Expressão dos genes nod de Rhizobium tropici, R. etli e R. leguminosarum bv. phaseoli e estabelecimento da nodulação do feijoeiro na presença de exsudatos de sementes de Mimosa flocculosa e Leucaena leucocephala

Expression of nod genes in Rhizobium tropici, R. etli, R. leguminosarum bv. phaseoli and bean nodulation in the presence of Mimosa flocculosa and Leucaena leucocephala seed exudates

SEÇÃO III - BIOLOGIA DO SOLO

Expressão dos genes nod de Rhizobium tropici, R. etli e R. leguminosarum bv. phaseoli e estabelecimento da nodulação do feijoeiro na presença de exsudatos de sementes de Mimosa flocculosa e Leucaena leucocephala(¹)

Expression of nod genes in Rhizobium tropici, R. etli, R. leguminosarum bv. phaseoli and bean nodulation in the presence of Mimosa flocculosa and Leucaena leucocephala seed exudates

F. M. Mercante^I; A. A. Franco^II

^IPesquisador da Embrapa Agropecuária Oeste, BR 163, Km 253, Caixa Postal 661, CEP 79804-970 Dourados (MS). E-mail: [e-mail]

^IIPesquisador da Embrapa Agrobiologia. Km 47, Ant. Rodovia Rio-São Paulo, CEP 23851-970 Seropédica (RJ). E-mail: [e-mail]

RESUMO

Na etapa inicial da troca de sinais moleculares entre macro e microssimbiontes, a interação do feijoeiro e estirpes de Rhizobium tropici, R. etli e R. leguminosarum bv. phaseoli foi avaliada pela expressão dos genes nod de estirpes bacterianas, contendo a fusão nodA::gusA. Esta avaliação foi efetuada por meio da atividade da enzima ß-glucuronidase, utilizando, como indutores, exsudatos liberados pelas sementes de Mimosa flocculosa e Leucaena leucocephala. Além disso, avaliou-se o efeito da adição desses exsudatos no estabelecimento da nodulação do feijoeiro, cv. Carioca. Nos testes "in vitro", a mistura de exsudatos de sementes de feijoeiro e M. flocculosa promoveu aumentos sinergísticos significativos na expressão dos genes nod, tanto das estirpes de R. tropici (CIAT 899/pGUS 32 e F 98.5/pGUS 32) quanto de R. etli (CFN 42/pGUS 32). Em condições controladas, a adição dos exsudatos, tanto de M. flocculosa quanto de L. leucocephala, proporcionou aumento significativo na nodulação inicial do feijoeiro, quando foi inoculada a estirpe CFN 42 (R. etli). A nodulação do feijoeiro cultivado em vasos com solo não foi inibida pelo suprimento de N-mineral, quando se inoculou a estirpe CIAT 899 (R. tropici) e foram fornecidos exsudatos de sementes de M. flocculosa.

Termos de indexação: Phaseolus vulgaris, genes nod, ß-glucuronidase, simbiose, sinais moleculares.

SUMMARY

The first steps of molecular signal exchange between the bean plant and its Rhizobium spp. microsymbionts were studied. The effects on nodulation of the addition of seed exudates of two different leguminous tree plants, Mimosa flocculosa or Leucaena leucocephala, in the presence of R. tropici, R. etli or R. leguminosarum bv. phaseoli were studied. The expression of nod genes was also measured "in vitro" by the activity of ß-glucuronidase on different genetically modified strains possessing the fusion nodA::gusA, using as inducers seed exudates from both leguminous trees. In general, a very complex interaction among the different inducers was observed. Seed exudates, both from Mimosa and Leucaena, led to a significant raise on initial nodulation of the bean plant when inoculated with the strain of R. etli CFN 42 but not when inoculated with R. tropici or R. leguminosarum bv. phaseoli. Mixed beans and Mimosa seed exudates presented a sinergistic effect on the expression of nod genes, measured by the activity of ß-glucuronidase, on strains of R. tropici (CIAT 899/pGUS 32, F 98.5/pGUS 32) and R. etli (CFN 42/pGUS 32). The addition of nitrogen did decrease common bean nodulation except when the plants were inoculated with the strain CIAT 899 (R. tropici) and supplied with seed exsudates from M. flocculosa.

Index terms:Phaseolus vulgaris, nod genes, molecular signals, ß-glucuronidase, symbiosis.

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Recebido para publicação em fevereiro de 1999

Aprovado em abril de 2000

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(1

) Parte da Tese de Doutorado, apresentada pelo primeiro autor à Universidade Federal Rural do Rio de Janeiro - UFRRJ.

Datas de Publicação

• Publicação nesta coleção
  06 Out 2014
• Data do Fascículo
  Jun 2000

Histórico

• Aceito
  Abr 2000
• Recebido
  Fev 1999