Physicochemical properties and development of wheat large and small starch granules during endosperm development

Wheat mature seeds have large, lenticular A-type starch granules, and small, spherical B-type and irregular C-type starch granules. During endosperm development, large amyloplasts came from proplastid, divided and increased in number through binary fission from 4 to 12 days after flowering (DAF). Large starch granules formed and developed in the large amyloplast. One large amyloplast had only one large starch granule. Small amyloplasts came from the protrusion of large amyloplast envelope, divided and increased in number through envelope protrusion after 12 DAF. B-type starch granules formed and developed in small amyloplast from 12 to 18 DAF, C-type starch granules formed and developed in small amyloplast after 18 DAF. Many B- and C-type starch granules might form and develop in one small amyloplast. The amyloplast envelopes were asynchronously degraded and starch granules released into cell matrix when amyloplasts were full of starch granules. Apparent amylose contents of large starch granules were higher than that of small starch granules, and increased with endosperm development. The swelling powers and crystallinity of large starch granule were lower than that of small starch granules, and decreased with endosperm development. Small starch granules displayed broader gelatinization temperature ranges than did large starch granules.     

Structure of lintnerized starch is related to X-ray diffraction pattern and susceptibility to acid and enzyme hydrolysis of starch granules

Acid-resistant residues (lintnerized starches, Ls) were prepared from starches showing A-, B- and C- X-ray diffraction patterns. Ls retained the same X-ray crystalline type as their native counterparts with an improvement in diffraction intensity. Fluorophore-assisted capillary electrophoresis (FACE) study indicated that structural characteristics of Ls were associated with X-ray diffraction patterns. Double helices originated from linear chains with an approximate average degree of polymerisation (DP) 14, 16, and 15 would span the entire length of crystalline lamellae of A-, B-, and C-type starches, respectively. The proportion of singly branched materials (SB) with DP 25 protected in Ls was higher for A-type Ls (10-17%) than for B-type Ls (4-6%) and C-type Ls (8%). The structures of SB were similar in which branched chain (DP 13-15) was longer than main chain (DP 10-12). The structural characteristics of Ls are discussed in relation to acid and enzymatic degradations of starch granules.     

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.     

The granular structure of C-type pea starch and its role in gelatinization

We have used a combination of techniques to study the structure and properties of C-type starch from pea seeds. It was found that all C-type starch granules contain both types of polymorph; the B polymorphs are in the center of the granule and are surrounded by the A polymorphs. During heating in excess salt solution the A and B polymorphs within C-type granules melt independently, giving a double transition in heat capacity and a two-step swelling, compared with single transitions for A- and B-type starches. It was shown that B polymorphs gave a transition with a lower peak temperature than A. The disruption of crystallinity during gelatinization began from the hilum area and was propagated along the granule, accompanied by swelling of disrupted areas. It is proposed that the swelling of disrupted parts of the granule decreases the melting temperature of the neighboring crystallites resulting in the progressive disruption of crystalline areas. The gelatinization process is dependent on the arrangement of A and B polymorphs within the granule. © 1998 John Wiley & Sons, Inc. Biopoly 45: 323–332, 1998     

Relationship between the distribution of the chain length of amylopectin and the crystalline structure of starch granules

The distributions of chain lengths in the amylopectins of starches from 20 species (11 A-, 6 B-, and 3 C-type) were characterised by h.p.l.c. in terms of the relationship between the molecular structure of the amylopectin and the crystalline structure of the starch granule. The weight-average chain-lengths of the amylopectins of the A-, B-, and C-type starches were in the ranges 23–29, 30–44, and 26–29, respectively. Gel-permeation chromatograms of the amylopectins debranched with isoamylase showed bimodal distributions of fractions containing long and short chains for 17 specimens (including corn, rice, potato, etc.) and trimodal distributions, of which the fraction containing short chains had twin peaks, for wheat, tapioca, and tulip amylopectins. The correlation coefficients between the average chain-lengths of amylopectins and the fractions of long and short chains and the ratio of the fractions of short and long chains by weight were 0.90, 0.69, and ?0.95, respectively. In general, amylopectin molecules of A-type starches have shorter chains in both the long- and short-chain fractions and larger amounts of the short-chain fractions than those of the B-type starches. The chain lengths of amylopectins of the C-type starches were intermediate and it is inferred that these starches possibly yield any type of crystalline structure depending on the environmental temperature and other factors, whereas the A- and B-type starches are insensitive to temperature.     

