Studies on the Root Hair "Curling Factor" of Rhizobium

A crude preparation of an extracellular polysaccharide (EPS) produced by Rhizobium spp. was obtained by alcohol precipitation from the supernatant fraction of centrifuged cell suspensions. This material induced curling and deformation of clover (Trifolium fragiferum) root hairs in a manner characteristic of that previously shown to be induced by rhizobia and cell-free filtrates. The extent of deformation was proportional to the concentration of the crude polysaccharide in the plant growth medium. Extracellular polysaccharide from a noninfective strain of R. trifolii differed chemically from that produced by a related infective strain and induced only a slight deformation of clover root hairs. Cell-free EPS from infective R. trifolii did not induce the formation of infection threads in clover root hairs inoculated with noninfective cells of R. trifolii. The possible relation between this crude root hair "curling factor" and the postulated "pectic enzyme inducer" implicated in the infection process is discussed.