No abstract

Selenium (Se) is an essential element for humans and animals that is required for key antioxidant reactions, but can be toxic at high concentrations. We have investigated the effect of Se in the form of selenite on coffee cell suspension cultures over a 12-day period. The antioxidant defence systems were induced in coffee cells grown in the presence of 0.05 and 0.5 mm sodium selenite (Na2SeO3). Lipid peroxidation and alterations in antioxidant enzymes were the main responses observed, including a severe reduction in ascorbate peroxidase activity, even at 0.05 mm sodium selenite. Ten superoxide dismutase (SOD) isoenzymes were detected and the two major Mn-SOD isoenzymes (bands V and VI) responded more to 0.05 mm selenite. SOD band V exhibited a general decrease in activity after 12 h of treatment with 0.05 mm selenite, whereas band VI exhibited the opposite behavior and increased in activity. An extra isoenzyme of glutathione reductase (GR) was induced in the presence of selenite, which confirmed our previous results obtained with Cd and Ni indicating that this GR isoenzyme may have the potential to be a marker for oxidative stress in coffee.

The response of Crotalaria juncea seedlings to nickel (Ni) was investigated. Ni was shown to accumulate mainly in the root system, with little being translocated to the shoots. Catalase (CAT) and glutathione reductase (GR) responses to Ni were also analyzed. CAT activity did not exhibit a clear trend in response to Ni exposure, whereas GR activity appeared to respond to the stress induced by Ni. The results suggest that in C. juncea GR participates in the detoxification of Ni-induced reactive oxygen species via the glutathione-ascorbate cycle.