Abstract
In wheat grains, the assimilate is transferred from the dorsal vascular bundle into endosperm tissue in turn via nucellar projection, endosperm cavity, and modified aleurone cells (transfer cells in endosperm tissue). Structural changes in grain tissues at the early ripening stage were assessed using light microscopy to elucidate the relations of assimilate transfer to development. Wheat plants of “NORIN61” variety were cultivated in a research field at the College of Agriculture, Ibaraki University. After preparation through double fixation with glutaraldehyde and osmium tetroxide, grains were embedded in Spurr resin. Semi-thin sections were cut and stained with toluidine blue O. Differentiation of endosperm tissue (sink) was completed by 8 days after flowering. Structures for assimilate transfer from the nucellar projection to the endosperm cavity and modified aleurone cells developed during that stage. At 9 days after flowering, transfer cells were developed at the nucellar projection, indicating structural changes for efficient assimilate transfer from the dorsal vascular bundle to the endosperm cavity. Large amyloplasts that had accumulated remarkably in the endosperm indicated an increased rate or amount of assimilate transfer from the dorsal vascular bundle, which changes its cell arrangement to exert its function maximally, thereby adapting to the period of active assimilate transfer.
