水稻胚乳组织的结构观察

【目的】阐明水稻糊粉层细胞、亚糊粉层细胞与中心胚乳贮藏细胞的结构特性。【方法】采用光镜、透射电镜与扫描电镜对水稻胚乳组织进行观察研究。【结果】糊粉层细胞分化过程中,大液泡变成小体积蛋白贮存液泡,蛋白贮存液泡又转变成糊粉粒。颖果背部比腹部有更多层糊粉层,但背部糊粉层细胞内糊粉粒的形成与积累速度却较慢。亚糊粉层细胞起初含有一些脂质体,后来脂质体消失,而其内部淀粉体与蛋白体逐渐增多。中心胚乳贮藏细胞含有淀粉体与蛋白体,蛋白体以液泡型蛋白体为主,它们可以相互融合而变大。中心胚乳贮藏细胞内的淀粉积累速度明显快于亚糊粉层细胞内的。成熟颖果的中心胚乳贮藏细胞内淀粉体最为密集,背部和侧部的亚糊粉层细胞内淀粉体排列较疏松,腹部的亚糊粉层细胞内淀粉体最为稀疏。【结论】水稻颖果背部与腹部的糊粉层细胞和亚糊粉层细胞的结构差异可能与养分吸收与转运有关;中心胚乳贮藏细胞内淀粉体发育速度快于亚糊粉层细胞。     

Water penetration into rice grains during soaking observed by gradient echo magnetic resonance imaging

The water penetration into a rice grain during soaking was monitored by three-dimensional gradient echo magnetic resonance imaging, which has the advantage of a short measurement time and a sufficient sensitivity for low-moisture samples. The water penetration route was compared between the milled and brown rice grains of two japonica cultivars. In normal milled rice grains of Koshihikari, water first penetrated the ventral side surface and the embryo attachment site of the endosperm, then migrated along the central line and transverse cracks, and finally diffused to all parts of the endosperm. In milled rice grains of Yamadanishiki with a white core, water quickly infiltrated into the cracks or chalky parts on the dorsiventral line and then diffused to the lateral side. In brown rice grains of both cultivars water penetrated extremely slowly and did not infiltrate directly into transverse cracks or the white core due to inhibition by the pericarp and seed coat. The central part of every grain allowed more water to penetrate. The route, pattern and speed of water penetration were determined by the morphological structure, crack formation and hardness distribution associated with the packing of the starch granules in the grain.     

Water penetration into rice grains during soaking observed by gradient echo magnetic resonance imaging

The water penetration into a rice grain during soaking was monitored by three-dimensional gradient echo magnetic resonance imaging, which has the advantage of a short measurement time and a sufficient sensitivity for low-moisture samples. The water penetration route was compared between the milled and brown rice grains of two japonica cultivars. In normal milled rice grains of Koshihikari, water first penetrated the ventral side surface and the embryo attachment site of the endosperm, then migrated along the central line and transverse cracks, and finally diffused to all parts of the endosperm. In milled rice grains of Yamadanishiki with a white core, water quickly infiltrated into the cracks or chalky parts on the dorsiventral line and then diffused to the lateral side. In brown rice grains of both cultivars water penetrated extremely slowly and did not infiltrate directly into transverse cracks or the white core due to inhibition by the pericarp and seed coat. The central part of every grain allowed more water to penetrate. The route, pattern and speed of water penetration were determined by the morphological structure, crack formation and hardness distribution associated with the packing of the starch granules in the grain.     

