Endoperoxides kill malaria parasites via cleavage of their endoperoxide bridge by haem or iron, leading to generation of cytotoxic oxygen-centred radicals. In view of the Leishmania parasites having a relatively compromised anti-oxidant defense and high iron content, this study aims to establish the underlying mechanism(s) accounting for the apoptotic-like death of Leishmania promastigotes by artemisinin, an endoperoxide. The formation of reactive oxygen species was confirmed by flow cytometry and was accompanied by inhibition of mitochondrial complexes I–III and II–III. However, this did not translate into a generation of mitochondrial superoxide or decrease in oxygen consumption, indicating minimal impairment of the electron transport chain. Artemisinin caused depolarization of the mitochondrial membrane along with a substantial depletion of adenosine triphosphatase (ATP), but it was not accompanied by enhancement of ATP hydrolysis. Collectively, the endoperoxide-mediated radical formation by artemisinin in Leishmania promastigotes was the key step for triggering its antileishmanial activity, leading secondarily to mitochondrial dysfunction indicating that endoperoxides represent a promising therapeutic strategy against Leishmania worthy of pharmacological consideration.

The wild species of tomato Solanum pennellii (Lpa) is more tolerant to salt-induced oxidative stress than the cultivated species Solanum lycopersicum (Lem), due to the increase of several antioxidative metabolites and enzymes in this species under stress. The increase of reduced glutathione (GSH), one of these metabolites, in NaCl-treated Lpa, is due at least partly to the elevation of γ-glutamylcysteine synthetase (γ-ECS). Introgression line IL 8–3, which was found to include the Lpa orthologue of the γ-ECS gene (Lpa γ-ECS) in Lem's genetic background, was used to assign this gene to chromosome 8 and to assess its relative contribution to the effective antioxidative response of Lpa to stress. The growth of IL 8–3 and Lem plants responded similarly to NaCl and cadmium (Cd) stresses. In both genotypes, GSH and H2O2 levels responded also similarly to NaCl stress. NaCl and Cd stresses affected similarly the transcription of the γ-ECS gene in leaves of both IL 8–3 and Lpa plants. The effect of buthionine sulfoximine (BSO), a competitive inhibitor of the γ-ECS enzyme, on γ-ECS transcription was also similar in these two genotypes. Taken together, these results suggest that γ-ECS orthologues differ mainly in the regulation of their transcription and not at the post-transcriptional or translational levels. The mutation(s) led to these differences in the response of the two orthologues to the salinity and heavy metal stresses are expected to occur in a cis-regulatory element(s) located relatively close to γ-ECS.

To understand the adaptability to environmental stresses by Deschampsia antarctica, one of the two vascular plants growing in Antarctica, we analysed the activity of several antioxidant enzymes, including peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, EC 1.11.1.6)) and glutathion reductase (GR, EC 1.6.4.2), in shoots subjected to drought stress (PEG-8000, -0.3 MPa). Additionally, levels of total phenolic compounds, flavonoids and ascorbate, were determined. The content of malondialdehyde (MDA), chlorophyll and hydrogen peroxide did not change as a result of PEG-8000 treatment. In addition, treated plants showed higher enzymatic activity of CAT, POD and GR in shoots than control plants. In addition, a high capacity to scavenge free radicals was also detected in stressed plants. These results seem to indicate that in D. antarctica tolerance of drought stress is associated with enhanced activity of antioxidant enzymes and free radical scavenging capacity.