Block-Surface Staining for Differentiation of Starch and Cell Walls in Wheat Endosperm

A staining technique for differentiating starch granules and cell walls was developed for computer-assisted studies of starch granule distribution in cells of wheat [Triticum aestivum L.] caryopses. Blocks of embedded caryopses were sectioned, exposing the endosperm tissue, and stained with iodine potassium iodide (IKI) and Calcofluor White. Excessive tissue hydration during staining was avoided by using stains prepared in 80% ethanol and using short staining times. The IKI quenched background fluorescence which facilitated the use of higher concentrations of Calcofluor White. Cell wall definition was improved with the IKI-Calcofluor staining combination compared to Calcofluor alone. The high contrast between darkly stained starch granules and fluorescent cell walls permitted computer assisted analysis of data from selected hard and soft wheat varieties. The ratio of starch granule area to cell area was similar for both wheat classes. The starch granule sizes ranged from 2.1 μm³ to 22,000 μm³ with approximately 90% of the granules measuring less than 752 μm³ (ca. 11 μm in diameter). Hard wheat samples had a greater number of small starch granules and a lower mean starch granule area compared to the soft wheat varieties tested. The starch size distribution curve was bimodal for both the hard and soft wheat varieties. Three-dimensional starch size distribution was measured for four cells near the central cheek region of a single caryopsis. The percentage of small granules was higher at the ends than at the mid-section of the cells.     

Crystallisation of malto-oligosaccharides as models of the crystalline forms of starch: minimum chain-length requirement for the formation of double helices

The multigram preparation of malto-oligosaccharides of average d.p. ∼11, by the debranching of glycogen using Cytophaga isoamylase is described. Debranched glycogen and fractions derived therefrom readily crystallise from hot, concentrated aqueous solution to give 40–70% of crystalline materials having sharp X-ray diffraction patterns characteristic of A-, B-, and C-type (intermediate) starch polymorphs. The polymorphic form obtained is dependent on chain length, concentration, and temperature, the A-type being favoured by shorter chain-length, higher concentration, and higher crystallisation temperature. For pure oligomers, the minimum chain-length required for crystallisation (formation of double helices) is 10. In the presence of longer chains, oligomers as short as maltohexaose can co-crystallise. These results explain the known differences in aggregation properties of glycogens and amylopectins.     

Starch-branching enzymes preferentially associated with A-type starch granules in wheat endosperm

Two starch granule-bound proteins (SGP), SGP-140 and SGP-145, were preferentially associated with A-type starch granules (>10 microm) in developing and mature wheat (Triticum aestivum) kernels. Immunoblotting and N-terminal sequencing suggested that the two proteins were different variants of SBEIc, a 152-kD isoform of wheat starch-branching enzyme. Both SGP-140 and SGP-145 were localized to the endosperm starch granules but were not found in the endosperm soluble fraction or pericarp starch granules younger than 15 d post anthesis (DPA). Small-size starch granules (<10 microm) initiated before 15 DPA incorporated SGP-140 and SGP-145 throughout endosperm development and grew into full-size A-type starch granules (>10 microm). In contrast, small-size starch granules harvested after 15 DPA contained only low amounts of SGP-140 and SGP-145 and developed mainly into B-type starch granules (<10 microm). Polypeptides of similar mass and immunologically related to SGP-140 and/or SGP-145 were also preferentially incorporated into A-type starch granules of barley (Hordeum vulgare), rye (Secale cereale), and triticale (x Triticosecale Wittmack) endosperm, which like wheat endosperm have a bimodal starch granule size distribution.     

The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches

Physico-chemical properties of starch from wheat, rye, barley (waxy, high-amylose and normal-amylose), waxy maize, pea and potato (normal-amylose and high-amylopectin) were studied. Emphasis was given to the amylose (total, apparent and lipid-complexed) and amylopectin characteristics as well as to the gelatinization and retrogradation properties measured using differential scanning calorimetry. The total amylose content varied from ca. 1 % for waxy maize to 37% for high-amylose barley. The amylopectin characteristics were determined by high-performance size-exclusion chromatography after debranching with isoamylase. The weight-average degree of polymerization ( _w) was 26, 33 and 27 for the A-, B-, and C-type starches, respectively. In general, the potato starches exhibited the highest retrogradation enthalpies and the cereal starches the lowest, while the pea starch showed an intermediate retrogradation enthalpy. The data were analysed by principal component analysis (PCA). The _w showed positive correlation to the melting interval, the peak minimum, the offset temperatures of the retrogradation-related endotherm as well as to the gelatinization and retrogradation enthalpies. However, the high-amylose barley retrograded to a greater extent than the other cereal starches, despite low _w (24). The amylose content was negatively correlated to the onset and the peak minimum temperatures of gelatinization.     

