Potential and pitfalls of trying to extend symbiotic interactions of nitrogen-fixing organisms to presently non-nodulated plants, such as rice

Abstract

IntroductionPlant-microbe signalling, nodulation, and symbiotic nitrogen fixationThe oxygen paradox and other potential problems related to microbial nitrogen fixation in novel physiological environments Nodulation of cereals: What has been tried, what has been published, and is nodulation really necessary to achieve useful levels of nitrogen fixation Induction of hypertrophies on rice roots and their colonization by microbes Materials and methods Induction and microscopic examination of "nodule-like" structures on rice roots Molecular methods for strain identification Results and discussion Abnormal structures on rice roots grown in China Abnormal structures on rice roots grown at Michigan State University Acknowledgements References AbstractIt has been a long-standing goal in the field of biological nitrogen fixation to extend nitrogen-fixing symbioses to presently non-nodulated cereal plants, such as rice. A number of researchers have recently described the induction of "nodule-like" structures on the roots of cereals primarily by rhizobia, in either the presence or absence of plant cell-wall-degrading enzymes or plant hormones. We briefly review this research and discuss the potential problems associated with the introduction of nitrogen-fixing microbes in novel physiological environments, such as rice roots. The results of experiments carried out in China on the induction of "nodule-like" structures on rice roots by rhizobia are highlighted. In addition, we present preliminary results of a series of experiments designed to repeat and evaluate these results using a variety of microscopic techniques and molecular genetic approaches.

Future benefits from biological nitrogen fixation: An ecological approach to agriculture

“…This topic is discussed in detail by de Bruijn (1995) and it is clear that enormous physiological and biochemical obstacles need to be surmounted before the goal of N2-fixing cereal crops will be realised. The potential benefits of N2-fixing rice varieties, for example, are enormous.…”

The beneficial plant growth-promoting association of Rhizobium leguminosarum bv. trifolii with rice roots

“…The idea that certain rhizobia may intimately colonize rice roots in nature originates from the concept that roots of healthy plants, grown in natural soil, eventually develop a continuum of root-associated microbial colonizations that extend from the rhizosphere to the rhizoplane, and even deeper into the epidermis, cortex, endodermis, and vascular system (Old and Nicolson 1975;Balandreau and Knowles 1978;Old and Nicolson 1978;Klein et al 1990;de Bruijn et al 1995;Stoltzfus et al 1997).…”

Nodulation of groundnut byBradyrhizobium: a simple infection process by crack entry

“…This may aid the study of nodule morphogenesis in newly found symbiotic legume species. Moreover, investigation of the intercellular spreading mode, in being simple and sharing common features with infection processes in some nitrogen‐fixing non‐legumes [17], may yield insights that could provide a framework on how to extend nodulation to agronomically important plant species [18, 19]. However, it must be emphasized that not all non‐legumes are invaded via crack entry, it is not the rule [20].…”