The effects of sodium chloride-salinity upon growth, nodulation, and root nodule structure of pea (Pisum sativum L.) plants

Pea (Pisum sativum L.) plants inoculated with Rhizobium leguminosarum bv. viciae effective strain 248 were irrigated with nitrogen-free medium supplemented with 0, 25, 50 or 75 mM NaCl. The inhibitory effect of salinity on the growth of pea plants treated with 25 mM NaCl occurred 6 weeks post inoculation. In case of 75 mM NaCl treatment, the same effect was observed 2 weeks post inoculation. In contrast to investigations described in the literature our results clearly indicated that 25 mM NaCl stimulated nodule formation, however, in contrast to control nodules (the medium without NaCl), the nodules were considerably smaller. Remaining variants of salt treatment reduced plant growth, nodulation, and total nodule volume calculated per plant. Microscopic observations showed that salinity: (1) caused the loss of turgor of the nodule peripheral cells, (2) changed nodule zonation, (3) stimulated infection thread enlargement and expansion, (4) caused disturbances in bacterial release from the infection threads, and (5) induced synthesis of electron dense material (EDM) and its deposition in vacuoles. It was also found that cisternae of RER were involved in the formation of special cytoplasmic compartments responsible for synthesis of EDM. Autofluorescence study revealed that salinity increased accumulation of phenolics in pea nodules, as well.