Relationship between structural and biochemical characteristics and texture of corn grains

The texture of corn grains is a fundamental characteristic for the industry as well as for grain producers and processors. To further understand the mechanisms involved in grain hardness, contrasting corn cultivars for grain hardness and protein quality were evaluated. The cultivars were Cateto L237/67 (hard endosperm and low protein value), QPM BR 451 (semi-hard endosperm and high protein value); Bolivia-2 (floury endosperm and low protein value), and Opaque-2 (floury endosperm and high protein value). Evaluations were carried out at 10, 20, 30, 40, 50, and 60 days after pollination in developing corn grains and in the mature grain. In developing grains, evaluation consisted in the determination of the area, percentage of starch granules, distribution of starch granules, and protein bodies in the endosperm. In mature corn grains, the parameters evaluated were: density, percentage of total proteins, levels of lysine and tryptophan, and banding pattern of zeins. The results indicate that the higher physical resistance of corn grains from the cultivars analyzed is influenced by the high percentage of total proteins, high synthesis of 27-kDa zeins, presence of protein bodies, and perfect organization of starch granules in the endosperm, independent of their sizes.     

Short-term effects of experimental warming and enhanced ultraviolet-B radiation on photosynthesis and antioxidant defense of <Emphasis Type="Italic">Picea asperata</Emphasis> seedlings

It is generally accepted that sucrose synthase (SuSy), ADP-glucose pyrophosphorylase (AGPase), soluble starch synthase (SSS), granule-bound starch synthases (GBSS) and starch branching enzyme (SBE) play a key role in starch synthesis in wheat grains. Starch synthesis in wheat grains is influenced by genotype and environment. However, what is not known is the degree of variation in enzyme activity during starch accumulation of wheat cultivars differing in kernel types. The present study was carried out to characterize the changing activities of key enzymes during grain filling in two kernel type winter wheat cultivars. Results showed that starch accumulation rate (SAR) and activities of SuSy, AGPase, SSS, GBSS and SBE in large kernel types were significantly higher than those in small kernel types. The soil water deficit experienced during the course of the experiment led to an increase at early grain-filling period and decrease during late grain-filling, respectively, in SAR and activities of key enzymes involved in starch synthesis, especially SuSy, AGPase, SSS, and SBE. Water deficit enhanced grain starch accumulation in small kernel types. It suggests that rainfed treatment increase physiological activities during early grain-filling and promote starch accumulation in small kernel types. The simulation with Richards’ equation showed that it was accumulation duration and SAR that determined the starch accumulation in large kernel types. Compared with small kernel types, plants of large kernel types maintained longer filling duration, higher SAR and greater activities of related enzymes during mid and late grain-filling. These observations suggest stronger sink activities in large kernel types at a later stage of development. Consequently, large kernel types have advantages over the small kernel types in terms of the amount of starch accumulation at mid and late stage, but are sensitive to water deficit.     

不同供水条件对小麦强、弱势籽粒中淀粉粒度分布的影响

以3个淀粉含量不同的冬小麦品种山农12、鲁麦21和济南17为材料,设灌溉和旱作2种栽培处理,对不同水分条件下小麦强、弱势籽粒中淀粉粒的体积、数目和表面积的分布特征进行了研究.结果表明,小麦强、弱势籽粒均含有A(＞9.8 μm)、B(2.0～9.8 μm)、C(＜2.0 μm)3种类型的淀粉粒,但不同类型淀粉粒的分布状况存在明显差异.在强势籽粒中,淀粉粒的体积和表面积分布均表现为三峰分布,而弱势籽粒中淀粉粒的体积和表面积分布则表现为双峰分布.与弱势粒相比较,强势粒中C型淀粉粒(＜2.0 μm)的体积百分比为7.25%～9.31%,表面积百分比为34.88%～41.51%,而弱势粒的体积和表面积百分比分别为5.33%～6.40%和26.31%～33.54%.强、弱势籽粒中＜0.6 μm和0.6～2.0 μm范围内的淀粉粒数目存在明显差异,强势粒为1.86%～6.13%和83.77%～87.77%,而弱势粒为25.72%～37.42%和52.77%～58.48%.与灌溉栽培相比较,旱作栽培条件下籽粒中B、C型淀粉粒体积和表面积百分比显著增加,而A型淀粉粒体积和表面积显著减少;弱势粒中＜0.6 μm的淀粉粒数目显著增加,强势籽粒中淀粉粒的数目无显著变化.与弱势粒相比较,强势粒中的蛋白质含量较高,C型淀粉粒的体积和表面积所占比例较大,而强势粒中的淀粉含量较低,且A、B型淀粉粒比例也较小.与灌溉栽培相比较,旱作栽培条件下强、弱势籽粒中B、C型淀粉粒体积和表面积百分比增加,蛋白质含量也显著增加,淀粉含量降低.表明水分亏缺能提高籽粒中B、C型淀粉粒体积和表面积百分比及蛋白质含量.     

