Nod factor enhances calcium uptake by soybean

Inoculation with rhizobia or application of Nod factors (lipo-chitooligosaccharides, LCOs) causes transient increases in cytosolic calcium concentration in root hairs of legume plants. We conducted experiments to evaluate whether application of LCO and inoculation with rhizobia improved 45CaCl2 uptake into soybean (Glycine max [L.] Merr.) leaves. Roots of soybean seedlings with one developing trifoliolate were immersed in Murashige and Skoog (MS) basal liquid medium containing treatment solutions and 45CaCl2, and the plants were incubated under continuous light. After 24 h, leaf samples were taken, and their radioactivity levels were determined. Addition of NodBj-V (C18:1 MeFuc) at a concentration of 10–7 M increased 45Ca2+ uptake. Inoculation with genistein-induced Bradyrhizobium japonicum strain 532C and USDA3 also increased 45Ca2+ uptake; whereas, inoculation with strain Bj-168, a nodC-mutant incapable of producing LCO, did not. Rhizobia that do not normally nodulate soybean, i.e. Rhizobium leguminosarum, and Sinorhizobium meliloti did not affect calcium uptake, nor did the tetramer or pentamer of chitosan, or lumichrome. Surprisingly, Rhizobium sp. NGR234, which can nodulate some types of soybean, although without effective N2-fixation, also did not affect calcium uptake. This work suggests that the rhizobial symbiosis, in addition to its known role in provision of nitrogen fixation, also improves early calcium uptake into soybean plants.