS (35–45%). A decrease in starch content was noticeable from MWS onwards and the values were decreased by 42–55% at SWS across all varieties. Such decrease was associated with the reduced expression of starch synthesis genes at 19 days of water stress (DWS). MWS favoured an increase of amylose proportion in triticale starch and it was accompanied by a significant up-regulation of GBSSI expression throughout the grain development. Triticale starch synthesized under water stress showed a reduced population of small granules and an increase of A-type to B-type ratio. SWS caused pitting on starch granules but did not alter the biconcave disc shape of mature granules. An inverse relationship between water stress and a range of starch gelatinization temperature was observed and the MWS environment specifically decreased the peak temperature (Tp) and increased the enthalpy. Our results signify that starch morphology, composition and physicochemical properties in triticale grains could be altered if triticale is grown under drought conditions.     

灌浆期遮阴对小麦胚乳淀粉粒度分布及糊化特性的影响

为了解灌浆期遮阴对小麦胚乳淀粉粒度分布及淀粉糊化特性的影响,研究了灌浆期对扬麦13、宁麦13和烟农19进行30%遮阴后籽粒的淀粉粒度分布与糊化特性的变化。结果表明,小麦灌浆期遮阴显著降低了<10μm的B型淀粉粒体积和表面积占比,增加了>10μm的A型淀粉粒的体积和表面积占比,其中A型淀粉粒中主要增加了10~20μm淀粉粒的体积和表面积占比;遮阴处理对淀粉粒数目分布无显著影响。遮阴处理后,峰值粘度、低谷粘度、稀懈值、最终粘度、回升值等糊化参数指标均显著降低。小麦籽粒硬度、容重、出粉率等指标也因遮阴处理而显著降低。综上所述,遮阴处理改变了小麦籽粒淀粉粒粒度分布,降低了淀粉糊化参数和加工品质。     

Combined effect of genetic and environmental factors on the accumulation of proteins in the wheat grain and their relationship to bread-making quality

Bread-making quality of wheat flour is largely determined by the accumulation, concentration and composition of the proteins in the grain, which are influenced by genetic (G) and environment (E) variation and their interactions. We have therefore evaluated the importance of G and E factors and their interactions in determining the accumulation and composition of the proteins in the wheat grain. The cultivar determined development time (CDDT), together with the amount and timing of N application, played a significant role in determining the accumulation and final composition of the wheat grain proteins, explaining 21–59% of the variation. At low temperature, N application both at spike formation and at anthesis explained the highest proportion of variation (36%) in the percentage of sodium dodecyl sulphate (SDS) unextractable polymers in the total amount of polymers (% UPP), while at high temperature CDDT contributed most to the variation in % UPP (20%). The largest contributor to variation in the amount of total SDS extractable proteins (TOTE) was N application at anthesis, both at low and high temperatures (12% and 36%, respectively). Thus, the climate should be considered in recommendations for improving the protein quality and thereby the bread-making quality of wheat.     

Responses of glutamine synthetase activity and gene expression to nitrogen levels in winter wheat cultivars with different grain protein content

Glutamine synthetase (GS) plays a central role in plant nitrogen (N) metabolism, which improves crops grain protein content. A pot experiment in field condition was carried out to evaluate GS expression and activity, and grain protein content in high (Wanmai16) and low grain protein (Loumai24) wheat cultivars under two N levels (0.05 and 0.15 g N kg⁻¹ soil). High nitrogen (HN) resulted in significant increases in GS1 and GS2 expression at 10 days after anthesis (DAA), and higher GS activity during the entire grain filling stage. HN also significantly increased yield, grain protein content and protein fraction (except for glutenin of Luomai24) in two wheat cultivars, which indicated that it increased grain yield and protein content by improving nitrogen metabolism. Wanmai16 showed higher grain protein content, gliadin and glutenin content, and had higher expression level of GS2 both in flag leaves and grains at early grain filling stage. However, Luomai24 had greater yield and higher expression level of GS1. The difference expression of GS2 and GS1 genes indicates they had various contributions to the accumulation of protein and starch in wheat grains, respectively. The results suggest that GS2 would be serving as a potential breeding target for improving wheat quality.     

