Abstract
Histological changes in the developing rice endoperm and nucellus were observed with attention to the translocation pathway of reserve substances. Results were discussed by comparison with those of two-rowed barley which reported in the previous papers. 1. On the young endosperm (9-10 days after anthesis), some irregular shaped cells were found in the midway area between peripheral and center of the lateral portions. However, they were remarkably less in number than those of two-rowed barley (Fig. 1). 2. In the aleurone and subaleurone cells of lateral and ventral portions, zigzag modification of the wall as found in barley was could not observed throughout the developing stage. 3. Anticlinal cell walls of nucellar epidermis increased in area about several tens times by expanding of the cell as the endosperm grew fat, and they increased more by folding. A large number of plasmodesmata were formed in the anticlinal cell walls. This may be a proof that the nucellar epidermis developed as the conductive tissue from dorsal vascular bundle to the ventral side (Figs. 2∼10). 4. Wall-ingrowth structure that symbolizes the figure of transfer cell was found in some young dorsal aleurone cells (Fig. 12). However, the transfer cells were small in number in rice, and this differed from two-rowed barley in which many transfer cells were formed in the dorsal portion as reported previously. 5. Dorsal aleurone tissue was composed of 6-8 cell-layers in rice. On the 9-10th day after anthesis, some "unusual cells" were observed sporadically in the young dorsal aleurone tissue. They were stained with toluidine blue darker than ordinary aleurone cells, and were mutually connected with their characteristic uneven cell walls to form a channel across the aleurone tissue (Figs. 13, 14). They degenerated and were depressed gradually in contrast with the normal aleurone cells developed (Figs. 15-17), and that they were found as rather thick traces even in mature aleurone tissue (Fig. 18). The "unusual cells" might be cause of the irregular arrangement of the dorsal aleurone cells. The channels made of connection of the "unusual cells" may play an important role as the translocation pathways through thick aleurone layers which cells were fully packed with aleurone grains etc.
