A persistent meristem is formed in nodular structures elicited by Nod factor or by a Rhizobium meliloti exopolysaccharide mutant in alfalfa plants which nodulate spontaneously.

摘要

Certain alfalfa (Medicago sativa) plants are able to nodulate spontaneously (Nar character) and form well-developed, elongated nodules in the absence of Rhizobium. Nar+ and Nar- plants were selected and selfed, producing S1 populations with either ahigh or a very low frequency of Nar+ plants, respectively. To assess the influence of the Nar character on nodule development, studies were conducted to determine whether Nar+ and Nar- progenies treated with the Rhizobium meliloti Nod factor or inoculated with a R. meliloti exopolysaccharide mutant differed in terms of nodule meristematic activity. Following addition of the Nod factor NodRmIV(Ac, S, C16:2), only small nodular outgrowths were formed on Nar- progenies, whereas an increased number of elongated nodules was observed on Nar+ progenies. Nodules induced by a R. meliloti exo- mutant on Nar- progenies lacked a persistent meristem and arrested in development soon after emergence, whereas on Nar+ progenies they possessed a persistent meristem andelongated. From both experiments, it is concluded that in Nar+ plants, the capacity to induce the persistent meristem observed during spontaneous nodulation is conserved in nodules elicited by Nod factors or exo- mutants.