Prospects of nitrogen fixation in rice

Abstract

Global agriculture relies heavily on fertilizers which are ecologically as well as economically expensive. Nitrogen which is undoubtedly the most important nutrient input required for rice production, is most frequently also a limiting factor. In a world facing acute energy crisis at global level and unpredictable spurs in world crude oil process due to political turmoil's and lack of dependable alternative energy resources, it is imperative to develop the system of rice production which, without compromising on yield out-put, lowers dependability on chemical N-fertilizers besides being ecologically compatible. Nitrogen fixation in rice seems to be an efficient prospective system that is compatible with principles of resource conservation and ecological security. The dream project of BNF rice was started in 1992 based on expert recommendations which involve improving endophytic associations between rice and N2 fixing bacteria, engineering of rice plants capable of forming legume like symbiosis and nodules with rhizobia, transforming rice to ensure expression of nitrogenase and protect nitrogenase system from oxygen damage and enhancing N-use efficiency of rice. A large number of diazotropic microorganisms have been found to be associated with rice roots. Among these endophytic diazotropes, Alcaligenes, Azoarcus, Serratia marcesscens and Azorhizobium caulinodons have received major attention. Though most of the aspects of rice-diazotroph interaction and nitrogen fixation have been elucidated both at genetic as well as molecular level, the engineering of an autonomous nitrogen fixing rice plants is undoubtedly a long term endeavor. A large number of endophytic diazotrophs have been found to be associated with rice and factors encouraging bacterial colonization have been characterized but certain critical differences in rice-rhizobial interaction relative to root nodule symbiosis in legumes have to become a reality. It will require a series of genetic manipulation of nodulation genes from plants and nif genes from bacteria to realize the dream of developing a biologically nitrogen fixing rice. © 2007 Asian Network for Scientific Information.