Role of Hydroxylysine on the Nodulation of Root Nodule Bacteria

Abstract

  The growth of Bradyrhizobium japonicum as well as Rhizobium leguminosarum bv. phaseoli growing in minimal medium was repressed by the addition of hydroxylysine (Hyl), although the sensitivity of the former to Hyl seemed to be lower than that of the latter. The nodulation efficiency of both Glycine max (L.) inoculated with B. japonicum cells and Phaseolus vulgaris (L.) inoculated with R. leguminosarum bv. phaseoli cells was reduced in the presence of Hyl, concomitantly with the decrease in the elongation of roots. Besides, the Hyl contents in the seed (seedling) exudates tended to increase when the host plants were inoculated with an unfavorable strain for their nodulation. These results suggest that the Hyl plays a role in the effective symbiotic relationship by regulating the growth of the root nodule bacteria on the root surface and/or the elongation of the host plant’s roots.