NODULE-LIKE STRUCTURES INDUCED ON THE ROOTS OF RICE SEEDLINGS BY ADDITION OF THE SYNTHETIC AUXIN 2,4-DICHLOROPHENOXYACETIC ACID

Nodule-like structures were induced on rice varieties Calrose and Peld e using 2,4-dichlorophenoxyacetic acid (2,4-D) in a concentration rang e of 2.5 x 10(-6) M to 1 x 10(-5) M. The nodule-like structures appear ed to result from the fusion of multiple meristems induced in very clo se proximity to each other. The internal tissue differentiation of som e of the nodule-like structures was found to be similar to that of bot h Parasponia nodules and some kinds of determinate legume nodules. The se spheroid nodule-like structures, similar in external morphology to determinate legume nodules, showed no internal infection or colonisati on by Rhizobium strain NGR 234 or the Azorhizobium strain ORS 571. How ever, on the rice variety Calrose, the strain ORS 571 sometimes coloni sed extensively the surface of the nodule-like structures, in comparis on to levels found on emerging lateral roots and to the root surface o f the same plants. The strain NGR 234 did not colonise the surface of the nodule-like structures. The synthetic phytohormone 2,4-D also indu ced a range of other phenomena, including various levels of fusion of primordia and structures with a callus-like surface instead of an epid ermis, but with a differentiated internal anatomy. These experiments i ndicate that tissue development in some types of nodule is the result of a number of meristems fusing together at a single site, and at a ve ry early stage in development.