Abstract
Effects of root pruning on the formation and the emergence of crown roots in young rice seedlings were examined. The seedlings at the 3.2 leaf stage after pruning all roots were transplanted to the paddy field. Then serial cross–sections of the main stems of the seedlings at 4.2, 5.2 and 6.2 leaf stages were prepared and observed under a light microscope. The number of the crown root primordia at the 4.2 leaf age increased by pruning the roots. The increase was mainly found in the third ‘unit’ and upward of the stem. At the 5.2 leaf age, the developed roots emerged from the third and fourth ‘units’ and upward of the stem. In addition to the increase in the root number, the stem portion, where the crown root primordia were formed, was extended upward by the pruning. Consequently, the emerged portion of crown roots extended upwardly in the stem. The time of formation and emergence of crown roots was earlier in the root–pruned seedlings than in the intact seedlings. The already–known relationship between the timing of root growth and leaf emergence hither to known in intact seedlings may not be applicable to the root–pruned seedlings.