Effect of High Temperature at Ripening Stage on the Reserve Accumulation in Seed in Some Rice Cultivars

Abstract

The resistance to high-temperature stress and the structural appearance of the imperfect grains caused by a high temperature at the ripening stage were studied using 13 selected cultivars of rice. High temperature treatment (daily maximum temperature range, 32-40°C) given from the 4th day after heading caused the decrease in panicle weight in all of the cultivars examined. The number of empty grains in the upper and lower parts of a panicle was increased by the high temperature in 10 cultivars. Cultivars KRN, Citanduy, Belle patna and BPB were tolerant to the high-temperature treatment at the ripening stage, and cvs. Koshihikari, Sanlicun, Tainung 67, Yamada-nishiki and Lady Wright were sensitive. Light microscopic observation showed that, the whole endosperm was covered with a nucellar epidermis (NE) under both high and natural temperature (26-31°C) conditions at the first week after heading (WAH). Under high-temperature conditions the NE degenerated earlier than under natural temperature conditions. Scanning electron microscopic observation showed that, the endosperm cells of the seeds with a specific gravity (s.g.) of higher than 1.06 had large amyloplasts filled with starch granules. However, the endosperm cells of seeds with a s.g. of 1.00-1.06 had many small amyloplasts containing small single starch granules and had numerous spaces among the amyloplasts. In the endosperm cells at the dorsal side of imperfect grain, layered structures showing progressive decomposition of starch granules were observed.     

施氮时期对扬稻6号颖果发育及稻米品质的影响

通过盆栽试验研究了相同施氮量下不同施氮时期（分蘖期和孕穗期）对扬稻6号颖果发育及稻米品质的影响。与对照相比,增施氮肥（尿素）特别是孕穗肥能显著提高稻米精米率、整精米率、蛋白质含量,降低垩白粒率和直链淀粉含量;在分蘖期和孕穗期施氮肥能明显影响颖果发育,提高粒重,而后者的效果更为明显;在颖果发育过程中不同时期增施氮肥能显著降低颖果的总淀粉和直链淀粉含量,但对支链淀粉含量影响较小;不同时期增施氮肥特别是孕穗肥对淀粉体和蛋白质体的发育及结构均有显著影响,能显著改变籽粒中不同部位特别是腹部淀粉体和蛋白质的分布、数目和形状。与对照相比,淀粉体和蛋白质体的排列更紧密、相互间空隙较少、数量增加、密度增大,淀粉体形状多数呈晶状体。     

Effects of Nitrogen Application Time on Caryopsis Development and Grain Quality of Rice Variety Yangdao 6

A pot experiment was conducted to study the effects of different nitrogen application time(during the tillering or the booting stages)with the same nitrogen rates on the caryopsis development and grain quality of rice variety Yangdao 6.The increased nitrogen fertilizer(urea),especially applied during the booting stage,could evidently increase the milled rice rate,head rice rate and protein content in rice grains compared with the control(no nitrogen application),and decrease chalky grain rate and amylose content.Moreover,the increased nitrogen fertilizer significantly affected the caryopsis development and enhanced the grain weight when nitrogen applied during the tillering and the booting stages,especially during the booting stage.During caryopsis development the increased nitrogen fertilizer applied during the tillering and booting stages could obviously decrease the total starch and amylose contents,but not obviously for the amylopectin content in rice grain.Increased topdressing of nitrogen fertilizer,especially applied during the booting stage,had significant effect on the development and structures of amyloplasts and proteinoplasts.That is,it could change the distribution,number and shape of amyloplasts and proteinoplasts in the endosperm cells especially in grain abdomen.Compared with the control the arrangements of amyloplasts and proteinoplasts were closer,with more numbers,higher density and less interspaces each ohter.Furthermore,most amyloplasts showed polyhedron under the increased nitrogen fertilizer level.     

