A rice Wx gene encoding a granule-bound starch synthase I (GBSSI) was introduced into the null-mutant waxy (wx) rice, and its effect on endosperm starches was examined. The apparent amylose content was increased from undetectable amounts for the non-transgenic wx cultivars to 21.6-22.2% of starch weight for the transgenic lines. The increase was in part due to a significant amount of extra-long unit chains (ELCs) of amylopectin (7.5-8.4% of amylopectin weight), that were absent in the non-transgenic wx cultivars. Thus, actual amylose content was calculated to be 14.9-16.0% for the transgenic lines. Only slight differences were found in chain-length distribution for the chains other than ELCs, indicating that the major effect of the Wx transgene on amylopectin structure was ELC formation. ELCs isolated from debranched amylopectin exhibited structures distinct from amylose. Structures of amylose from the transgenic lines were slightly different from those of cv. Labelle (Wx(a)) in terms of a higher degree of branching and size distribution. The amylose and ELC content of starches of the transgenic lines resulted in the elevation of pasting temperature, a 50% decrease in peak viscosity, a large decrease in breakdown and an increase in setback. As yet undetermined factors other than the GBSSI activity are thought to be involved in the control of formation and/or the amount of ELCs. Structural analysis of the Wx gene suggested that the presence of a tyrosine residue at position 224 of GBSSI correlates with the formation of large amounts of ELCs in cultivars carrying Wx(a).

Waxy rice is used for staple and processed foods, and for its effective breeding an evaluation selection index has been required. Here, the chain-length distribution of amylopectin from japonica waxy rice varieties with different hardness of rice cake were analyzed by the fluorescent labeling HPSEC method, and the relation of the unit chain-length distribution to the hardness was examined. The difference among varietals was found in the amylopectin structure. Waxy rice producing soft cake, such as Hakuchoumochi, has more short chains (A B 1), and fewer long chains (B 2 B 3), than that producing hard cake, such as Koganemochi. The molar ratio of short chains (A B 1) long chains (B 2 B 3), which is considered to be the number of chains comprising a cluster of amylopectin, was 10.1 11.7, being different among the varieties tested. The molar ratio determined by fluorescent response was much more reliable than the weight ratio determined by IR response because of the stable base line during HPLC. A negative correlation was found between the molar ratio and the hardening of rice cake. Therefore, the molar ratio (A B 1) (B 2 B 3) of amylopectin unitchains seemed to be one of useful evaluation selection indexes for breeding of waxy rice. An index, or molar ratio, lower than 11 appeared to be suitable for processing use, and one higher than 11.5 for principal food use.

No abstract

No abstract

五十嵐俊成 1) ・柳原哲司 1) ・神田英毅 2) ・川本和信 3) ・政木一央 3)( 1) 北海道立上川農業試験場， 2) 北海道米麦改良協会， 3) ビーエルテック株式会社) 要旨：水稲育種におけるアミロース含有率の測定は，一般にオートアナライザーを利用したヨード呈色法で単一波長 620 nm で行われている．我々はヨウ素吸収曲線(波長 400 nm-900 nm)を自動測定できるマルチチャンネル検出器