Developmental biology of legume nodulation

SUMMARY Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be tempo...

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Bibliographic Details
Published inThe New phytologist Vol. 122; no. 2; pp. 211 - 237
Main Author Hirsch, A.M
Format Journal Article
LanguageEnglish
Published Oxford, UK Blackwell Publishing Ltd 01.10.1992
Subjects
development
Fabaceae
flavonoids
genetic regulation
induction
lectin
Legume nodulation
literature reviews
modulation
morphogenesis
plant growth substances
Rhizobium
root nodules
symbiosis
development
Rhizobium
Legume nodulation
flavonoids
lectin
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Summary:SUMMARY Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non‐legume hosts, such as rice or maize, increase in number and scope. CONTENTS Summary 211 I. Introduction 211 II. Nodule development 213 III. Nodule initiation 220 IV. The second signal for nodule morphogenesis: role for the plant hormones ? 225 V. Lateral root development 229 VI. Are nodules modified lateral roots ? 229 VII. Conclusions and future prospects 231 Acknowledgements and dedication 232 References 232
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ISSN:0028-646X
1469-8137
DOI:10.1111/j.1469-8137.1992.tb04227.x