早籼稻垩白形成中胚乳淀粉粒发育的电镜观察

对不同垩白度早籼品种中优早3号（少垩白）和泸红早1号（多垩白）的不同温度处理下的胚乳淀粉粒进行了扫描电镜观察,结果显示胚乳腹部淀粉粒形成的发育过程明显受温度条件的影响。在灌浆初始,高温促使淀粉粒发育进程提前,淀粉粒形状呈圆球形,边缘光滑,从而造成成熟时淀粉粒间的空隙明显,结构疏松,垩白率高。这在少垩白品种中优早3号中表现得尤为显著。     

Differences of Physicochemical Properties Between Chalky and Translucent Parts of Rice Grains

Rice grain chalkiness is an important characteristic, but the difference between chalky and translucent parts in grains is still unclear. Here, we investigated the differences of flour made from the chalky or translucent part of rice grains in three indica and three japonica rice varieties. The chalky flour had significantly lower amylose and protein contents and looser starch granule morphology, and starches in the chalky flour had higher relative crystallinity, higher short chain content but lower long chain content than those in the translucent flour. The water states, determined with nuclear magnetic resonance, differed between the chalky and translucent flour after soaking, cooking and retrograding, and the chalky flour had more bound and free water but less constructural water than the translucent flour. Mostly, the chalky flour had lower viscosity and shorter gel consistency, but higher onset temperature and gelatinization enthalpy than the translucent flour. The results indicated that starch granule morphology would be more indicative than other attributions on pasting and gelatinization properties of chalky and translucent parts of rice grains.     

小麦内胚乳细胞及其淀粉体的发育

为了探明小麦内胚乳细胞发育和淀粉体生长的规律,以不同发育天数的小麦颖果为材料,利用树脂半薄切片和胚乳细胞分离等方法研究了内胚乳细胞及其淀粉体的形态、数目和生长过程.结果如下:(1)小麦内胚乳细胞呈不规则的多面体形态,内含大、小两种淀粉体,大淀粉体呈鹅卵石形,小淀粉体呈圆球形;(2)内胚乳细胞的生长呈“S”型曲线,花后16～24 d是细胞生长最快的时期;(3)大淀粉体的增殖和生长主要在花后4～16 d进行,小淀粉体在花后16 d大量出现并快速增殖,至胚乳发育后期小淀粉体数量占内胚乳细胞淀粉体总量的90％以上;(4)内胚乳细胞核在颖果发育中、后期发生衰亡,淀粉体在核衰亡过程中仍然能增殖和生长.     

两个玉米品种胚乳发育的比较

以农乐988和扬糯1号两个品种的玉米颖果为材料,利用树脂半薄切片、组织化学染色及生理测定等方法研究胚乳组织和细胞的发育过程。结果表明,两个玉米品种粒重及淀粉含量的变化呈S形生长曲线;可溶性糖变化呈单峰曲线,授粉后12 d含量最高;总蛋白含量在授粉后6 d较高。颖果粒重和总蛋白含量农乐988>扬糯1号;可溶性糖及淀粉含量扬糯1号>农乐988。授粉后0~2 d胚乳处在游离核期,授粉后3~5 d胚乳处在细胞化期,授粉6 d以后胚乳细胞开始分化,内胚乳细胞出现淀粉体和蛋白体。胚乳中淀粉的积累由颖果顶端向基部、由胚乳外层向中央推进。扬糯1号胚乳发育较提前,失活较晚;农乐988胚乳发育相对滞后,失活较早。玉米胚乳发育和颖果发育关系紧密,胚乳游离核期和细胞化期相当于颖果形成期,胚乳分化期相当于颖果乳熟期,胚乳成熟期相当于颖果蜡熟期与完熟期。     

α-Amylase Activity and Soluble Sugar Supply from Endosperm in Relation to Varietal Differences in Seedling Establishment under Low-Temperature Conditions in Rice (Oryza sativa L.)

