Nodulation in clover roots: Correlation with vacuolar pH

Abstract Nodulation patterns of three clover cultivars inoculated with three strains of Rhizobium leguminosarum bv. trifolii were established. Profiles of the frequency of nodule formation in the root-hair zone and no-root-hair zone of Trifolium subterraneum (cvs. Clare and Mount Barker) indicated a more frequent development of nodules in the no-root-hair zone. A different nodulation pattern was observed in Trifolium fragiferum cv. Palestine in which the number of nodules per centimeter did not change along the root.
In order to assess the mechanisms responsible for the different capacity of root tissues to initiate meristematic activity for nodule formation, intracellular pH of the different root zones was measured using ³¹P-NMR spectroscopy. In the two clovers with distinct zones of nodule formation, the vacuolar pH of the no-root-hair zone was 0.3 units higher than that of the root-hair zone, with a lower pH being associated with a lower nodulation frequency.