Genetic diversity and phylogeny of Japanese sake-brewing rice as revealed by AFLP and nuclear and chloroplast SSR markers

Japanese rice (Oryza sativa L.) cultivars that are strictly used for the brewing of sake (Japanese rice wine) represent a unique and traditional group. These cultivars are characterized by common traits such as large grain size with low protein content and a large, central white-core structure. To understand the genetic diversity and phylogenetic characteristics of sake-brewing rice, we performed amplified fragment length polymorphism and simple sequence repeat analyses, using 95 cultivars of local and modern sake-brewing rice together with 76 cultivars of local and modern cooking rice. Our analysis of both nuclear and chloroplast genome polymorphisms showed that the genetic diversity in sake-brewing rice cultivars was much smaller than the diversity found in cooking rice cultivars. Interestingly, the genetic diversity within the modern sake-brewing cultivars was about twofold higher than the diversity within the local sake-brewing cultivars, which was in contrast to the cooking cultivars. This is most likely due to introgression of the modern cooking cultivars into the modern sake-brewing cultivars through breeding practices. Cluster analysis and chloroplast haplotype analysis suggested that the local sake-brewing cultivars originated monophyletically in the western regions of Japan. Analysis of variance tests showed that several markers were significantly associated with sake-brewing traits, particularly with the large white-core structure.     

Post-anthesis alternate wetting and moderate soil drying enhances activities of key enzymes in sucrose-to-starch conversion in inferior spikelets of rice

This study tested the hypothesis that a post-anthesis moderate soil drying can improve grain filling through regulating the key enzymes in the sucrose-to-starch pathway in the grains of rice (Oryza sativa L.). Two rice cultivars were field grown and two irrigation regimes, alternate wetting and moderate soil drying (WMD) and conventional irrigation (CI, continuously flooded), were imposed during the grain-filling period. The grain-filling rate and activities of four key enzymes in sucrose-to-starch conversion, sucrose synthase (SuSase), adenosine diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE), showed no significant difference between WMD and CI regimes for the earlier flowering superior spikelets. However, they were significantly enhanced by the WMD for the later flowering inferior spikelets. The activities of both soluble and insoluble acid invertase in the grains were little affected by the WMD. The two cultivars showed the same tendencies. The activities of SuSase, AGPase, StSase, and SBE in grains were very significantly correlated with the grain-filling rate. The abscisic acid (ABA) concentration in inferior spikelets was remarkably increased in the WMD and very significantly correlated with activities of SuSase, AGPase, StSase, and SBE. Application of ABA on plants under CI produced similar results to those seen in plants receiving WMD. Applying fluridone, an indirect inhibitor of ABA synthesis, produced the opposite effect. The results suggest that post-anthesis WMD could enhance sink strength by regulating the key enzymes involved, and consequently, increase the grain-filling rate and grain weight of inferior spikelets. ABA plays an important role in this process.     

