46. Genic and temperature effects on starch structure of high-amylose mutants of rice

1) Hokuriku National Agricultural Experiment Station, Joetsu, Niigata, 943-01 Japan

High-amylose mutants of rice have been found among mutant lines induced by chemical mutagen treatment (Satoh and Omura 1981; Yano et al. 1985). The present paper describes the further analysis on the structure of endosperm starches and the effect of temperature on the starch structure of high-amylose mutants.

Eight high-amylose mutant lines and the original cultivar, Kinmaze, were planted at Tsukuba, Japan. Out of them, four mutant lines, EM-10, -16, -72 and -129, are known to carry the ae gene at the same locus. One of the mutant lines, EM-129, and the control were grown at five different locations in Japan, i.e., Tsukuba, Joetsu, Kyoto, Kurashiki and Fukuoka, to assess environmental changes in starch structure. Starch granules were prepared from the endosperms of these materials. Isoamylase-debranched starch components were fractionated by gel filtration on Toyo-pearl HW 50 SF and HW 55 SF columns.

The starches of high-amylose mutants contained amylose (Fr. I) ranging from 24 to 31%, as compared with 23% of the control. Fractions II and III (Fr. II and Fr. III) shown in Table 1 are considered to be derived from a-1,4 chains of amylopectin molecules. Fr. II comprises long B chains and Fr. III is the mixture of short B chains and A chains of amylopectin. Therefore, the relative ratio of Fr. III to Fr. II indicates a tentative determinant for the fine structure of amylopectin. The Fr. IIJ/Fr. II ratios in the mutants were 1.2 to 1.6, whereas 2.7 in the control, suggesting the structural difference of amylopectin between the mutants and the control. Also, the mutants were characterized by an increased content of intermediate fraction which eluted in- between Fr. I and Fr. II. These results indicate that the starch of high- amylose mutants consist of anomalous amylopectin having a larger amount of longer chains than the normal amylopectin.

The amylose content in both the high-amylose mutants and the control was negatively correlated with the average daily temperature during the 20 days after heading (Table 2). The temperature effect on amylose content accords with the results obtained in glutinous and nonglutinous isogenic lines (Asaoka et al. 1985) and du mutants (Okuno 1985; Sano et al. 1985). However, the distribution of unit chain length of amylopectin in the ae mutant was unaffected by temperature, in disagreement with the results obtained in Wx-wx isogenic lines and du mutants. This suggests that gene expression in the region of the ae locus, encoding the branching enzyme responsible for the formation of branch points of amylopectin, is not modified by the temperature during the grain filling period.

Table 1. Distribution of isoamylase-debranched materials of endosperm starches from high amylose mutants of rice

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Okuno, K., 1985. Environmental control of gene expression in endosperm mutants of rice. RGN 2: 65-66.

Sano, Y., M. Maekawa H. Kikuchi, 1985. Temperature effects on the Wx protein level and amylose content in the endosperm of rice. J. Heredity 76: 221-222.

Satoh, H. and T. Omura, 1981. New endosperm mutations induced by chemical mutagens in rice, Oryza sativa L.. Jpn. J. Breed. 31: 316-326.

Yano, M., K. Okuno, J. Kawakami, H. Satoh and T. Omura, 1985. High amylose mutants in rice, Oryza sativa L. Theor. Appl. Genet. 69: 253-257.