Histo-Cytological Researches on Translocation and Ripening in Rice Ovary : I. Histological changes and transfer pathways in the developing ovary

Abstract

Developing process of rice ovary, var. Koshihikari, was observed with microscope by semi-thin sections, prepared through double fixations of glutaraldehyde and osmium tetroxide and embedded in Spurr's resin. 1. The accumulation of starch grains made rapid progress in the endosperm during 8-22 days after flowering, and the accumulation almost finished in each part, the centre in 15 days, the side in 15-20 days, the ventral side in 20 days, the lateral sides in 20-25 days and the lateral-dorsal sides in 25-30 days after flowering successively. 2. The vascular bundle fell into deformation about 30 days after flowering. 3. In the epidermal cells of the and lateral sides, dense cytoplasm, numerous small vacuoles and fibrous structure (arrows) were observed 6 days after flowering, and subsequently the cytoplasm became dilute or transparent but nucleus and osmiophilic globules on and after 7-10 days. The epidermis degenerated 20 days after flowering in the ventral side, 25 days in the lateral sides and 30 days in the side successively. The developing aspects in the epidermis, as mentioned above, are thought to correspond closely with the accumulating process of starch grains in the endosperm. 4. The nucellus inside the epidermis was compressed to a thin layer 5 days after flowering, however, the degeneration in the side continued till 20-25 days and survived four or five layers of the projection. As the cell walls of the degenerated nucellus are stained purple-blue with toluidine blue O, the walls may easily let solutes pass through. 5. About the time when the proaleurone cells ceased to proliferate 7 days after flowering, started off the accumulation of lipid and the formation of aleurone vacuoles, and the globoids could be found about 14 days after flowering. The aleurone cells had thick walls with no wall-ingrowth, however, stained purple-blue with toluidine blue O. 6. The increase of cell number in the endosperm reached to the end 7 or 8 days after flowering, and as seen in Figs. 6 and 9, each cell of the endosperm had foamy vacuoles and a nucleus in the centre. Thereafter, the foamy structure of vacuoles disappeared as increase of starch grains. 7. It is supposed that, after migrating from the sieve elements of vascular bundle to the projection, solutes transfer to the endosperm by two pathways. One is dorsal pathway on which the solutes straightly transfer from projection into endosperm, and the other is nucellar epidermis pathway on which the solutes transfer into endosperm via epidermis.