Scanning Electron Microscope Observation on Endosperm Starch Grain Cnaracters in Orvza sativa subsp. Hsien

Scanning electron microscope observation on the characters of endosperm starch grains of wild rice anti seventeen hsien rice varieties belonging to first and second season cropping indicated that endosperm starch grains of hsien rice generally were polyhedron in sharp and edgy angle indistinct of polyhedron, individual starch grain nearly subrounded in the parts called white belly and white centre. General diameters are in an extent of 3.3–9.3 mm. The shapes of the endosperm starch grains between wild rice and cultivars are similar and sizes leas than hsien rice varieties, but the sizes of the endosperm starch grains of the first eropp4ng axe large than those of the second cropping. The shapes of endosperm starch grains of the varieties to have good exterior quality are polyhedron and structures are arranged closely, Hance, it can be primarily distinguished the good quality of grains from the poor by observation on the endosperm starch grains of varieties.     

Enzymatic Improvement of the Cooking Quality of Aged Rice: A Main Mode of Protease Action

This study aims to improve the stickiness and brightness of cooked rice from aged rice grains by removing its albumins and globulins with proteases. In newly–harvested grains, the proteins were easily removed by extraction with water which contained minerals from rice. In aged grains, however, the proteins were already denatured and extracted with difficulty. Proteases hydrolyzed even the denatured proteins to make them extractable. As a result, starch granules on the surface of grains were liberated. Some proteases also hydrolyzed a starch granule-associated protein, and consequently, made the starch highly gelatinizable by heating. The protease treatment of aged grains was effective for two main reasons: liberation of starch granules and removal of the granule-associated protein. During cooking of rice the liberated starch without the associated proteins gelatinized to give rise to stickiness. The gelatinized starch is considered to form a more isotropic film on the surface of every cooked rice grain to give brightness as well.     

Genetic dissection of grain traits in Yamadanishiki,an excellent sake-brewing rice cultivar

Key message

The grain traits of Yamadanishiki, an excellent sake-brewing rice cultivar in Japan, are governed by multiple QTLs, namely, a total of 42 QTLs including six major QTLs.

Abstract

Japanese rice wine (sake) is produced using brewing rice (Oryza sativa L.) that carries traits desirable for sake-brewing, such as a larger grain size and higher white-core expression rate (WCE) compared to cooking rice cultivars. However, the genetic basis for these traits in brewing rice cultivars is still unclear. We performed analyses of quantitative trait locus (QTL) of grain and days to heading over 3 years on populations derived from crosses between Koshihikari, a cooking rice, and Yamadanishiki, an excellent sake-brewing rice. A total of 42 QTLs were detected for the grain traits, and the Yamadanishiki alleles at 16 QTLs contributed to larger grain size. Two major QTLs essential for regulating both 100-grain weight (GWt) and grain width (GWh) were harbored in the same regions on chromosomes 5 and 10. An interaction was noted between the environment and the QTL associated with WCE on chromosome 6, which was detected in two of 3 years. In addition, two QTLs for WCE on chromosomes 3 and 10 overlapped with the QTLs for GWt and GWh, suggesting that QTLs associated with grain size also play an important role in the formation of white-core. Despite differences in the rate of grain growth in both Koshihikari and Yamadanishiki across 2 years, the WCE in Yamadanishiki remained consistent, thus demonstrating that the formation of white-core does not depend on grain filling speed. These data can be informative for programs involved in breeding better cooking and brewing rice cultivars.

     

Waterlogging and simulated acid rain after anthesis deteriorate starch quality in wheat grain

