Element distribution in faba bean root nodules under salinity and its effects on growth, nodulation and nitrogen fixation

Faba bean cv. Giza 3 was grown in hydroponic cultures and inoculated with R hizobium leguminosarum bv. viceae TAL 1402. Salinity levels at 40, 80 and 1 20 mM NaCl were applied at transplanting and inoculation. The highest level of salinity level (120 mM) significantly suppressed nodulation, nitrogenas e activity and plant growth. This salinity level also significantly decreas ed the concentrations of macro and micro nutrients in faba bean leaves. X-r ay microanalyses of nodules under high levels of NaCl indicate that Ca, K, Mg and S were lower in the infected and uninfected cells of faba bean nodul es than control ones, whereas, Na and Cl were higher. Nitrogen content of n odules was significantly higher in plants treated with high salinity levels than nonsalinized ones. However, the N content of shoots was lower than th e controls, The inhibition of nitrogenase activity at high levels of salt s tress could be explained in terms of product inhibition of the enzyme as an efficient feedback regulation mechanism, The X-ray microanalysis results r evealed that the N export from nitrogen-fixing cells is sensitive to salini ty and is controlled by element distribution in nodules.