Movement of C-Labeled Assimilates into Kernels of Zea mays L: I. Pattern and Rate of Sugar Movement.

Carbon-14, photosynthetically fixed in leaves of Zea mays L. and translocated to developing kernels, passed through specialized basal endosperm cells prior to movement into the starchy endosperm and embryo. Radioactivity migrated in the endosperm at a maximum rate of 2.7 millimeters per hour, and there was no difference in the rate of movement in kernels treated 14 to 30 days after pollination.Sucrose contained over three-fourths of the radioactivity in the kernal base (fruit stalk) 1 to 6 hours after (14)CO(2) treatment of the plant. Conversely, in the basal endosperm three-fourths of the radioactivity was in glucose and fructose. A high proportion of the radioactivity was retained in the monosaccharides of the starchy endosperm the first 3 hours after the (14)CO(2) treatment. With additional time after treatment there was a decline in the percentage of radioactivity in the monosaccharides and an increase in sucrose-(14)C. From these data we suggest that translocated sucrose is cleaved to glucose and fructose during entry into the endosperm and that the monosaccharides diffuse throughout the endosperm. Once the sugars arrive in the cells active in starch synthesis, they are rapidly converted to sucrose which in turn is utilized in the synthesis of starch.