Movement of C-labeled Assimilates into Kernels of Zea mays L: III. AN ANATOMICAL EXAMINATION AND MICROAUTORADIOGRAPHIC STUDY OF ASSIMILATE TRANSFER

Basal tissue of developing maize kernels was examined by light micros-copy and by scanning and transmission electron microscopy. Plasmodesmata occur in pedicel and endosperm parenchyma but were not seen between the placento-chalazal cells and basal endosperm transfer cells. A layer of noncellular material separates the transfer cells from the placentochalazal cells. Microautoradiography of ¹⁴C-labeled assimilates entering the kernels revealed that incoming sugars are not confined to the apoplast, but rather are present in the cytoplasm and vacuoles of pedicel and endosperm cells. No specific accumulation of radioactivity was seen in any particular tissue, although at later sampling times, a higher grain density in the pedicel than the endosperm indicated a general buildup of sugars in the pedicel. A possible model for sugar movement into developing kernels is discussed.