Studies on the Ripening of Wheat Grain : 5. Formation of pericarp, seed coat and hyaline layer.

Abstract

The processes of formation of pericarp from ovary wall, seed coat from integument and hyaline layer from nucellus were investigated morphologically. Observations were made on abdominal and flank surfaces of three portions such as the basal (near the embryo), central and near the top of the kernel respectively. Development of the furrow side tissue was not studied in this report. The ovary wall, integument and nucellus did not develop until the completion of the fertilization in the embryo sac. Therefore, the development of these tissues presumably pocesses a close relationship with the fertilization. In general, the growth of the covering tissues of the kernel to the longitudinal direction was carried out by cell division and subsequent cell elongation, while, the growth to the transverse direction was dependent mainly on the cell enlargement rather than increase in cell number. The enlargement of the cells started from basal portion and the rate of enlargement was higher at base than that of the top except in nucellar epidermis. Maturation of the cells began with basal tissue. Duration of the development of tissues was classified into 4 intervals: Not later than the 10th day after anthesis, division of all tissues ceased, and outer integument and nucellar tissue except its epidermis entirely had been degenerated. The enlargement of the cells was occurred in the span of the next 10 days, and during the 20th to 30th day, the changes of cell walls and cell contents took place, and pericarp, seed coat and hyaline layer reached to the morphologically complete structure. Within the last 10 days, the tissues shirinked with the drying of the endosperm. As compared with the development of endosperm, it can be said that the development of the covering tissues proceeded faster than that of the former. The resistance and its gradient to entry of water into the kernel from the outer surface of the covering tissue was observed from the 11th day after anthesis, and it corresponded to the begining of cuticula formation in the inner integument whih becoms seed coat later.