Development of Endosperm Tissue with Special Reference to the Translocation of Reserve Substances in Cereals : II. Modification of cell shape in the developing endosperm parenchyma, aleurone and subaleurone of two-rowed barley

摘要

Developmental processes of the endosperm in two-rowed barley were investigated. Special attention was paid to the peripheral region of endosperm, because the reserve substances were taken into the endosperm through them. Noticeable modifications of cell shape in the endosperm parenchyma, aleurone and subaleurone were found, and they were discussed in relation to taking in or translocation pathway of the reserve substances as ripening advances. During 7th to 12th day after anthesis, especially in 11∼12 day, endosperm parenchyma cells locating at some distance to the periphery showed remarkably irregular modification (Fig. 3). This irregularity was backed to normal as the cells began to store starch grains. The period of modification is the same with the maximum period of the ratio of translocated dry matter to the kernel dry matter in weight (Fig. 1 C). The indented modification was more prominent in the periclinal cell wall than in the anticlinal one. So the area of periclinal boundary between cells increased by 2∼3 times. It seems to be right to consider that the modification has some adaptive function to the translocation from peripheral to inner portion of the endosperm. During 13th to 16th day, the indentation appeared in the cell walls of aleurone (Fig. 4). This period is the rapid increasing stage of reserve substances per day (Fig. 1 B), and nucellar epidermis was in the climax in development. The indentation of aleurone cells may be useful to help the effective acception of reserve substances from nucellar epidermis, then send to inner portion through it. During 17th to 29th day, especially in 17th to 22nd day, subaleurone cells changed their shape to floral-pattern mosaic (Figs. 5, 6 and 7). However they were restored to the normally round shape as they were filled with starch and protein grains (Figs. 8 and 9). This period is in accord with the maximum term of increase of reserve substances per day (Fig. 1 B). Nucellar epidermis already degenerated, and acception pathway of reserve substances had been limitted to the dorsal portion where the transfer cells come near completion of development at this time as reported in the previous paper. In the later stage of ripening, reserve substances accepted might be sent from dorsal portion to the flanks and ventral portion through the subaleurone cells where starch grains are not yet stored. It seems to be adequate to consider that modification of subaleurone cells is an adaptation to the translocation, because the increase of wall area of individual cell by the indentation ranged in 1.6 to 2.1 times, but it is especially high (2∼3 times) in the anticlinal cell walls.