Abstract

We examined 𰂱-amylase(EC 3.2.1.1) activity in endosperm in 6 varieties of rice (Oryza sativa L.), which showed different seedling establishment traits in field experiments, using seedlings grown in sterilized agar-bed at 16ºC. At the coleoptile elongation stage and the first leaf elongation stage, there were significant differences in 𰂱-amylase activity among the varieties investigated. However, the varietal difference in 𰂱-amylase activity at the coleoptile elongation stage did not correspond with that in coleoptile growth. Maltose, the immediate product of 𰂱 -amylase activity, accumulated in the endosperm at the coleoptile elongation stage in a greater amount in Fukuhibiki, which has a poor seedling establishment trait, than in Arroz da Terra, which has a superior seedling establishment trait. The concentration of glucose detected in the exudate from the endosperm adjacent to the scutellum at the coleoptile elongation stage was also higher in Fukuhibiki than in Arroz da Terra. The results obtained in sterileagar-bed conditions clearly demonstrated that neither deficiency in 𰂱-amylase activity nor glucose production in the endosperm were responsible for coleoptile growth retardation at 16ºC. Therefore, neither 𰂱-amylase activity nor sugar supply from the endosperm were responsible for the varietal differences seen in the rate of seedling establishment in paddy fields at around 16ºC.     

外源水杨酸对高温胁迫下小麦籽粒灌浆特性的影响

为探究外源水杨酸(SA)对高温胁迫下小麦产量形成特性的影响,以扬麦18为试验材料,于2018-2020年进行盆栽试验,分别在小麦抽穗期(SAHG)、开花期(SAAG)、花后5 d(SA5G)以及花后10 d(SA10G)对其喷施水杨酸(SA),在灌浆期(花后15～19 d)采用被动式模拟增温方法对其进行高温胁迫,分析不同处理对小麦产量及其相关指标的影响。结果表明,与常温对照(NN)相比,灌浆期高温胁迫(NG)显著降低了小麦的产量和千粒重,不同时期喷施SA显著降低了高温胁迫下产量和千粒重的下降幅度,不同处理缓解效果表现为SAAG>SA5G>SA10G>SAHG。外源SA处理缓解了高温胁迫对小麦不同穗位强、弱势粒粒重的损害,对上部小穗及弱势粒粒重的影响较为显著,从而缓解了高温胁迫下小麦产量的降低。喷施SA显著降低了灌浆期高温胁迫下籽粒蔗糖含量、可溶性糖含量、蔗糖合成酶(SS)活性的降低幅度,提高了籽粒中吲哚乙酸(IAA)、脱落酸(ABA)、细胞分裂素(CTK)的含量。推测喷施SA通过调控小麦籽粒内源激素水平提高籽粒糖类物质含量,进而缓解高温胁迫对产量影响。     

不同籼稻颖果发育及其结构与品质性状

比较了两个籼稻品种颖果的发育,籽粒的主要品质性状以及胚乳淀粉体的大小、形状、结构等特性。结果表明： 扬稻6号的主要品质性状优于湘早籼33;在开花后前期扬稻6号干物质积累速率较慢,但在后期较快,淀粉充实度较高; 淀粉胚乳细胞内存在两种淀粉体,即单粒淀粉体,直径2.4~8.0 μm,平均4.7 μm;复合淀粉体,即由多个单粒淀粉体结合而成,直径5.7~19.5 μm,平均9.7 μm。湘早籼33单粒淀粉体多数为椭圆形或圆球形,大小差异较大,排列疏松,变异系数较大;扬稻6号胚乳单粒淀粉体基本为晶体多面形,发育良好,大小较为一致,排列紧密,变异系数较小。胚乳背部淀粉体的发育和排列结构优于腹部和中部。胚乳垩白的出现是由于淀粉体发育不良、排列疏松所致,而淀粉体的充实又与灌浆物质的输入途径紧密相关。     

High temperature and low solar radiation during ripening differentially affect the composition of milky-white grains in rice (Oryza sativa L.)

