December
1999
, Volume
12
, Number
12
Pages
1,082
-
1,089
Authors
Samuel
Duodu
,
1
T. V.
Bhuvaneswari
,
1
Thomas J. W.
Stokkermans
,
2
and
N. Kent
Peters
3
Affiliations
1Department of Biology, University of Tromsø, N-9037 Tromsø, Norway; 2Department of Ophthalmology, Case Western Reserve University, Cleveland, OH 44106, U.S.A.; 3Department of Chemistry and Biotechnology, Agricultural University of Norway, N-1432 Ås, Norway
Go to article:
RelatedArticle
Accepted 2 September 1999.
Abstract
Although Bradyrhizobium elkanii is a mutualistic symbiont of legumes, it synthesizes a phytotoxin, rhizobitoxine, that causes chlorosis on a variety of legume hosts, giving a pathogenic character to these interactions. No positive role for rhizobitoxine has been previously demonstrated. Interestingly, rhizobitoxine inhibits the rate-limiting step for ethylene biosynthesis, a plant hormone known to inhibit or down-regulate nodule development. We hypothesized that rhizobitoxine plays a positive role in nodule development through its inhibition of ethylene biosynthesis. To test this hypothesis, host plants of B. elkanii were screened for a differential nodulation response to the wild-type and rhizobitoxine mutant strains. In Vigna radiata (mungbean), the rhizobitoxine mutant strains induced many aborted nodules arrested at all stages of pre-emergent and post-emergent development and formed significantly fewer mature nodules than the wild type. Experiments revealed that nodulation of mungbean plants is sensitive to exogenous ethylene, and that the ethylene inhibitors aminoethoxyvinylglycine and Co2+ were able to partially restore a wild-type nodulation pattern to the rhizobitoxine mutants. This is the first demonstration of a nodulation phenotype of the rhizobitoxine mutants and suggests that rhizobitoxine plays a positive and necessary role in Rhizobium-legume symbiosis through its inhibition of ethylene biosynthesis.
JnArticleKeywords
Page Content
ArticleCopyright
© 1999 The American Phytopathological Society