Factors Influencing the Development of Rice Crown Roots Grown with "Leaf Cutting" Method

Abstract

Isolated "shoot units" each composed of one leaf, one internode and crown roots were cultured using "leaf cutting" method under different conditions in order to investigate the factors influencing the root diameter and elongation. Roots cultured under the leaf-lightened condition marked high elongation rate up to 4-5 cm/day. Root elongation continued for more than 50 days and diameter of their newly elongated parts gradually decreased. Dark treatment as well as defoliation quickly reduced both elongation rate and diameter of roots. Apical parts of roots which continued to elongate for relatively long period became as thin as 200 μm in diameter, but those of roots which stopped quickly were relatively thick (400-500 μm). In shoot units cultured in 0.5-3.0% glucose solution, their roots were thickened and elongated at a high rate (3-4cm/day) even in dark. On the other hand, mannose was severely inhibitory to root development. Ammonium, nitrate or auxins at certain concentrations reduced the elongation of root but they did not have any positive effect on the diameter. Kinetin increased the diameter of roots, but reduced their elongation rate. The results seem to show: 1) among the tested substances, sugar proved to be the most important for root development and 2) for elongation of a root with a certain size of diameter, enough quantity of sugar supply corresponding to its diameter is indispensable.