CONICET | Buscador de Institutos y Recursos Humanos

External L-proline (Pro) treatment causes cell death in plants. Such damage was suggested to be produced by accumulation of the intermediary toxic metabolite P5C. This compound is generated during both Pro synthesis and catabolism. The first pathway occurs in cytosol and plastids, where delta 1-pyrroline-5-carboxylate (P5C)-synthase (P5CS) reduces Glu to P5C, and P5C-reductase (P5CR) subsequently converts P5C to Pro. The second pathway takes place in mitochondria in two consecutive steps catalyzed by Pro-dehydrogenase (ProDH) and P5C-dehydrogenase (P5CDH) having P5C as intermediate. Recently, the existence of a Pro/P5C cycle involving the activities of ProDH and P5CR has been described in plants. This cycle impedes the accumulation of P5C, but may enhance the reactive oxygen species (ROS) levels. We have recently described that Arabidopsis tissues developing the Hypersensitive Response (HR) activate the catabolism of Pro. These tissues accumulate ProDH transcripts without altering the P5CDH mRNA content. Therefore, increase of P5C or activation of the Pro/P5C cycle may take place in these tissues. To evaluate these possibilities we performed infections in p5cdh mutant plants and quantified the levels of Pro, P5C, Glu and derivatives, in p5cdh- and wild type-infected tissues. In addition, we determined the ROS and cell death levels. We found early and transient reduction of Pro levels in the infected tissues. P5C did not accumulate at this stage both in wild type and in p5cdh infected plants. There was neither a significant change of amino acid levels derived from Glu in these tissues. Furthermore, an increased accumulation of ROS was observed in the leaves of p5cdh mutant compared to wild type plants. Altogether these results suggest that activation of Pro catabolism does not result in P5C increase rather it may induce the Pro/P5C cycle by stimulating the generation of ROS in HR.

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