N2-fixation by endophytic bacteria: questions of entry and operation

Abstract

Endophytic N2-fixing bacteria from several genera can enter plants through natural openings (stomata, hydathodes), natural and artificial wounds (points of emergence of roots, via vegetative propagation techniques) and also intact plant tissues. They may penetrate to xylem vessels or intercellular spaces, but there is no evidence that they can survive in healthy plant cells. The nutrition of endophytic bacteria in these various locations is discussed. It is concluded that subtle interactions between the C and N metabolisms of both host and endophyte may lead to significant N2 fixation without causing undue burdens on the host. There are good prospects for improving these associations by interdisciplinary laboratory and field studies involving both microbiologists and plant scientists.