Nitrate reductase (NR) has emerged as a potential NO source in plants. Indeed, the Arabidopsis thaliana NR double-deficient mutant (nia1 nia2) produces low NO and develops abnormal susceptibility to bacterial infection. We have employed quantitative real-time polymerase chain reactions to analyze the effects of NO gas on the expression of defense-related genes in wild-type and nia1 nia2 A. thaliana plants that were inoculated with an avirulent strain of Pseudomonas syringae pv. tomato. The pathogenesis-related gene 1 (PR1) was up-regulated by bacterial infection, and its expression was higher in the wild type than in nia1 nia2. Fumigation with NO attenuated the expression of PR1 and other salicylic acid-related genes in plants that had been inoculated with P. syringae. Nevertheless, NO inhibited the most intense bacterial growth and disease symptoms in nia1 nia2 leaves. The NO fumigation also directly modulated lignin biosynthesis-related gene expression (CAD1) and parts of the auxin (TIR1, ILL1, GH3) and ethylene (ACCS7) pathways, among other defense-related genes, and their modulation was more intense in the NR-deficient mutant. Pathogen inoculation induced delayed but intense H2O2 production in mutant leaves in comparison with the wild type. Hydrogen peroxide potentiated the microbicidal effects of NO against bacterial cultures. These results suggest that NO has a direct microbicidal effect in combination with H2O2 to allow for the attenuation of the SA-mediated defense response, thereby reducing the energy expenditure associated with defense-related gene transcription. Overall, these results highlight the importance of NR-dependent NO production in the establishment of disease resistance.

Trypanosoma cruzi cytosolic (TcCPx) and mitochondrial tryparedoxin peroxidase (TcMPx) play a fundamental role in H(2)O(2) detoxification. Herein, mitochondrial bioenergetics was evaluated in cells that overexpressed TcCPx (CPx) and TcMPx (MPx) and in pTEX. In MPx, a higher expression was observed for TcCPx, and the same correlation was true for CPx. Differences in H(2)O(2) release among the overexpressing cells were detected when the mitochondrial respiratory chain was inhibited using antimycin A or thenoyltrifluoroacetone. MPx had higher O(2) consumption rates than pTEX and CPx, especially in the presence of oligomycin. In all of the cells, the mitochondrial membrane potential and the ATP levels were similar. Because of the mild uncoupling that was observed in MPx, the presence or induction of a proton transporter in the mitochondrial membrane is suggested when TcMPx is expressed at higher levels. Our results show a possible interplay between the cytosolic and mitochondrial antioxidant systems in a trypanosomatid.

Understanding the energy-transduction pathways employed by Trypanosoma cruzi, the etiological agent of Chagas disease, may lead to the identification of new targets for development of a more effective therapy. Herein, the contribution of different substrates for O(2) consumption rates along T. cruzi epimastigotes (Tulahuen 2 and Y strains) growth curve was evaluated. O(2) consumption rates were higher at the late stationary phase not due to an increase on succinate-dehydrogenase activity. Antimycin A and cyanide did not totally inhibit the mitochondrial respiratory chain (MRC). Malonate at 10 or 25 mM was not a potent inhibitor of complex II. Comparing complex II and III, the former appears to be the primary site of H(2)O(2) release. An update on T. cruzi MRC is presented that together with our results bring important data towards the understanding of the parasite's MRC. The findings mainly at the stationary phase could be relevant for epimastigotes transformation into the metacyclic form, and in this sense deserves further attention.

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