ABSTRACT

Temperatures and solar radiation during ripening critically affect grain appearance in rice (Oryza sativa L.). Climatic factors to induce chalky grains were analyzed under the experimental conditions of high-temperature and shading treatment and also under the ambient condition in a high-temperature-prone region of Japan. The frequency of white-back (WB) and basal-white (BW) grains correlated with temperature and solar radiation, whereas that of milky-white (MW) grains was not correlated, suggesting that complicated climatic factors are involved in the formation of MW grains. Further investigation was carried out to identify the parameters that distinguish perfect and MW grains grown in high-temperature versus those grown in low-solar-radiation conditions. As reported previously, the chalk phenotypes in the transverse section of the MW grains were quite different between environments: oval-shaped chalk for MW grains grown in low-solar-radiation condition and center chalk for MW grains grown in high-temperature condition. Grain hardness and amylopectin chain-length distribution did not explain the difference in MW grains between environments. MW grains subjected to high temperatures had a lower protein content without a consistent reduction in the single-grain weight, whereas those from the low-solar-radiation condition had a lower amylose content with a consistent reduction in the single-grain weight, when compared with perfect grains that developed in either environmental condition. Overall, our results suggest that MW grains are formed through different physiological mechanisms with altered starch and protein synthesis under high-temperature and low-solar-radiation conditions.

Abbreviations: BW: basal-white; DAH: days after heading; DP: degree of polymerization; MW; milky-white WB: white-back     

Relationships among the chalkiness,kernel size and endosperm cell morphology of rice kernels at different spikelet positions within a panicle

The occurrence of chalky kernels in rice is causally related to kernel size and endosperm morphology. This study aimed to investigate the occurrence of chalky kernels by analyzing kernel size, and the number and area of endosperm cells. Spikelets were sampled from upper and middle primary branches and lower secondary branches in a panicle, and divided into four categories: upper, middle, and lower perfect (PF) kernels and lower milky-white (MW) kernels. On the lower secondary branches, there was a higher percentage of chalky kernels, with smaller kernel lengths, widths and thicknesses, than the kernels on the upper and middle primary branches. MW kernels were smaller in size than PF kernels even on the same lower secondary branches. Regardless of grain appearance quality traits, the total areas of endosperm cross sections in lower kernels were significantly smaller than in upper kernels owing to the decreased cell area, and there was a significant negative correlation between the number of cells and average cell area. When the numbers and the areas of cells were analyzed using angular 30° intervals from the line connecting the center point and the dorsal vascular bundle, the MW kernels had significantly less cells than PF kernels near the ventral side at 120–180°. Thus, the decrease in the number of cells near the ventral side was a main causal factor in the decrease in MW kernel widths compared with PF kernel widths, and this suggested that cell division in MW kernels was inhibited at the early grain-filling stage.     

Effect of high temperature stress during ripening on the accumulation of key storage compounds among Japanese highly palatable rice cultivars

High temperature stress during ripening increases the frequency of chalky grains, resulting in a lower market value for rice (Oryza sativa L.). Changes in starch properties and the accumulation pattern of storage proteins are proposed to be related to the occurrence of chalky grains. This study investigated changes in the accumulation of key storage compounds in the grains of Japanese highly palatable rice cultivars, subjected to high temperature stress when grown in a growth chamber and the field. The 13 kDa prolamin content was significantly reduced in a highly heat-sensitive cultivar, Tsukushiroman, whereas the 13 kDa prolamin content was not affected in a heat-tolerant cultivar, Genkitsukushi, even in a high temperature chamber condition (31/26 °C day/night), when compared with the control chamber condition (26/21 °C day/night) for both genotypes. In addition, grains grown in field conditions revealed that severely chalky grains had less 13 kDa prolamin than perfect grains in all five genotypes. Changes in amylose content and the distribution of amylopectin chain lengths did not explain the difference in grain appearance both for chamber and field experiments. These results strongly suggest that physiological processes linked with the synthesis of 13 kDa prolamin are associated with grain appearance in Japanese highly palatable under high temperature stress.     

