Grain-filling temperature of rice [Oryza sativa] influences the content of super-long chain of amylopectin and its unit-chain distribution
2008
Igarashi, T.(Hokkaido. Kamikawa Agricultural Experiment Station, Pippu (Japan)) | Kanda, H. | Kinoshita, M.
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 (degC, day/night) of L 21/17, M 25/21 and H 29/25, 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-filing temperature of L 22/16, M 26/20, H 30/24 and HH 34/28. From the LC contents at 19, 23, 27 and 31degC (average temperature of day and night) the increase of LC content per 1degC was determined to be 0.542 0.152 and 0.037%/degC for the temperature ranges of 19-23, 23-27 and 27-31degC, 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.
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