Recovery of development and functionality of nodules and plant growth in salt-stressed Pisum sativum - Rhizobium leguminosarum symbiosis by boron and calcium

Nodules developed in Pisum sativum L. cv. Argona inoculated with Rhizobium leguminosarum bv. viciae 3841 and growing under saline conditions (75 mmol/L NaCl) are non functional and had abnormal structure. The infected cells contained a low amount of endophytic bacteria, compared to treatments without salt. Addition of B (up to 55.8 μmol/L) and Ca2+ (up to 2.72 mmol/L) increased bacterial population of host plant cells in salt-stressed nodules. Furthermore, symbiosomes developed inside the nodules from salt treated plants presented a degraded peribacteroid membrane. This effect was also prevented by combined addition of B and Ca2+. Given the importance of both nutrients in cell wall structure, the pectin fraction was studied by electron microscopy and immunological methods. Salt stress produced cells with walls dramatically altered or even degraded in several zones. Pectin polysaccharides, detected by JIM 5 monoclonal antibody, increased in cells under salinity. These effects resembled typical effects of B-deficiency reactions in cell walls, and the increase of both Ca2+ and especially B also prevented these alterations.