Analysis of Timecourse Changes in Root System Morphology of Rice in Excised Root Culture.

Abstract

The development of cultured seminal root system of rice was analyzed to determine the most appropriate culture period for the characterization of root system morphology. Excised seminal root tips of Taichung Native 1 (TN-1, indica type) and Yukara (japonica type), were cultured for six weeks with the conventional tissue culture method, and their growth was evaluated with developmental, topological and fractal analyses. Developmental root growth parameters, such as the number and length of each root system component, reached almost maximum values at the fourth week in TN-1, and the third week in Yukara. On the other hand, it was possible to characterize the root system morphology by the branching densities of L- and S-type first order lateral roots and the average length of S-type first order lateral roots at the third week. In the timecourse changes of a topological parameter (log a/log μ), which indicates the branching pattern, the difference between cultivars became clear at the third week. The fractal dimension (D), which indicates the complexity of root morphology, was higher in Yukara than in TN-1 throughout the experimental period. This suggested the possibility for characterizing the root system morphology of each cultivar by the D value. Therefore, we concluded that the most appropriate sampling time for the morphological research of cultured seminal root system was three weeks when the conventional excised root culture method is used.