Factors responsible for the curling and branching of clover root hairs by Rhizobium

Summary The branching of clover root hairs was due to a factor (or factors) readily extracted from cells of Rhizobium trifolii and found in seedling solution supporting clover roots inoculated with this organism. Part of the active material was retained within a dialysis sac but a smaller, escaping fraction evoked the same response. The branching fraction was stable at 100°C and, partly, to nuclease and periodate, but was unstable when left in contact with the cells and when treated with trypsin. The dried residue of active filtrate contained 2% nucleic acid, 20% protein and about 34% carbohydrate which included antigenic lipopolysaccharide (approximately 1.6%). The branching response could not be attributed to either of these polysaccharides or to indole acetic acid. The capacity to cause branching was absent from all non-invasive mutants, but was increased in ineffective invasive forms, compared with the effective parent strain.Moderate curling was quantitatively much less striking and was generally found in the same preparations as showed branching. Notable exceptions were the lack of significant moderate curling in the filtered inoculated seedling solution and retention of this capacity in avirulent mutants.Marked curling occurred only when viable virulent rhizobia were present. Avirulent mutants were incapable of causing marked curling but the response to ineffective variants was rather better than to their effective parent strains. A dialysis membrane separating bacteria and plant roots prevented marked curling. re]19750214