Sulfhydryl-disulfide changes in storage proteins of developing wheat grain: influence on the SDS-unextractable glutenin polymer formation

To understand more precisely the function of free glutenin SH and SS groups in glutenins of developing wheat for UPP formation, a specific sulfhydryl probe, monobromobimane (mBBr), was used for an in vitro protein labeling. By applying this procedure to two varieties of wheat differing in high molecular weight glutenin subunit composition (2*, 7+8, 5+10 and 0, 6+8, 2+12, respectively, for Soissons and Thésée), we showed that the major wheat glutenin subunits residing in the protein body undergo redox change during the development and the maturation of the grain. Indeed, during the cell division and the cell enlargement phase, glutenin subunits and particularly LMW-GS have a large amount of free SH groups and become oxidized during grain dehydration which coincided with the formation of UPP. Moreover, mBBr derivatization of free glutenin SH groups before the artificial grain desiccation inhibits the UPP deposition. As HPSEC-MALLS analysis showed, the alkylation of free glutenin SH groups before the desiccation induces an increase in the SDS solubility of the polymeric proteins by reducing both their molecular weight distribution and their compactness. These results are discussed in connection with an ‘hyperaggregation model’ which has been proposed to explain the formation of glutenin polymer in wheat kernel.     

灌浆期高温对冬小麦叶源与粒库生理特征的影响

为研究灌浆期高温对冬小麦灌浆和产量的影响,以耐热型品种淮麦33和高温敏感型品种华成3366为材料,于灌浆期(花后14～20 d)进行高温处理,以田间自然温度生长的小麦为对照,研究高温对旗叶叶绿素含量、抗氧化酶活性、丙二醛(MDA)含量和糖含量以及籽粒淀粉含量和淀粉合成关键酶活性的影响,并对小麦粒重、产量等指标进行测定。结果表明,高温处理显著降低了淮麦33和华成3366旗叶的叶绿素含量,降幅分别为5.88%和9.86%;降低了两品种旗叶的抗氧化酶活性,提高了旗叶MDA、可溶性糖和蔗糖含量;高温处理也显著降低了两品种籽粒的腺苷二磷酸葡萄糖焦磷酸化酶(AGPase)、结合态淀粉合成酶(GBSS)、可溶性淀粉合成酶(SSS)和淀粉分支酶(SBE)活性,并减少了支链淀粉和总淀粉含量,其中淮麦33和华成3366的籽粒总淀粉含量分别下降了5.63%和8.77%;高温处理主要降低了淮麦33小穗第3粒位的粒重及华成3366小穗第1、2和3粒位的粒重,2018-2019、2019-2020年度淮麦33和华成3366的产量分别下降了5.07%和16.33%、6.23%和8.90%。与高温敏感型品种华成336...     

Starch granules size distribution in superior and inferior grains of wheat is related to enzyme activities and their gene expressions during grain filling

Mature wheat endosperm contains A-, B-, C-type starch granules, and each class has unique physiochemical properties which determine the quality of starch. The dynamics of the starch granule size distribution, activities of starch synthases and expression of starch synthase encoding genes were studied in superior and inferior grains during grain filling. Compared with inferior grains, superior grains showed higher grain weight, contents of starch, amylose and amylopectin. The formation of A-, B-, C-type starch granules initiated at 4, 8, 20 DAF, respectively, and was well consistent with the temporally change patterns of starch synthase activities and relative gene expression levels. For instance, activities of soluble and granule-bound starch synthases (designated SSS and GBSS) peaked at 20 and 24 DAF. Genes encoding isoforms of starch synthases expressed at different grain filling periods. In addition, SS I was generally expressed over the grain filling stage; the SS II and SS III were expressed over the early and mid grain filling stage, and the GBSS I was expressed during the mid to late grain filling stage. In addition, the time-course changes in activities of starch synthases and expression of starch synthase encoding genes explained well the dynamics of the starch granule size distribution.     

