Relationships between the growth direction of primary roots and shoot growth in rice plants.

Abstract

Relationships between the growth direction of primarer roots (Fig. 1) and shoot growth were studied by treating the shoot in various ways for controlling the amount of assimilates translocated from shoot to root system (Table 1). Experiment 1 : With shading and defoliation, the growth of shoot was suppressed and the percentage of horizontally growing primary roots was higher than the control. The removal of tillers, on the other hand, let the growth of the main stem more vigorous and the percentage of primary roots growing obliquely or vertically was higher than the control (Figs. 2 and 3). Experiment 2 : Under high planting density, the growth of shoot was suppressed and the percentage of horizontally growing primary roots was higher than the control. Meanwhile under low planting density, the growth of shoot was more vigorous and the percentage of obliquely or vertically growing primary roots was higher than the control (Table 2, Fig. 4). The growth direction of primary roots is strongly influenced by the shoot growth in each case mentioned above ; i.e. the better growth of shoot increases the proportion of obliquely or vertically growing primary roots, and on the contrary the poor growth of shoot increases the proportion of horizontally growing primary roots. These facts seem to support our assumption that the amount of assimilates translocated from shoot to root system might control the growth direction of primary roots in rice plants.