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Starch Characteristics of the Rice Mutant du2-2 Taichung 65 Highly Affected by Environmental Temperatures During Seed Development

¹National Institute of Crop Science, Kannondai, Tsukuba, Ibaraki 305-8518, Japan. ²Corresponding author. Phone: +81-29-838-8951. Fax: +81-29-838-8951. E-mail: suzuyasu@affrc.go.jp. ³Graduate School of Agriculture, Hokkaido University, Kita 9, Nishi 9, Kita-ku, Sapporo 060-8589, Japan. ⁴National Agricultural Research Center, Kannondai, Tsukuba, Ibaraki 305-8666, Japan. ⁵National Food Research Institute, Kannondai, Tsukuba, Ibaraki 305-8642, Japan. ⁶Graduate School of Agriculture and Life Sciences, University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.

The effects of environmental temperature (21 vs. 28°C) during rice seed development on the starch characteristics (apparent amylose content, amylopectin chain length distribution, and gelatinization properties) of nonwaxy Taichung 65 (T65), waxy Taichung (T65wx), du2-2 mutated low-amylose strain Taichung (76-3/T65), and Koshihikari were studied. Amylose contents increased with decreasing environmental temperatures. Analysis of the amylopectin chain length distribution showed that the relative amounts of long chains with degree of polymerization (DP) > 25 in all starches decreased if maturation occurred at 21°C. Gelatinization onset, peak, and conclusion temperatures and enthalpies decreased with decreasing environmental temperatures. Of all starches studied, the du2-2 mutated low-amylose Taichung (76-3/T65) was most affected by maturation temperatures. These results indicate that the du2-2 mutated low-amylose Taichung (76-3/T65) may be a useful strain in understanding biochemical and genetic starch biosynthesis response to slight changes in temperature.