Plants that cannot fix nitrogen rely on a symbiotic relationship with bacteria. Legumes release flavonoids that attract bacteria; subsequently, bacteria release lipochitooligosaccharides called Nod factors that induce plant root cell deformation. Finally, the bacteria become trapped in nodules protruding from the roots. Recent advances in understanding the process of nodule formation have prompted Cárdenas et al. to review these findings. Nod factors are responsible for causing root cell depolarization and concomitant fluctuations in intracellular ionic concentrations. A large part of the review is devoted to Ca2+ fluxes that occur intra- and extracellularly. The authors also discuss the unclear temporal hierarchy of Ca2+ influx and G protein activation, as well as the work that will be required for elucidating Nod action.
Cárdenas, L., Holdaway-Clarke, T.L., Sánchez, F., Quinto, C., Feijó, J.A., Kunkel, J.G., and Hepler, P.K. (2000) Ion changes in legume root hairs responding to Nod factors. Plant Physiol. 123: 443-452. [Full Text]