The characteristics and fate of the soybean inner nucellus

Development of the soybean inner nucellus is described. The inner nucellus is a distinct region composed of cells that stain darkly with toluidine blue oxide and have thickened walls when compared with the remaining nucellus. This tissue region becomes apparent during early megasporogenesis and completely surrounds the expanded megasporocyte, megaspores and 2- and 4-nucleate megagametophytes. By the time the megagametophyte is cellular the inner nucellus is restricted to the chalazal end of the megagametophyte. The cells of the inner nucellus of soybean exhibit a normal ultrastructural appearance with an elevated concentration of ribosomes and numerous plasmodesmatal connections among themselves, to cells of the outer nucellus and to the developing and cellular megagametophyte. Our observations suggest that the inner nucellus of soybean may provide metabolites for the developing megagametophyte.