Expression of nodulation genes in Rhizobium and acid sensitivity of nodule formation [review; nitrogen-fixing; leguminous plants; soil acidity]
1989
Richardson, A.E. | Simpson, R.J. (Melbourne Univ., Parkville (Australia). School of Agriculture and Forestry) | Djordjevic, M.A. | Rolfe, B.G. (Australian National Univ., Canberra. Research School of Biological Sciences)
The formation of nitrogen-fixing nodules on roots of leguminous plants by Rhizobium spp. involves a complex interaction between host plant and symbiont. Successful nodulation requires the coordination expression of several nodulation (nod) genes in the bacteria. The expression of these genes is induced by flavonoid compounds present in root exudates of host plants. Growth of Rhizobium spp. and formation of nodules on roots of leguminous plants is known to be adversley affected by low pH and factors associated with soil acidity, but the basis of this acid-sensitivity is poorly understood. Poor induction of nodulation gene expression in Rhizobium is considered to be a major factor contributing to the acid-sensitivity of nodulation formation. Induction of nod gene expression in R. leguminosarum biovar trifolii is markedly reduced in the presence of flavone-inducer at low pH, and is also affected by a net reduction in the concentration of nod gene-inducing factors present in the root exudates of clover seedlings grown in acidic conditions.
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