The synthesis and accumulation of starch is greatly affected by environmental stress. Wheat grown in the downstream area of the Yangtze River is easily subjected to stress of waterlogging and acid rain. In order to probe the effect of waterlogging and acid rain on yield and starch characteristic, we used winter wheat cultivars of Yangmai 16 (more resistant) and Wennong 17 (relatively sensitive) to sole stress of acid rain or waterlogging and to their combinations during grain filling. The responses of grain yield, the physiochemical properties and morphology of starch granules in endosperm to the stresses were investigated. Compared with CT (control), grain yield in Wennong 17 were significantly decreased by both pH 4.0 acid rain and pH 2.5 acid rain, while in Yangmai 16 only by pH 2.5 acid rain. Waterlogging combined with acid rain significantly reduced grain weight and grain yield in both wheat cultivars. Acid rain, waterlogging and their combination depressed activities of ADP glucose pyrophosphorylase and soluble starch synthase (SSS) in grains of both cultivars. Acid rain and waterlogging damaged endosperm cell structure and caused abnormal starch granules. Starch granules at maturity became fragile and failed to keep in shape and some granules were even totally submerged in the protein matrix and other tissue under acid rain and waterlogging. Content of amylopectin and amylopectin/amylose ratio was also decreased, while content of amylose was increased under acid rain and waterlogging. As a result, swelling power and most viscosity parameters decreased, while the pasting temperature increased in both cultivars due to stresses. In sum, acid rain and waterlogging and their combination damaged cell structure and depressed synthesis of amylopectin, and led to the formation of abnormal fragile starch granules, and finally reduced grain weight and then yield, and deteriorated starch quality.     

Gene expression of the biosynthetic enzymes and biosynthesis of starch during Rice Grain development

Amylose and amylopectin are determinants of the physicochemical properties for starch and grain quality in rice. Their biosynthesis is catalyzed by the interplay of ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS), a starch branching enzyme (SBE), and a starch debranching enzyme (SDE). In this study, the genes for these enzymes were highly expressed 7 to 28 days after flowering during grain development, and their expression closely matched increases in both starch content and grain weight Among all the tested cultivars, amylose contents in the rice grains remained essentially constant throughout their development The AGPase gene was highly expressed in the high-yield cultivars of both glutinous and non-glutinous rice. The SSS gene was actively expressed when mature GBSS mRNA decreased. Genes responsible for amylopectin biosynthesis were simultaneously expressed in the late stage of grain development. We have now demonstrated that the expression patterns of starch biosynthetic genes differ between glutinous and non-glutinous rice, and between Tongil (a Japonica/ Indica hybrid) and Japonica types.     

Amylose Content and Starch Granule Size in Rice Grains are Affected By Growing Season

Amylose content and starch granule size in grains influence rice quality, which differs between the early (ES) and late season (LS). The objective of this study was to determine the variation of amylose content and starch granule size between seasons and find the main reasons (e.g., temperature and solar radiation) for the observed variation. Field experiments with six rice varieties (three high and three low amylose content rice) planted in the ES and LS were conducted in 2016 and 2017, respectively. The mean temperatures during the filling stage were higher in ES, however, the daily temperatures at 7-10 days after flowering (DAF) in 2016, and at 5-10, 13-14 DAF in 2017 were higher in LS. The results showed that amylose content in LS was lower than in ES with high amylose content rice varieties (HACV); the opposite trend occurred with low amylose content rice varieties (LACV). The mean starch granule diameter was higher in LS than ES in 2016, but the opposite result occurred in 2017 with all rice. Our results suggest that higher temperatures increased and decreased the amylose content in HACV and LACV, respectively. Temperatures at 5-15 DAF were important for the formation of starch granules: lower temperatures during 10-14 DAF increased the proportion of larger starch granules (d＞6.21 μm, some with d＞13.3 μm), and higher temperatures at 5-6 DAF increased the proportion of starch granules with diameter 4.24-6.21 μm.     

Amylose Content,Morphology, Crystal Structure,and Thermal Properties of Starch Grains in Main and Ratoon Rice Crops

Rice ratooning, or the production of a second rice crop from stubble after the harvest of the main crop, is considered to be a green and resource-efficient rice production system. The present study was conducted to examine variance in amylose content (AC), grain morphology, crystal structure, and thermal properties of starch between main- and ratoon-season rice of seven varieties. Ratoon-season rice grains had higher ACs and significantly lower transition gelatinization temperatures (To, Tp, and Tc) than did main-season rice grains. The relative crystallinity and lamellar peak intensity of ratoon-season rice starch were 7.89% and 20.38% lower, respectively, than those of main-season rice starch. In addition, smaller granules with smoother surfaces and lower thermal parameters were observed in the starch of ratoon-season rice. The relative crystallinity and lamellar peak intensity of starch correlated negatively with the AC and positively with transition gelatinization temperatures. These results suggest that the superior cooking quality of ratoon-season rice is attributable to the moderate increase of grain AC, which reduces the relative crystallinity, weakens the crystal structure, and lead to a decrease in the gelatinization temperature.     

