Grain-filling Temperature of Rice Influences the Content of Super-long Chain of Amylopectin and its Unit-chain Distribution

Abstract

The influence of the grain-filling temperature of rice on the super-long chain (LC) content of amylopectin and its chain-length distribution was examined by the fluorescent labeling/HPSEC method. The LC content of Kirara 397, which is the main cultivar in Hokkaido, was 2.58, 1.30 and 0.48% for the grain-filling temperature (°C, day/night) of L21/17, M25/21 and H29/25, respectively. The lower temperature increased the LC content and also the molar and weight ratios (A+B1)/(B2+B3) of amylopectin unit-chains. These findings were confirmed by the experiment for five varieties and four lines of rice recently bred in Hokkaido and Milky Queen, cultivated at the grain-filling temperature of L22/16, M26/20, H30/24 and HH34/28. From the LC contents at 19, 23, 27 and 31°C (average temperature of day and night) the increase of LC content per 1°C was determined to be 0.542 0.152 and 0.037%/°C for the temperature ranges of 19-23, 23-27 and 27-31°C, respectively. This clarified that the lower temperature increased the LC content more, as in the case of the apparent amylose content (Amylose+Amylopectin LC). The proportion of the LC in the apparent amylose content was larger for low-amylose varieties than for non-glutinous varieties. Less varietal difference in the LC content among the varieties and lines was observed under the grain-filling temperature. Therefore, the target of rice breeding for cooked rice with good texture appeared to be the low LC content of amylopectin with stable structure against grain-filling temperature. This might be achieved by the gene analysis of enzyme(s) involved in the biosynthesis of amylopectin LC.