OBPC Symposium: Maize 2004 & beyond—Intracellular colonization of cereals and other crop plants by nitrogen-fixing bacteria for reduced inputs of synthetic nitrogen fertilizers

Abstract

The problem of environmental nitrogen enrichment is most likely to be solved by reducing the inputs of synthetic nitrogen fertilizers through the creation of cereals that, like legumes, are able to fix nitrogen. In legumes, rhizobia present intracellularly in vesicles in the cytoplasm of nodule cells fix nitrogen endosymbiotically. Rhizobia within these membrane-bounded compartments are supplied with energy from plant photosynthates and, in return, the bacteria provide the plant with biologically fixed nitrogen. Recently, we have demonstrated, using novel inoculation conditions with very low numbers of bacteria, that cells of the root meristems of maize, rice, wheat, and other major non-legume crops can be colonized intracellularly by the non-rhizobial, non-nodulating, nitrogen-fixing bacterium, Gluconacetobacter diazotrophicus, that occurs naturally in sugarcane. G. diazotrophicus expressing nitrogen-fixing genes is present in membrane-bounded compartments in the cytoplasm of cells of the root meristems of the target cereals and non-legume species, similar to the intracellular colonization of legume root nodule cells by rhizobia. In order to obtain an indication of the likelihood of adequate growth and yield of maize, for example, with reduced inputs of synthetic nitrogen fertilizers, we are determining the extent to which nitrogen fixation is correlated with systemic intracellular colonization by G. diazotrophicus, with minimal or zero inputs of synthetic nitrogen fertilizer.