Naoyoshi Inouchi

Natural variation in rice starch synthase IIa affects enzyme and starch properties

The natural variation in starch synthase IIa (SSIIa) of rice (Oryza sativa L.) was characterised using near-isogenic lines (NILs). SSIIa is a candidate for the alk gene regulating the alkali disintegration of rice grains, since both genes are genetically mapped at the same position on chromosome 6 and related to starch properties. In this study, we report that the alkali-susceptible cultivar Nipponbare lacked SSIIa activity in endosperm. However, the activity was detected with NILs having the alk allele of alkali-tolerant Kasalath. SSIIa protein was present even in Nipponbare endosperm, but it was not associated with starch granules at the milky stage of endosperm. Three single-nucleotide polymorphisms (SNPs) predicting amino acid substitutions existed between the cDNA sequences of SSIIa of Nipponbare and Kasalath were genotyped with 65 rice cultivars and four wild relatives of cultivated rice. The results obtained explain the potential importance of two of the amino acid residues for starch association of rice SSIIa. An analysis of the chain-length distribution of β-limit dextrin of amylopectin showed that without SSIIa activity, the relative number of A-chains (the short chains without branches) increased and that of B1-chains (the short chains with branches) decreased. This suggests that, given the SSIIa defect, short A-chains could not reach a sufficient length for branching enzymes to act on them to produce B1-chains.

The effect of environmental temperature on distribution of unit chains of rice amylopectin

The effects of environmental temperature during the early development of seeds on the structural characteristics of the endosperm starch were investigated using near-isogenic lines of rice plants (Taichung 65, waxy), grown under temperature controlled conditions. High performance gel permeation chromatography (HPLC) demonstrated that Pseudomonas isoamylase-debranched amylopectins of rice plants grown at lower temperature (25 °C) contain increased amounts of short chains and decreased amounts of long chains as compared with amylopectins obtained from rice plants grown at higher temperature (30°C). By high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) of isoamylase-debranched amylopectins it was detected that the amount of unit chains with degree of polymerization (DP) 6 and 11-13, in the amylopectin of rice plants grown at lower temperature (25°C) had significantly increased and the amount of unit chains with DP 8, 22-24 and 29 had significantly decreased, as compared with the amylopectin of rice plants grown at higher temperature (30°C ). It was confirmed that the environmental temperature between 5 and 10 d after pollination strongly influenced the structure characteristics of the endosperm starch of rice plants.

Effects of Variations in Starch Synthase on Starch Properties and Eating Quality of Rice

Abstract We evaluated the effects of functional variation in three starch synthases in rice (Oryza sativa L.)−granule-bound starch synthase I (GBSSI, wx), starch synthase I (SSI, SSI), and starch synthase IIa (SSIIa, alk)−between indica cultivar Kasalath and japonica cultivar Nipponbare on starch properties and eating quality. We used three near-isogenic lines−NIL(Wxa), NIL(SSI k), and NIL(Alk)−containing chromosomal segments of Kasalath on a Nipponbare genetic background. The Wxa allele explained most of the difference in amylose content between the two cultivars, and decreased the peak viscosity and breakdown to less than half of those of Nipponbare. These changes reduced the quality of cooked rice both just after cooking and after storage at 5ºC. The variation in SSIIa also affected the eating quality after storage of cooked rice at 5ºC : NIL(Alk) became harder and less sticky than Nipponbare, although the rices were comparable just after cooking. Differential scanning calorimetry revealed faster retrogradation of the once-gelatinized starch in NIL(Alk). The variation in SSI alleles hardly affected these properties.

Genetic Analysis of Long Chain Synthesis in Rice Amylopectin

The amount of long chains (LC) of amylopectin in high-amylose rice is thought to be one of the important determinants of its quality when cooked. A wide range of differences in LC content have been reported in rice varieties, which can be clearly divided into four classes based on LC and apparent amylose content: namely, amylose and LC-free, low or medium-amylose and low-LC, high-amylose and medium-LC, high-amylose and high-LC. However, genetic factors controlling LC content have not been fully understood. Here, we performed quantitative trait loci (QTL) analysis of LC content using 157 recombinant inbred lines (RILs) derived from a cross of a low-LC cultivar, Hyogokitanishiki, and a high-LC line, Hokuriku 142. By analyzing randomly selected 15 RILs, it was shown that high LC content (≥11%) was associated with high setback viscosity (≥200 RVU), and that low LC (≤ 3%) was associated with low setback viscosity (≤ 130 RVU), as measured by a Rapid Visco Analyzer. With setback viscosity as an indicator for LC content, QTL analysis was conducted using 60 DNA markers including a CAPS marker that distinguished Wxa and Wxb alleles coding for granule-bound starch synthase I (GBSSI or Wx protein), the enzyme working for amylose biosynthesis. Only one QTL with a peak log of likelihood score at the wx locus was detected, and no line showing setback viscosity corresponding to the medium-LC class appeared. The fact that wx mutants of Hokuriku 142 lacked LC in their rice starch supports the view that the functional Wx allele is indispensable for LC synthesis in addition to amylose synthesis in rice endosperm. We suggest three possible reasons why no line with medium-LC content was observed. First, the locus (loci) responsible for generation of medium-LC may be located very close to the wx locus and not able to be dissected by the population and DNA markers we used. Second, there may be special QTLs for medium-LC cultivars that do not exist in low- or high-LC cultivars. Third, medium-LC cultivars may have an as-yet unidentified Wx allele with lower capability in LC synthesis compared to the Wx allele in high-LC cultivars.