Effects of structural imperfection on gelatinization characteristics of amylopectin starches with A- and B-type crystallinity

The aim of the present work was to investigate the effect of physical structures on the properties of starch granules. Starches with a high amylopectin content possessing A- and B-type crystallinity were chosen for the study. The gelatinization temperature decreased in the following order: maize (A) > potato (B) > wheat (A) > barley (A), which did not reflect a correlation with the type of crystallinity. Low values of gelatinization temperature were accompanied with high free surface energy of the crystallites. It is proposed that these data are caused by different types of imperfections in starch crystals. Annealing resulted in an enhancement of the gelatinization temperature and a decrease of the free surface energy of the crystallites for all starches reflecting a partial improvement of crystalline perfection. A limited acid hydrolysis (lintnerization) of the starches decreased the gelatinization temperature because of a partial disruption of the crystalline lamellae and an increase of the amount of defects on the edges of the crystallites. Annealing of the lintnerized starches improved the structure of maize and potato starch, giving them similar structural and physicochemical parameters, which was opposite the behavior of the annealed sample from wheat. The possible nature of removable and nonremovable defects inside the crystalline region of the starch granules is discussed. It is concluded that, besides the allomorphic A- and B-types of crystal packing, physical defects in the crystals possess a major impact on starch gelatinization.     

The new insight on ultrastructure of C-type starch granules revealed by acid hydrolysis

C-type starch granule could be considered as the mixture of A- and B-polymorphs. The ultrastructure of C-type starch granules has not been elucidated detailedly by comparison with that of A- or B-type starch. To better understand the ultrastructure of C-type starch granules, Environment Scanning Electron Microscope (ESEM) and Field Emission Gun Transmission Electron Microscope (FEG-TEM) have been used to analyze the conformation and ultrastructure of C-type starch granule from Rhizoma Dioscorea during acid hydrolysis. SEM results showed that the amorphous areas were mainly located interior part of C-type starch granules whereas the crystalline regions were found mostly in the peripheral region of the granules. The grain size can be confirmed to be about 4.5-9 nm from the HR-TEM micrographs. The nanocrystals from acid-thinned starch displayed the typical face-centered cubic structure. This selected area electron diffraction patterns showed that individual C-type starch granule consisted of A- and B-type polymorphs.     

Structural studies of starches with different water contents

The proportion of double helices in starches from a series of pea [rb, rug4-b, rug3-a, and lam-c mutants, and the wild type (WT) parental line], potato and maize (normal and low amylose), and wheat (normal) lines, ranged from about 30-50% on a dry weight basis. In relatively dry starch powders, only about half of the double helices were in crystalline order, this proportion being higher for A-type than for B-type starches. Using starch from WT pea as an example, it was found that increasing water content results in an increase in total crystallinity. When the water content was raised to a level similar to that in excess water, the proportion of crystallinity was close to the proportion of double helices (DH). Measuring crystallinity in starches with a high water content is difficult using traditional methods such as x-ray diffraction. A method was developed, therefore, for determining starch structural characteristics in excess water by measuring the enthalpy of gelatinization transition in quasi-equilibrium differential scanning calorimetry (DSC) experiments. It is suggested that DH% = DeltaH(sp)/DeltaH(DH) x 100%, where DeltaH(sp) and DeltaH(DH) represent the specific enthalpies of gelatinisation transition, DeltaH(sp) being measured as J/g dry starch weight and DeltaH(DH) as J/g DH, in starch. Studies on potato and maize starches in excess water and in 0.6M KCl showed, respectively, that DeltaH(DH) was 36.3 and 35.6 J/g for B-type polymorphs and 33.0 and 35.0 J/g for A-type polymorphs. For C-type starches, such as those from pea, intermediate values of DeltaH(DH), related to the proportions A-/B-polymorphs, should be used. The type of crystallinity in starch can be determined by the shift in peak temperature for thermograms in excess water and in excess 0.6M KCl. For B-polymorphs this shift was found to be approximately 2-3 degrees C and for A-polymorphs approximately 7-12 degrees C. The ratio between ordered areas with both A- and B-polymorphs can be determined from the enthalpies of disruption of each area. These enthalpies can be obtained by deconvolution of bimodal thermograms produced by C-type starches in excess 0.6M KCl. This methodical approach can be applied to all starches that give a sharp gelatinisation thermogram in excess water. Using a range of methods, including DSC, it was found that starch granules from the mutant peas are constructed in a similar way to those from the WT, with B-polymorphs in the centre and A-polymorphs at the periphery of all granules. The proportion of A/B-polymorphs, however, differed between the mutants. It was found that in addition to increasing the total crystallinity, increasing the water content within the granules also resulted in an increase in the proportion of B-polymorphs.     