Relationships of Ethylene Evolution Rate and 1-Aminocylopropane-1-Carboxylic Acid Concentration in Grains during Filling Period with Appearance Quality of Rice

To elucidate the relationship between ethylene evolution from the grains and the appearance quality of rice,ten different rice genotypes were used to determine the ethylene evolution rate,1-aminocylopropane-1-carboxylic acid(ACC)concentration in grains during grain filling and the appearance quality of rice,and the effects of chemical regulators on concentrations of ethylene and ACC in the grains during grain filling were also investigated to verify the roles of ethylene in the rice quality formation.The ethylene evolution rates and ACC concentrations in grains during the mid and late grain filling stages were very significantly and positively correlated with chalky kernel percentage and chalkiness.The cultivars with a low ACC concentration in grains exhibited a close amyloplast arrangement and small space between starch granules,whereas those with a high ACC concentration in grains showed a loose arrangement and wide space between the granules.Application of 1μmol/L ACC to panicles at mid and late grain filling stages significantly loosened amyloplast arrangement and increased chalky kernel percentage,chalky area and chalkiness,and the results were reversed when 1μmol/L amino-ethoxyvinylglycine,an inhibitor of ACC synthesis enzyme,was applied to panicles.A practice of moderate dry-wet alternate irrigation reduced ethylene evolution and ACC concentration in grains and thereby reduced chalkiness. The results suggested that ethylene and ACC in grains play an important role in the endosperm structure and appearance quality of rice,and the appearance quality would be improved by reducing ethylene evolution and ACC in grains through either variety breeding and selection,or chemical regulations or cultivation techniques.     

Effects of Popping on the Endosperm Cell Walls of Sorghum and Maize

The structure of the vitreous endosperm of raw and popped grains of popcorn maize and sorghum has been examined by light and scanning electron microscopy. In both cereals, popping produces everted grains consisting of expanded endosperm foam attached to the pericarp and embryo tissue. As previously reported, each bubble of the foam is formed from an individual starch granule inflated by internal steam pressure. Large fissures may contribute significantly to the expansion of the endosperm foam. The cell walls of the vitreous endosperm of both cereals are shattered into small fragments, which separate slightly as the cell contents expand during popping. Despite this, the endosperm cells retain their polygonal outline. Intact cell walls of raw endosperm, wall fragments from popped endosperm foam, and fragments isolated after treatment of the foam withalpha -amylase, were visualised through the autofluorescence of their ferulic acid content. The in vitro digestibility of popped sorghum was unchanged compared to raw sorghum, whereas that of wet-cooked sorghum was greatly reduced. It is suggested that popping-induced wall fragmentation improves the accessibility of the protein and starch reserves of the endosperm to digestive enzymes.     

Enhanced Nitrogen Uptake and Photosynthesis of Rice Grown with Deep and Permanent Irrigation Method: Possible Mechanism for Chalky Grain Reduction

Abstract

Recently, the occurrence of chalky grain caused by high temperature stress at the ripening stage has been a global problem for rice. We previously showed that the deep and permanent irrigation method, which is the combination of the V-furrow direct seeding and deep-flood irrigation methods, reduced chalky grain occurrence. To study the possible physiological mechanisms for reduced chalky grain occurrence by the deep and permanent irrigation method, we conducted field experiments in 2008 and 2009 to examine the effects of the deep-flood treatment on plant nitrogen (N) content, stomatal conductance and photosynthetic rate especially at the ripening stage. Results showed that in the deep-flood treatment that maintained a 20 cm water depth, leaf N content was consistently and significantly higher than the control with only a 10 cm water depth. Except two measured days, the stomatal conductance under the deep-flood treatment was significantly higher than in the control. Furthermore, stomatal conductance and photosynthetic rate in the deep-flood treatment were always significantly higher than in the control in both years. Thus, the deep-flood treatment enhanced N uptake, and consequently photosynthetic activity, resulting in the reduction of chalky grain formation, as previously reported. Accordingly, the effects of deep- flood treatment on grain quality improvement in rice may possibly be attributed to the improvement in source activity.