Structural and Retrogradation Properties of Rice Endosperm Starch Affect Enzyme Digestibility of Steamed Milled-Rice Grains Used in Sake Production

ABSTRACT Structural and physicochemical characteristics of endosperm starch from milled rice grains of seven Japanese cultivars used in sake production were examined. Amylose content was 15.2–20.2%, number-average degree of polymerization (DPn) of amylose was 900–1,400, and the ratio of short-to-long chain amylopectin was 2.7–3.5, respectively. The degree of retrogradation of purified starch stored for seven days at 4°C after gelatinization was 20–31%. The degree of retrogradation correlated negatively with the ratio of short-to-long chain amylopectin. The effect of holding time after steaming on enzyme digestibility and starch retrogradation of steamed rice grains was investigated. The longer the holding time after steaming, the greater the extent of retrogradation, and the less the degree of enzymatic digestibility. The decreased rate of enzyme digestibility correlated with amylopectin chain length distribution. Samples with short-chain amylopectin exhibited a slow decrease in enzyme digestibility. It w...

Structural and Physicochemical Properties of Endosperm Starches Possessing Different Alleles at the Amylose-extender and Waxy Locus in Maize (Zea mays L.)

The structure and some physicochemical properties of endosperm starches from seven amylose-extender (ae) and two waxy (wx) alleles of maize (Zea mays L.) were studied. Starches prepared from mature kernels of six ae mutants, Oh43 inbred line ae (standard ae), ae-RWB-2 and ae-RWB-3, and W23 x L317 hybrid line ae-PP, ae-Bol 561 and ae-emll, were uniquely ae type, as was concluded from B type X-ray diffractograms; high gelatinization temperatures determined by differential scanning calorimetry (DSC); with poor starch-granule digestibility to amylase; high amylose (37-45 %) and high intermediate fraction (13-18%) contents; and low ratios (1.0-1.2) of long α-1,4-chains to short α-1,4-chains of amylopectin determined by gel permeation chromatography (GPC) of isoamylase-debranched starches. The results also indicated that different ae alleles had different effects on the amylose content of endosperm starches. Mature kernels of Oh43 ae-RWB-1 mutant showed tarnished and translucent phenotype characteristics of the ae genotype but contained endosperm starch with 21-22% of amylose which was lower than that of the Oh43 normal counterpart. Both wx-B and wx-C (standard wx) genes have similar effect on structure and physicochemical properties of waxy starches of A632, B37, C105, Oh43, and W64A inbred lines.

Functions of Gum Arabic and Soybean Soluble Polysaccharide in Cooked Rice as a Texture Modifier

The textural properties of cooked rice were investigated in the presence and the absence of gum arabic (GA) and soybean soluble polysaccharide (SSPS). SSPS was more effective in increasing the hardness and in decreasing the stickiness of the rice grains than GA. For both polysaccharides, the increase in hardness was more apparent in the whole body than at the periphery, whereas the decrease in stickiness was more apparent at the periphery than in the whole body. SSPS was more effective in retarding the gelatinization of rice starch and in lowering the elastic characters of the glutinous layer (the materials leached out of the rice grains during cooking) along with a decrease in the amount of amylopectin leached. The textural hardness of cooked rice was determined by the degree of starch gelatinization, whereas the textural stickiness was related to the rheological characters of the glutinous layer and the leaching profile of the starch components.

The genetic effects on some physico-chemical properties of starch granules

Publisher Summary The properties of starch from plants mainly depend on plant species and genetic factors. The shape, size, crystallinity, gelatinization temperatures, enzymatic susceptibilities, amylose contents, and chain-length distributions of amylopectins of starch granules differ for various genotypes and plant species. This chapter explores the study of some properties of commercial starches (with defined sources) of several plant species, and normal type (wild type) and two kinds of mutant maize starches, so that genetic effects and the effect of plant species on the properties of starch can be identified.. The chapter also illustrates the differences in the unit-chain length distributions of debranched amylopectins in starches of several plant species with comparison to normal maize amylopectin by HPAEC-PAD. Subsequently, the chapter summarizes some physico-chemical properties of starches of several plant species. The peak temperature of gelatinization of the ae maize starch determined by DSC was higher and that of su2 maize starch was lower than that of the other starches. The peak viscosity measured by RVA and swelling power of potato and sweet potato starches were higher than those of cereal starches. The results indicate that the hot water absorption ability of starch granules of sweet potato and potato is larger than cereal starch granules. Moreover, the viscosity potato and sweet potato starch is higher than those of cereal starches. The peak viscosity (RVA) and swelling power of the ae starch granules were lower than those of other starches.