TIMECOURSE CHANGES IN 2 DIFFERENT TOPOLOGICAL INDEXES WITH SEMINAL ROOT-SYSTEM DEVELOPMENT OF RICE

For the topological analysis of plant root systems, two sets of topolo gical indices have been proposed; the ratios of measured altitude (a) and total external pathlength (Pe) to the expected value of the respec tive parameter when lateral root branching is assumed to occur randoml y {a/E(a), PelE(Pe)} and to the maximum value of the respective parame ter when all lateral roots emerge from the main root axis (herringbone type) {a/Max(a), Pe/Max (Pe)}. We traced the timecourse changes in th ese indices with root system development of two rice cultivars grown w ith the excised root tip culture method, and evaluated their adaptabil ity for the actual complexity of the branching pattern. The a/E(a) and Pe/E(Pe) did not adequately express the progress of complication with root growth and the difference between cultivars in branching pattern because root system size substantially affected the values. On the ot her hand, changes in a/Max(a) and Pe/Max(Pe) showed close correlation with those in several root developmental characters such as the number and mean branching order of lateral roots (MBO). Thus, we conclude th at a/Max(a) and Pe/Max(Pe) are better indices than a/E(a) and PelE(Pe) for the topological characterization of morphology in the development al study of rice root systems.