Block-surface staining for differentiation of starch and cell walls in wheat endosperm.

A staining technique for differentiating starch granules and cell walls was developed for computer-assisted studies of starch granule distribution in cells of wheat (Triticum aestivum L.) caryopses. Blocks of embedded caryopses were sectioned, exposing the endosperm tissue, and stained with iodine potassium iodide (IKI) and Calcofluor White. Excessive tissue hydration during staining was avoided by using stains prepared in 80% ethanol and using short staining times. The IKI quenched background fluorescence which facilitated the use of higher concentrations of Calcofluor White. Cell wall definition was improved with the IKI-Calcofluor staining combination compared to Calcofluor alone. The high contrast between darkly stained starch granules and fluorescent cell walls permitted computer assisted analysis of data from selected hard and soft wheat varieties. The ratio of starch granule area to cell area was similar for both wheat classes. The starch granule sizes ranged from 2.1 microns 3 to 22,000 microns 3 with approximately 90% of the granules measuring less than 752 microns 3 (ca. 11 microns in diameter). Hard wheat samples had a greater number of small starch granules and a lower mean starch granule area compared to the soft wheat varieties tested. The starch size distribution curve was bimodal for both the hard and soft wheat varieties. Three-dimensional starch size distribution was measured for four cells near the central cheek region of a single caryopsis. The percentage of small granules was higher at the ends than at the mid-section of the cells.     

Structural transformations during gelatinization of starches in limited water: combined wide- and small-angle X-ray scattering study

Rice flour (18-25% moisture) and potato starch (20% moisture) were heated with continuous recording of the X-ray scattering during gelatinization. Rice flours displayed A-type crystallinity, which gradually decreased during gelatinization. The development of the characteristic 9 nm small-angle X-ray scattering (SAXS) peak during heating at sub-gelatinization temperatures indicated the gradual evolution into a stacked lamellar system. At higher temperatures, the crystalline and lamellar order was progressively lost. For potato starch (B-type crystallinity), no 9 nm SAXS peak was observed at ambient temperatures. Following the development of lamellar structures at sub-gelatinization temperatures, B-type crystallinity and lamellar order was lost during gelatinization. On cooling of partially gelatinized potato starch, A-type crystallinity steadily increased, but no formation of stacked lamellar structures was observed. Results were interpreted in terms of a high-temperature B- to A-type recrystallization, in which the lateral movement of double helices was accompanied by a shift along their helical axis. The latter is responsible for the inherent frustration of the lamellar stacks.     

粉末X射线衍射图谱计算植物淀粉结晶度方法的探讨

植物淀粉有A-型、B-型和C-型3种晶体。以水稻(Oryza sativa)、马铃薯(Solanum tuberosum)、豌豆(Pisum sativum) 和莲藕(Nelumbo nucifera)淀粉为材料, 利用粉末X-射线衍射仪(XRD)调查了不同晶体类型淀粉的波谱特征, 探讨XRD波谱相对结晶度的计算方法。软件峰拟合法、软件曲线法、直线作图法和曲线作图法均可用于计算淀粉XRD波谱的相对结晶度, 以曲线作图法计算结果较为可靠。利用曲线作图法得出的结果表明, 稻米淀粉的结晶度与直链淀粉含量呈显著线性负相关, 酸解莲藕淀粉的结晶度与淀粉酸水解度呈显著线性正相关。酸水解使莲藕淀粉的C-型晶体转变为A-型晶体。上述研究结果为利用XRD分析植物淀粉晶体类型和计算相对结晶度提供了重要参考。     

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.     

