EFFECTS OF BORON ON RHIZOBIUM-LEGUME CELL-SURFACE INTERACTIONS AND NODULE DEVELOPMENT

Boron (B) is an essential micronutrient for the development of nitroge n-fixing root nodules in pea (Pisum sativum). By using monoclonal anti bodies that recognize specific glycoconjugate components implicated in legume root-nodule development, we investigated the effects of low B on the formation of infection threads and the colonization of pea nodu les by Rhizobium leguminosarum by viciae. In B-deficient nodules the p roportion of infected host cells was much lower than in nodules from p lants supplied with normal quantities of B. Moreover, the host cells o ften developed enlarged and abnormally shaped infection threads that f requently burst, releasing bacteria into damaged host cells. There was also an overproduction of plant matrix material in which the rhizobia l cells were embedded during their progression through the infection t hread. Furthermore, in a series of in vitro binding studies, we demons trated that the presence of B can change the affinity with which the b acterial cell surface interacts with the peribacteroid membrane glycoc alyx relative to its interaction with intercellular plant matrix glyco protein. From these observations we suggest that B plays an important role in mediating cell-surface interactions that lead to endocytosis o f rhizobia by host cells and hence to the correct establishment of the symbiosis between pea and Rhizobium.