Submitted to: Plant Physiology
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1998
Publication Date: N/A
Technical Abstract: Starch is composed of a mixture of 20 to 30% amylose (with 0.1% branch points) and 70 to 80% amylopectin (with about 4%branch points). The biochemical pathway for starch biosynthesis has been inferred from many biochemical and genetic studies. Elucidation of the roles of enzymes involved in starch biosynthesis has been complicated by a great deal of redundancy. In maize, biochemical and genetic evidence both suggest that there are at least five starch synthases, two debranching enzymes and several pyrophosphorylases. In the present study, we measured carbon isotope ratios of amylose and amylopectin components of corn starch and also isolated starch from different maize mutants known to have genetic lesions in the starch biosynthetic pathway. Carbon isotope ratios of the amylose fraction indicated that they were less negative than those of the amylopectin fraction. An identical pattern in carbon isotope ratios was also observed in starch isolated from mutants that either lack amylose or contain more amylose. Carbon isotope ratios of starch isolated from potato and barley also exhibited the same pattern but the magnitude of the difference was more pronounced in these plants. We believe that carbon isotope ratio analyses of starch and starch fractions would not only yield information about the type and number of enzymes involved in starch biosynthesis, but also would establish their specific roles.