水氮互作对小麦籽粒蛋白质、淀粉含量及其组分的影响

以两个不同品质类型的小麦品种（强筋品种豫麦34、弱筋品种豫麦50）为材料,在大田条件下,研究了3个灌水处理（W₁：拔节水;W₂：拔节水+花后15 d灌浆水;W₃：拔节水+灌浆水+花后28 d麦黄水）和3个氮肥水平（0、150、270 kg·hm^-2）对籽粒蛋白质、淀粉含量及其组分的影响.结果表明：270 kg·hm^-2的施氮量有利于提高强筋小麦（豫麦34）籽粒蛋白质含量,籽粒清蛋白、醇溶蛋白和谷蛋白含量明显提高,谷/醇增大;支链淀粉和总淀粉含量提高,直/支下降;籽粒产量增加.弱筋小麦（豫麦50）在150 kg·hm^-2 的施氮量下,清蛋白和醇溶蛋白含量增加,球蛋白和谷蛋白含量下降,谷/醇降低;支链淀粉和总淀粉含量提高;不施氮肥或氮肥施用过多（270 kg·hm^-2）均影响籽粒蛋白质和淀粉的积累,使产量下降.W₂处理促进了籽粒蛋白质和淀粉积累,W₁或W₃处理均不利于籽粒蛋白质和淀粉积累,且导致籽粒产量下降.水、氮互作效应中,强筋和弱筋小麦分别以全生育期270 kg·hm^-2和150 kg·hm^-2施氮量配合拔节水+灌浆水（W₂）为比较理想的水氮运筹方式.     

OsPKpα1 encodes a plastidic pyruvate kinase that affects starch biosynthesis in the rice endosperm

Pyruvate kinase (PK) is a key enzyme in glycolysis and carbon metabolism. Here, we isolated a rice (Oryza sativa) mutant, w59, with a white-core floury endosperm. Map-based cloning of w59 identified a mutation in OsPKpα1, which encodes a plastidic isoform of PK (PKp). OsPKpα1 localizes to the amyloplast stroma in the developing endosperm, and the mutation of OsPKpα1 in w59 decreases the plastidic PK activity, resulting in dramatic changes to the lipid biosynthesis in seeds. The w59 grains were also characterized by a marked decrease in starch content. Consistent with a decrease in number and size of the w59 amyloplasts, large empty spaces were observed in the central region of the w59 endosperm, at the early grain-filling stage. Moreover, a phylogenetic analysis revealed four potential rice isoforms of OsPKp. We validated the in vitro PK activity of these OsPKps through reconstituting active PKp complexes derived from inactive individual OsPKps, revealing the heteromeric structure of rice PKps, which was further confirmed using a protein-protein interaction analysis. These findings suggest a functional connection between lipid and starch synthesis in rice endosperm amyloplasts.     

Effects of the activities of key enzymes involved in starch biosynthesis on the fine structure of amylopectin in developing rice (Oryza sativa L.) endosperms

The dynamic changes of the activities of enzymes involving in starch biosynthesis, including ADP-glucose pyrophosphorylase (AGPase), soluble starch synthases (SSS), starch branching enzyme (SBE) and starch debranching enzymes (DBE) were studied, and changes of fine structure of amy- lopectin were characterized by isoamylase treatment during rice grain development, using trans anti-waxy gene rice plants. The relationships between the activities of those key enzymes were also analyzed. The amylose synthesis was significantly inhibited in transgenic Wanjing 9522, but the total starch content and final grain weight were less affected as compared with those of non-transgenic Wanjing 9522 rice cultivar. Analyses on the changes of activities of enzymes involving in starch bio- synthesis showed that different enzyme activities were expressed differently during rice endosperm development. Soluble starch synthase is relatively highly expressed in earlier stage of endosperm de- velopment, whilst maximal expression of granule-bound starch synthase (GBSS) occurred in mid-stage of endosperm development. No obvious differences in changes of the activities of AGPase and SBE between two rice cultivars investigated, except the DBEs. Distribution patterns of branches of amy- lopectin changed continually during the development of rice grains and varied between two rice culti- vars. It was suggested that amylopectin synthesis be prior to the synthesis of amylose and different enzymes have different roles in controlling syntheses of branches of amylopectin.     

