Abstract
The effects of root pruning on formation of crown root primordia (CRP) in young rice seedlings was examined morphologically in consideration of the size and running of a peripheral cylinder of longitudinal vascular bundles (PV). Seedlings at the 3.2 leaf stage were transplanted to a paddy field after pruning all roots. Main stems were sampled four times until the 7.2 leaf stage; then serial cross-sections were observed under a light microscope. Root pruning decreased the PV area (side area of PV) throughout the stem (from the coleoptile ‘unit’ to the 5th ‘unit’), especially apical part of the stem (from the third ‘unit’ and to apex), but did not affect the CRP number. On the other hand, the diameter of the basal portion of CRP decreased once (4.2 and 5.2 leaf stages) in the third ‘unit’, but it subsequently recovered. Consequently, the number of CRP per PV area and the ratio of the sum of basal area of CRP to PV area were increased by root pruning, especially in the apical part of the stem (from the third ‘unit’ to apex). These results suggested that the number of CRP in young seedlings was unaffected by root pruning at transplantation, although the PV shrank and the CRP diameter decreased temporarily. Moreover, activities of differentiation of CRP and/or formation of the crown root tissues, which originated in PV, seem to be increased by root pruning, promoting recovery from transplantation injury.
