Studies on the mechanism of the occurrence of hollow root in 'Gensuke'

玄助萝卜因其高品质而在石川县的沙丘地区种植。萝卜在盛夏播种时，常出现根中部纵向中空的“空心根”现象。本研究旨在阐明根空心化发生的机理，当从播种到播种后30天在高温下栽培或用高浓度生长素处理时，这一时期的根生长受到严重抑制，空心根发生率高。以播后60 d根重除以30 d根重的重量增长率大时，空根发生率高，重量增长率小时，空根发生率低。前者根内血管分叉迅速，而后者根内血管间距较小。结果表明，前者的薄壁细胞增殖活跃，促进了根的生长，而后者的薄壁细胞增殖不良，抑制了根的生长，溶生细胞间隙向中空发展，根生长迅速。在适宜的条件下，由于薄壁细胞的不断填充，空间不会发展成空洞，而在不适宜的条件下，由于薄壁细胞的增殖能力差，空间不能被细胞填满，空间发展成空洞，在耐空洞的品种中，薄壁细胞的增殖即使在高温下也不受抑制，结果表明，溶生细胞间隙是否发育成空心根，取决于溶生细胞间隙发育程度与薄壁细胞对间隙的填充程度之间的平衡。

Gensuke daikon has been cultured in the sand dune regions of Ishikawa Prefecture because of its high quality. When the radish is sown in midsummer, "hollow root" which has lengthwise hollow in the central part of the root has been frequently observed. This research was carried out to elucidate the mechanism of the occurrence of hollowness in the root.When Gensuke was cultivated under high temperature or treated with high concentration of auxin from sowing to 30 days after sowing, root growth during that period was severely suppressed with high occurrence of hollow root. The occurrence of hollow root was high when the rate of weight growth by divided the root weight on the 60th day after sowing by that oh 30th day was large, but the occurrence was low when the rate was small. In this cash, vessels in the root bifurcated rapidly in the former, but the space among vessels was small in the latter. This result shows that root growth is accelerated by the active proliferation of parenchymatous cells in the former, but the growth is suppressed by the poor proliferation of the cells in the latter.The lysigenous intercellular space developed to the hollow with rapid root growth. The space would not develop to the hollow under the suitable condition because the space continued to be filled up with parenchymatous cells, but the space developed to the hollow under the unsuitable condition because the space could not be filled up with the cells owing to the poor proliferation of the cells.In cultivars resistant to hollowness the proliferation of parenchymatous cells was not suppressed even under high temperature, hollow root did not occur as the lysigenous intercellular space continued to be filled up with the cells.Summing up these results, whether or not the lysigenous intercellular space develops to hollow is decided by the balance between the degree of development of the lysigenous intercellular space and the degree of the filling of the space by parenchymatous cells.