| Research Abstract |
Amylopectin is a major constituent of starch, being about 80%, in rice and therefore, will be expected to affect greatly on the eating quality of cooked rice and the processing properties for industrial use. In spite of this importance, little attention has, so far, put on amylopectin in rice breeding, because of limited numbers of the information for related genes modifying amylopectin structure and of the genetic resources in amylopectin. In this research, we tried to induce the mutants for amylopectin by MNU treatment of fertilized egg cells in rice and to characterize the genetic and physicochemical properties for using them as breeding materials.
We developed and devised the speedy and simplified methods for the iodine colorimetric measurement of starch/iodine complex using the microprocessor controlled diode array spectrograph DU 7000 Spectrophotometer (Beckman), SDS-PAGE analysis of starch biosynthesis related enzyme proteins, Native-PAGE/Activity staining for amylopectin biosynt
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hesis related enzymes such as starch branching enzymes, starch debranching enzymes, starch synthase and pullanase, and the measurement of starch gelatinization using urea. Using these methods, we screened the mutant strains induced by MNU treatment of fertilized egg cells of three kinds of two Japonica rice cultivar, Kinmaze and Taichung 65, and a Indica rice cultivar IR36, and obtained various kinds of mutants modifying the amylopectin structure of endosperm starch, such as amylose extender (ae), floury 1(flo 1), floury 2(flo 2), floury 3(flo 3), floury 4(flo 4), sugary 1(sug 1) etc. The structural and physicochemical analyses of endosperm starches in these mutants shows that the changes in branching structure of amylopectin modified more greatly than the amylose content on the processing properties of starch such as the gelatinization or swelling of starch, which greatly affects the cooking quality of boiled rice and the industrial processing quality of rice starch. These facts indicates strongly the great importance of genetic resources for amylopectin in the breeding to improve the grain quality in rice. The results obtained in this research will play the important rolls not only as breeding materials improving the grain quality in rice but also as the materials of academic researches comprehending the genetic and biochemical regulation of amylopectin biosynthesis. Less
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