Endosperm enzyme activity is responsible for texture and eating quality of cooked rice grains in Japanese cultivars

Eating quality of cooked rice grains is an important determinant of its market price and consumer acceptance. To comprehensively assess the variation of eating-quality traits in 152 Japanese rice cultivars, we evaluated activities of eight endosperm enzymes related to degradation of starch and cell-wall polysaccharides. Endosperm enzyme activities showed a wide range of variations and were lower in recently developed cultivars than in landraces and old improved cultivars. Activities of most endosperm enzymes correlated significantly with the eating-quality score and surface texture of cooked rice grains. Principal component analysis revealed that rice cultivars with high eating-quality scores had high stickiness of the grain surface and low levels of endosperm enzyme activities. These results suggest that endosperm enzyme activities control texture and eating quality of cooked rice grains in Japanese rice cultivars.     

Nature of Lysolecithin in Rice Grains

Problems of the interaction between starch and lysolecithin are treated in this article. The endosperm of rice grains was fractionated and it was found that lysolecithin was associated with starch granules. The association was not a mere adsorption, but rather a more firm combination. It was demonstrated that lysolecithin had an ability to combine with starch in aqueous solution, and to cause amylose to precipitate, but not amylopectin. The lysolecithin-amylose complex was isolated, and it was shown that lysolecithin is most certainly included in the helicoidal structure of amylose chain. A possible role of lysolecithin during the course of the starch formation in rice grains is discussed.     

Carbohydrate metabolism enzymes in CO2-enriched developing rice grains of cultivars varying in grain size

The increased supply of photosynthate from maternal tissue is known to promote grain growth in several crop species. However, the effect of increasing photosynthate supply on grain growth receives little attention in rice. This study was aimed at evaluating the effect of increasing photosynthate supply through CO₂ enrichment (650 μl I_-1) on grain growth in three rice cultivars differing in grain size. CO₂ enrichment was applied to the pot-grown plants between anthesis and final harvest. The results indicated that high CO₂ treatment enhanced the CO₂ exchange rate of leaf tissue, and subsequently increased the sucrose level of peduncle exudate, but it did not promote starch accumulation in the developing grains. This phenomenon was linked to the poor CO₂ responses for the grain activities of sucrose synthase, UDP-glucose pyrophosphorylase. ADP-glucose pyrophosphorylase, and starch synthases involved in the conversion of sucrose to starch. Significant cultivar differences also existed for the activities of sucrose to starch conversion enzymes with larger grain size cultivars tending to have higher enzymes activities (expressed on a grain basis), resulting in a greater carbohydrate accumulation.     

PEARL MILLET (PENNISETUM AMERICANUM (L.) LEEKE) AND GRAIN SORGHUM (SORGHUM BICOLOR (L.) MOENCH) ULTRASTRUCTURE

Ultrastructural features of pearl millet (Pennisetum americanum (L.) Leeke) and grain sorghum (Sorghum bicolor (L.) Moench) caryospses were investigated with thin sections of the dry, mature grain in the transmission electron microscope, and fractured kernels in the scanning electron microscope. The pericarp of those grains is comprised of three distinct layers: epicarp, mesocarp of parenchyma cells, and endocarp of compressed cross and tube cells. Mesocarp cells of grain sorghum contain starch granules embedded in a cytoplasmic matrix. The major constituent of sorghum and millet aleurone cells are aleurone grains (protein bodies) and lipid bodies. Subaleurone cells contain a much higher proportion of protein bodies than starch granules, and the protein bodies are structurally distinct from those in the aleurone. The germ scutellar ultrastructures of the two grains were similar; protein bodies, lipid bodies, epidermal cells and parenchyma cells of the germ are described.