Correlations between the Lateral Root Formation and the Growth Characteristics of Crown Roots in Rice Plants

The positions of initiation and emergence of lateral roots on crown root axes of rice plants were investigated in relation to the diameter of root tip or the elongation rate of each crown root. 1. The root apex-lateral distance (the distance from the root apex to the most newly emerged lateral root) varied remarkably among various crown roots investigated. However, the distance was found to be closely correlated with the diameter of root tip of each crown root and with its elongation rate. 2. As for the root apex-lateral primordium distance (the distance from the root apex to the position of the youngest lateral root primordium), its relation to the crown root growth varied as the stage of elongation of each crown root advanced. Namely, during the early stage of crown root elongation, the distance exhibited a significant positive correlation with elongation rate of the crown root, but not with the diameter of the root rip. 3. On the contrary, in the later stage of crown root elongation, the distance was found to be closely correlated both with elongation rate of the crown root and with its diameter. Therefore, in the later stage of crown root elongation, the higher the elongation rate and the larger the diameter at root tip, the longer become the root apex-lateral primordium distance and also the root apex-lateral distance. Based on the results mentioned above, it was assumed that the position of initiation and emergence of lateral roots on each crown root axis is in a close relation with elongation rate of the crown roots.