The influence of colchicin on root nodule formation inTrifolium Pratense

Abstract

Addition of colchicin to nutrient solutions supplied to red clover plants had an inhibitory effect on root development and nodulation. At the lowest colchicin concentrations, a small, non-significant increase in the number of nodules was often observed; in a few experiments a barely significant increase in the number of nodules developing was observed up to concentrations of 10 mg per 1. Colchicin did not influence the growth of Rhizobium and growth of the bacteria in the presence of colchicin (10 mg per 1) had no effect on their subsequent infectivity or ability to fix nitrogen. Treatment with colchicin resulted in the formation of increased numbers of polyploid cells of the clover roots. In addition, it induced the development of deformed root-hairs which probably facilitated infection by Rhizobium and the formation of infection threads. The nodules developing at colchicin concentrations of 10 mg per 1 and higher were small, had an abnormal structure and were ineffective in nitrogen fixation. It is concluded that any stimulatory effect of colchicin on nodulation does not necessarily require to be associated with an increase in the number of polyploid cells in the root cortex. The effect of colchicin can be fully accounted for, initially by the greater number of infections resulting from the development of increased numbers of deformed root hairs, and subsequently by the reduced inhibitory action of the ineffective nodules on the formation of further nodules.