[14C]Sucrose Uptake and Labeling of Starch in Developing Grains of Normal and segl Barley

Publisher Website
Google Scholar
Abstract
Previous work showed that the seg1 mutant of barley did not differ from normal Betzes in plant growth, photosynthesis or fertility, but it produced only shrunken seeds, regardless of pollen source. To determine whether defects in sucrose uptake or starch synthesis resulted in the shrunken condition, developing grains of Betzes and seg1 were cultured in [14C]sucrose solutions after slicing transversely to expose the endosperm cavity and free space. In both young grains (before genotypes differed in dry weight) and older grains (17 days after anthesis, when seg1 grains were smaller than Betzes), sucrose uptake and starch synthesis were similar in both genotypes on a dry weight basis. To determine if sucrose was hydrolyzed during uptake, spikes of Betzes and seg1 were allowed to take up [fructose-U-14C]sucrose 14 days after anthesis and the radioactivity of endosperm sugars was examined during 3 h of incubation. Whereas less total radioactivity entered the endosperm and the endosperm cavity (free space) of seg1, in both genotypes over 96% of the label of endosperm sugars was in sucrose and there was no apparent initial or progressive randomization of label among hexose moieties of sucrose as compared to the free space sampled after 1 h of incubation. The seg1 endosperms are apparently capable of normal sucrose uptake and starch synthesis and hydrolysis of sucrose is not required for uptake in either genotype. Evidence suggests abnormal development of grain tissue of maternal origin during growth of seg1 grains.