Characterization of physicochemical qualities and starch structures of two indica rice varieties tolerant to high temperature during grain filling

An extreme high temperature during grain filling is an important environmental factor that reduce the yield and quality of rice. In this study, we compared the grain appearance, composition and starch structure of four rice varieties response to high temperature during grain filling. The results obviously revealed that two indica AUS varieties Halwa and Jamir showed more tolerance to high temperature during grain filling than either the japonica Nipponbare or another AUS rice DJ24. The data showed that Halwa and Jamir presented less chalkiness, less grain weight loss, less change of endosperm components as well as starch structure than Nipponbare and DJ24 under high temperature treatment. Hence, the results implied that Halwa and Jamir might be useful targets to further identify genetic mechanism response to high temperature, at least during grain filling and endosperm development. Moreover, these AUS varieties have potential application value in further breeding of rice with good quality and heat tolerance.     

不同品质类型小麦籽粒游离氨基酸、蛋白质及其组分的动态变化

为了解小麦氮素营养代谢的动态变化规律,给优质专用小麦品种选育与应用提供科学依据,选用不同品质类型的四个小麦品种(系)济南17、PH82-2-2、PH97-4、PH97-5,在两种施氮水平和两种追肥时期下研究了籽粒游离氨基酸、蛋白质及其组分的动态变化.结果表明,籽粒发育初期游离氨基酸含量高,随籽粒发育其含量逐渐下降;蛋白质含量积累呈现"高-低-高"的变化趋势,品种之间差异显著,成熟期蛋白质含量高的品种一般有较高的游离氨基酸和蛋白质积累水平.不同品质类型小麦籽粒蛋白质组分含量变化动态基本一致,灌浆初期清蛋白含量较高,随籽粒发育逐渐下降,灌浆中后期下降趋缓;球蛋白总体含量水平较低,随籽粒发育缓慢下降,灌浆末期略有上升.醇溶蛋白在籽粒发育前期积累较少,花后14 d快速积累;谷蛋白在花后7 d已有一定的积累,随后其含量逐渐上升,强筋高蛋白品种有较高的醇溶蛋白和谷蛋白积累水平,在成熟籽粒蛋白质中谷蛋白和醇溶蛋白所占比例也高,弱筋低蛋白品种有相对较低的醇溶蛋白和谷蛋白积累,醇溶蛋白和谷蛋白所占比例也低.     

藁城8901与豫麦50籽粒淀粉粒的粒度分布特征

为研究小麦籽粒发育过程中胚乳淀粉粒形成与粒度分布特征,以小麦品种藁城8901与豫麦50为材料,研究了籽粒胚乳淀粉粒形成、生长与分布特征。结果表明,花后4d,小麦胚乳出现不同范围大小的淀粉粒,最大粒径8μm。花后7d,籽粒中淀粉粒增多增大,最大粒径20μm左右。花后10~14d,淀粉粒体积继续增大,并产生了一个新的小淀粉粒群体。花后17d,淀粉粒以体积增大为主。花后21d,淀粉粒最大粒径较成熟期变化较小。花后24d,小于0.6μm的淀粉粒数目急剧增加,大于0.6μm的淀粉粒数目占比则明显减少,表明这一时期又产生了一个新淀粉粒群体(后期形成的B型淀粉粒)。花后24~28d,小于0.6μm的淀粉粒数目仍不断增加,而直径较大的淀粉粒数目增加减少,表明籽粒中新淀粉粒的产生仍在继续,但以小粒径淀粉粒为主。花后28d至成熟期,最小粒径淀粉粒进一步生长,其他淀粉粒粒径变化相对较小。     

