Studies on the Structure and Physiology of Vegetative Shoot-and Inflorescence Apices in Rice Plants grown on Normal and Degraded Paddy Fields

Abstract

1. The structure and physiology of vegetative shoot-and inflorescence apices in rice plants grown on normal and degraded paddy fields were compared cyto-histologically. 2. The volume of the vegetative shoot apex in the rice plant grown on the degraded paddy field became smaller than that on the normal paddy field from about the middle of July, and this difference in volume was caused by the number of cells which constituted it, and the mitotic activity of the vegetative shoot apex of the degraded paddy field was lower than that of the normal paddy field. 3. The number of tunica layer was fewer and the time of beginning of destruction in the stratification was earlier in the shoot apex in the rice plant grown on the degraded paddy field (Fig. 2). The apex at the transition stage also showed the fewer stratification and, as already shown by Hsu, Sharman and Esau, the apical meristem of the primary branch primordium was gradually organized to the same pattern found in the parent shoot, that was, the apex at the transition stage, initiating the secondary branch primordium which developed in the same manner as itself (Fig. 2, 4). 4. From the general observation on developmental changes of the structure of the shoot apex (Fig. 1), it should be said that the fewer stratification and the earlier destruction of it in the rice plant grown on the degraded paddy field indicate that the shoot apex of it is less vegetative physiologically than that on the normal paddy field. 5. The less vegetative condition and the lower mitotic activity of the apex in the degraded paddy field plot resulted in the earlier transition to the reproductive stage of the vegetative shoot apex, and induced not only the fewer number of vegetative organs-leaf, branch, and spikelet etc., but also the smaller morphology of them (see Table 2, 3. Fig. 3), with the lower grain yield than the normal paddy field plot consequently. 6. Development of the corpus portion was also poor in the shoot apex in the rice plant grown on the degraded paddy field, and the cells of which were of larger size, more vacuolated contents which stained relatively lightly, and the earlier formation of the central lacuna in the internode was observed. 7. The degraded paddy field used in this experiment was a ill drained paddy field, and the soil of the furrow slice of it showed little evidence of active iron compounds and in mid-summer the reduced layer of the furrow slice emited H2S gas remarkably and the attack of Helminthosporium leaf spot occured exceedingly. 8. The apices in rice plants grown on the more typical, well drained degraded paddy field will be investigated with the same method in the near future.