Produção de oxido nitrico pela oxido nitrico sintase, nitrato redutase e uma atividade mitocondrial redutora de nitrito na resposta de defesa de Arabidopsis thaliana a Pseudomonas syringae

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The origin of nitric oxide (?NO) in plants has been controversial and nitric oxide synthase (NOS)-like enzyme and nitrate reductase (NR) are claimed as potential sources. However, there is still no direct evidence for ?NO formation from NR during plant-pathogen interactions. Here, we used NR-defective double mutants of Arabidopsis thaliana to investigate the mechanism of ?NO production following infection by an avirulent strain of Pseudomonas syringae pv. maculicola (Psm). Increased formation of L-citrulline from L-arginine was observed in leaf homogenates of both wild-type and nia1 nia2 mutant plants. Electron paramagnetic resonance experiments, however, showed a much higher ?NO production that was dependent on NO2- rather than on L-arginine or NO3- and was also inhibited at high L-arginine concentrations. Inhibition of mitochondrial electron transport abolished and inhibited partially this activity in nia1 nia2 mutants and wild-types, respectively. In situ ?NO production was substantially increased in wild type-plants but not in mutants, following Psm challenge, as measured with the fluorescent probe 4,5-diaminofluorescein diacetate. However, in vivo ·NO production in NR-deficient mutants was visualized only after L-arginine or NO2- infiltration into the leaves. A. thaliana plants defective in NR showed susceptibility to P. syringae that was prevented by infiltration of NO2-. The overall results suggest that NOS, NR, and an important mitochondrial-dependent nitrite-reducing activity cooperate to produce ?NO in amounts enough to prevent Psm dissemination in A. thaliana plants

ASSUNTO(S)

oxido nitrico plantas - defesas fitopatologia

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