| Summary: | Mutant alleles at five rugosus loci (r, rb, rug-3, rug-4 and rug-5) were examined for their effects on the growth and starch content of the pea seed. In order to study gene interaction double mutants between pairs of rugosus loci were produced. In addition, starch extracted from the single mutant lines was examined for structural differences. The primary effect of the r mutation was to reduce the production of amylopectin in the developing embryo. This led to decreased starch in the embryo, but an increased proportion of amylose in the starch. Starch grains in the mutant embryo differentiated from 'simple' to 'compound' during development. The primary effect of both the rb and rug-4 mutations was to reduce carbon flux through the starch biosynthetic pathway. This led to a decreased starch content in the embryo during development and in the mature seed. The proportion of amylose in the starch also was reduced, in relation to the reduction in starch. In addition the rb mutation caused a reduction in the amount of starch accumulated in the testa during development. The rug-3 mutation acted as a complete block on starch synthesis in both the embryo and testa throughout development. Reciprocal F, crosses indicated that there was a maternal effect of both the rb and rug-3 mutations on final seed size. The rug-5 mutation also blocked starch synthesis, but only late in development when the embryo began to dry. In addition, the mutation altered the appearance of the starch grains, which were irregular in appearance throughout embryo development. The fine structure of amylopectin was studied by enzymically debranching amylopectin and separating the constituent chains by HPLC. Only the rand rug-5 genes were demonstrated to affect amylopectin structure. The effect of the r gene was minor, however, the rug-5 mutation caused a fundamental alteration in amylopectin structure.
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