Studies on Starch Contained in the Tissues of Rice Plant : IX. Distribution of starch near the shoot and root apices.

Abstract

Using several varieties of japonica rice, the auther observed the distribution of polysaccharides or starches near the shoot apex and the root tip under the microscope. The sections cut by paraffin method were stained chiefly by Schiff's reagent. The results are summarized as follows: 1. Normally two parts, 2-layered tunica and corpus can be recognized in the vegetative shoot apex. No polysaccharide granule can be found in the parts where the cells have much proteins and dividing activity; that is tunica, outermost layer of corpus, and leaf primordia just after differentiation. However, in later when the primordia of 1st order panicle branches cease to differntiate and shoot apex does not grow any more with only one tunica layer, small granules of polysaccharide appear even in the tunica and outermost corpus layer. In the vegetative shoot apex, cells in the 4th layer, that is the 2nd layer of corpus, begin to contain minute polysaccharide, and thereafter the cells of corpus located inwards and downwards contain gradually larger granules. It is suggested that sugars translocated from the leaves reach to the shoot apex, being consumed immediately by the active cell division without remaining any stock-polysaccharide, but that in the older cells which are relatively weak in cell division, sugars are stored as polysaccharides for a while. These polysaccharide or starch grains become larger as the cells become older and larger until the cells grow very rapidly into large ones consuming almost all starch contained there. 2. The axis is continuous from the corpus, but the differentiation of nodes and internodes are not clearly observed before the insertion of leaf-3 in which a band of starch begins to be recognized. Transitory starch grains are abanduntly stored in the nodal regions being larger as the nodes become older. At the VII node, the nodal plate grows into stellate parenchyma and the stored starch disappears, thereafter it does not store starch. Starch is also found in the internodes, but its amount is less than that in the nodal plate, especially in the central part which becomes lacuna later on. The cells in the VI-VII internode elongates so rapidly, consuming stored starch probably, that there can not be found any starch in the internode just after the completion of lacuna formation. However, the internodes gradually restore large compound starch grains soon which are dissolved and translocated to the other parts, especially to panicle, during the ripening period. 3. The base of young leaves also contain starch. The older the leaves become, the larger the starch in the size, and the largest starch can be seen in the base of 5th leaf. The starch in the 6th leaf base abruptly disappears, and this is probably due to the consumption caused by the rapid elongation of the cells. In this stage the leaf elongation almost ceases, adcompanying lacuna formation, and then the leaf-sheath restores much starch grains till they are translocated to the other parts, especially to panicle. 4. It is an interesting fact that the 6th leaf sheath, VI-VII internode, and VII node elongate very rapidly almost simultaneously accompanying tiller elongation and rooting from the VII node, and the temporarily stored starch in the above tissues disappears abruptly with their rapid elongation. 5. Root cap always contains much falling starch, but meristems of root tip scarecely have polysaccharide granules except the regions which Dr. Clowes called "Quiescent Center". In general, relatively great size of starch grains exist in the young metaxylem cells, and smaller ones in the cortex parenchyma, but in either case starch disappears with the rapid elongation of these cells, and thereafter they do not restore starch any more. But in the cases when much starches are forced to be stored in the tissues of shoot, restored starch can be seen in the cortex parenchyma in the base of each matured root. 6. [the rest omitted]