Glyphosate is a broad-spectrum systemic herbicide used worldwide. In susceptible plants, glyphosate affects the shikimate pathway and reduces aromatic amino acid synthesis. Using Arabidopsis seedlings grown in the presence of 20μM glyphosate, we analyzed HO, ascorbate, glutathione (GSH) and protein oxidation content as well as antioxidant catalase, superoxide dismutase (SOD) and ascorbate-glutathione cycle enzyme activity. We also examined the principal NADPH-generating system components, including glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), NADP-malic enzyme (NADP-ME) and NADP-isocitrate dehydrogenase (NADP-ICDH). Glyphosate caused a drastic reduction in growth parameters and an increase in protein oxidation. The herbicide also resulted in an overall increase in GSH content, antioxidant enzyme activity (catalase and all enzymatic components of the ascorbate-glutathione cycle) in addition to the two oxidative phase enzymes, G6PDH and 6PGDH, in the pentose phosphate pathway involved in NADPH generation. In this study, we provide new evidence on the participation of G6PDH and 6PGDH in the response to oxidative stress induced by glyphosate in Arabidopsis, in which peroxisomal enzymes, such as catalase and glycolate oxidase, are positively affected. We suggest that the NADPH provided by the oxidative phase of the pentose phosphate pathway (OxPPP) should serve to maintain glutathione reductase (GR) activity, thus preserving and regenerating the intracellular GSH pool under glyphosate-induced stress. It is particularly remarkable that the 6PGDH activity was unaffected by pro-oxidant and nitrating molecules such as H0, nitric oxide or peroxynitrite.

Arsenic (As) pollution is a major environmental concern due to its worldwide distribution and high toxicity to organisms. The fern Pityrogramma calomelanos is one of the few plant species known to be able to hyperaccumulate As, although the mechanisms involved are largely unknown. This study aimed to investigate the metabolic adjustments involved in the As-tolerance of P. calomelanos. For this purpose, ferns with five to seven fronds were exposed to a series of As concentrations. Young fronds were used for biochemical analysis and metabolite profiling using gas chromatography-mass spectrometry. As treatment increased the total concentration of proteins and soluble phenols, enhanced peroxidase activities, and promoted disturbances in nitrogen and carbon metabolism. The reduction of the glucose pool was one of the striking responses to As. Remarkable changes in amino acids levels were observed in As-treated plants, including those related to biosynthesis of glutathione and phenols, osmoregulation and two photorespiratory intermediates. In addition, increases in polyamines levels and antioxidant enzyme activities were observed. In summary, this study indicates that P. calomelanos tolerates high concentration of As due to its capacity to upregulate biosynthesis of amino acids and antioxidants, without greatly disturbing central carbon metabolism. At extremely high As concentrations, however, this protective mechanism fails to block reactive oxygen species production, leading to lipid peroxidation and leaf necrosis.

No abstract

This study aimed to assess the influence of excess iron on the capacity of accumulation of this heavy metal, mineral composition, and growth of Setaria parviflora and Paspalum urvillei. Seedlings were submitted to 0.009; 1; 2; 4; and 7 mM of Fe-EDTA. In both species there was an increase in the concentration of Fe, Zn, P, and Ca and a decrease in Mn, K, and Mg in the iron plaque. Both species accumulated more iron in roots. In the shoots, S. parviflora showed higher iron content, except at 7 mM. Iron altered the contents of Fe, Cu, K, and Mg in roots, and of Fe, Mn, Zn, N, P, K, Ca, and Mg in shoots. The two species tolerated high iron concentrations and accumulated high content of this element in both shoots and roots. The iron did not reduce their growth. Both species are indicated for studies aiming restoration of iron-contaminated areas.