Starch granule morphology in oat endosperm

Mature and developing oat (Avena sativa) grains were sectioned and image analysis methods used to estimate the starch granule-size distribution and morphology in endosperm cells. This showed that oat endosperm cells contain two types of starch granule: compound starch granules such as those seen in rice endosperm and in most other grasses; and simple granules similar to the B-type starch granules seen in the endosperm of Triticeae species such as wheat (Triticum aestivum). The simple granules in oats are similar in size and relative abundance to B-type granules in Triticeae suggesting that they may share a common evolutionary origin. However, there is a fundamental difference between oats and Triticeae in the timing of granule initiation during grain development. In Triticeae, the B-type granules initiate several days after the A-type granules whereas in oats, both the simple and compound granule types initiate at the same time, in early grain development.     

不同温光型专用小麦品种花后旗叶生理与籽粒淀粉积累特性

为探索不同温光型专用小麦籽粒淀粉的积累规律及其与植株生长状况的关系,在大田条件下,以2类温光型和3种筋型的小麦品种为材料,研究花后旗叶的生理特性和籽粒淀粉及组分积累情况。结果表明,旗叶中叶绿素含量在灌浆前期(0~21d)维持较高,后期迅速下降,但2个弱筋型品种下降速度缓慢;半冬性品种旗叶中可溶性蛋白含量均大于弱春性品种,而丙二醛(MDA)含量小于弱春性品种,差异均达极显著水平(P0.01)。不同筋型籽粒淀粉组分和总淀粉的积累动态以弱筋型品种最具优势,其直链淀粉含量均在花后14d进入快速增长期,支链淀粉和总淀粉含量在花后28d仍在持续增加,最终以半冬性弱筋品种的籽粒产量和淀粉产量最高(P0.01)。灌浆前期(0~21d),叶绿素、可溶性蛋白含量与直链淀粉、支链淀粉和总淀粉含量呈显著和极显著的相关性(P0.01,P0.05);灌浆后期(21~28d),与直链淀粉的相关性不显著,而叶绿素含量与支链淀粉含量的相关性增大。由此可见,旗叶维持较高的叶绿素、可溶性蛋白含量,较低的丙二醛含量在灌浆前期有利于直链淀粉的积累,后期有利于支链淀粉的积累。     

Partitioning and conversion of 14C-photoassimilates in developing grains of wheat plants grown under field conditions in Cuba

Understanding the patterns of source–sink relationships in wheat under field conditions is crucial to determine the physiological factors limiting grain filling. The aim of this investigation was to assess the time-course of source–sink interactions in wheat after anthesis under Cuban field conditions. For this purpose, plants of wheat, cultivar Cuba C-204, were sown in the field at six dates with contrasting temperature conditions. The duration of grain filling, patterns of partitioning of ¹⁴C-photoassimilates between organs and incorporation of the label into starch in the kernels 24 h after feeding the flag leaf blade with ¹⁴CO₂, were investigated to evaluate source–sink balance. The proportion of ¹⁴C converted into starch in the kernels increased during the first 10 days of grain filling. Throughout the grain filling phase the proportion of total ¹⁴C fixed partitioned to the grains increased, whereas that allocated to the internodes decreased. At the beginning of grain filling, the patterns of ¹⁴C-photoassimilate partitioning differed among sowing dates. Additionally, the proportion of ¹⁴C incorporated into starch in the kernels correlated positively with the proportion of the label partitioned to the grains, but negatively with ¹⁴C accumulation in the internodes. This supports that the accumulation of ¹⁴C in the stem was closely related to the uptake capacity of the grains. The lack of such a relationship at later stages in grain development indicates a change from sink-limited to source-limited situation early after anthesis. In conclusion, the supply of photoassimilates under field conditions in Cuba limits grain filling, except the first days after anthesis, when it was sink-limited.