Genetic elimination of a starch granule protein, SGP-1, of wheat generates an altered starch with apparent high amylose

A starch granule protein, SGP-1, is a starch synthase bound to starch granules in wheat endosperm. A wheat lacking SGP-1 was produced by crossing three variants each deficient in one of three SGP-1 classes, namely SGP-A1, -B1 or -D1. This deficient wheat (SGP–1 null wheat) showed some alterations in endosperm starch, meaning that SGP-1 is involved in starch synthesis. Electrophoretic experiments revealed that the levels of two starch granule proteins, SGP-2 and -3, decreased considerably in the SGP-1 null wheat though that of the waxy protein (granule-bound starch syn- thase I) did not. The A-type starch granules were deformed. Apparent high amylose level (30.8–37.4%) was indicated by colorimetric measurement, amperometric titration, and the concanavalin A method. The altered structure of amylopectin was detected by both high- performance size-exclusion chromatography and high-performance anion exchange chromatography. Levels of amylopectin chains with degrees of polymerization (DP) 6–10 increased, while DP 11–25 chains decreased. A low starch crystallinity was shown by both X-ray diffraction and differential scanning calorimetry (DSC) analyses because major peaks were absent. Abnormal crystallinity was also suggested by the lack of a polarized cross in SGP-1 null starch. The above results suggest that SGP-1 is responsible for amylopectin synthesis. Since the SGP-1 null wheat produced novel starch which has not been described before, it can be used to expand variation in wheat starch. Received: 30 April 1999 / Accepted: 9 November 1999     

Effect of α-Amylase Degradation on Physicochemical Properties of Pre-High Hydrostatic Pressure-Treated Potato Starch

The effect of high hydrostatic pressure (HHP) on the susceptibility of potato starch (25%, w/v) suspended in water to degradation by exposure to bacterial α-amylase (0.02%, 0.04% and 0.06%, w/v) for 40 min at 25°C was investigated. Significant differences (p < 0.05) in the structure, morphology and physicochemical properties were observed. HHP-treated potato starch (PS) exposed to α-amylase (0.06%, w/v) showed a significantly greater degree of hydrolysis and amount of reducing sugar released compared to α-amylase at a concentration of 0.04% (w/v) or 0.02% (w/v). Native PS (NPS) granules have a spherical and elliptical form with a smooth surface, whereas the hydrolyzed NPS (hNPS) and hydrolyzed HHP-treated PS granules showed irregular and ruptured forms with several cracks and holes on the surface. Hydrolysis of HHP-treated PS by α-amylase could decrease the average granule size significantly (p <0.05) from 29.43 to 20.03 μm. Swelling power decreased and solubility increased with increasing enzyme concentration and increasing pressure from 200–600 MPa, with the exception of the solubility of HHP-treated PS at 600 MPa (HHP₆₀₀ PS). Fourier transform infrared spectroscopy (FTIR) showed extensive degradation of the starch in both the ordered and the amorphous structure, especially in hydrolyzed HHP₆₀₀ PS. The B-type of hydrolyzed HHP₆₀₀ PS with α-amylase at a concentration 0.06% (w/v) changed to a B+V type with an additional peak at 2θ = 19.36°. The HHP₆₀₀ starch with 0.06% (w/v) α-amylase displayed the lowest value of T _o (onset temperature), T _c (conclusion temperature) and ΔH _gel (enthalpies of gelatinization). These results indicate the pre-HHP treatment of NPS leads to increased susceptibility of the granules to enzymatic degradation and eventually changes of both the amorphous and the crystalline structures.     

荔枝核淀粉特性研究

本文采用扫描电镜观察荔枝核淀粉颗粒呈椭圆或多边形。差示扫描量热仪分析荔枝核淀粉的热力学特性表明,其起始温度、峰温度、终止温度和吸热焓值分别为69．04℃、78．79℃、87．08℃和7．5J/g。X射线衍射分析表明荔枝核淀粉呈C型结晶。Brabender粘度分析表明荔枝核淀粉糊化温度为85．3℃,淀粉糊高温稳定。     

Differences of Starch Granule Distribution in Grains from Different Spikelet Positions in Winter Wheat

Wheat starch development is a complex process and is markedly difference by changes in spikelet spatial position. The present study deals with endosperm starch granule distribution and spatial position during filling development. The study was conducted with pure starch isolated from wheat (Triticum aestivum L.), Jimai20 and Shannong1391, at 7–35 days after anthesis (DAA). The results showed that grain number, spikelet weight and grain weight per spikelet in different spatial position showed parabolic changes. Upper spikelets had highest starch and amylose content followed by basal spikelets, then middle spikelets. The paper also suggested the volume percents of B-type and A-type granule in grain of middle spikelets were remarkably higher and lower than those of basal and upper spikelets, respectively. However, no significant difference occurred in the number percents of the two type granule. The ratio of amylase to amylopectin was positively correlated with the volume proportion of 22.8–42.8 µm, but was negatively related to the volume proportion of <9.9 µm. The results indicated that the formation and distribution of starch granules were affected significantly by spikelet position, and grains at upper and basal spikelet had the potential of increasing grain weight through increasing the volume of B-type granules.