Effects of selenium content in green parts of plants on the amount of ATP and ascorbate-glutathione cycle enzyme activity at various growth stages of wheat and oilseed rape

The aim of this experiment, conducted under greenhouse conditions, was to assess the influence of various H2SeO3 concentrations added to soil (0.05, 0.15, and 0.45 mM kg-1) on selenium and adenosine triphosphate (ATP) content, and on the activity of the ascorbate-glutathione cycle enzymes in green parts of wheat and oilseed rape. Selenium uptake by the test plants was found to vary, with content increasing from one developmental stage to the next over four stages of the developmental cycle. At the lowest H2SeO3 dose (0.05 mM kg-1), the wheat plants took up much more selenium than did the oilseed rape plants, while the amount of selenium taken up at higher doses (0.15 and 0.45 mM kg-1) was markedly higher in rape. The increasing Se content in the wheat to about 10 mg kg-1 (in the dark) and to about 16 mg kg-1 (in the light) was accompanied by a concurrent increase in the ATP content, which remained unchanged in the light-exposed plants, while clearly decreasing in those kept in the dark. On the other hand, the ATP content of the light-exposed oilseed rape was maintained at a stable level to about 10 mg Se kg-1, following which ATP content was observed to decrease. In contrast, the tendency for the ATP content to decrease appeared immediately in the dark. The increasing plant selenium concentration was accompanied by decreased APX activity in wheat, increased activity in oilseed rape, no major change in the dehydroascorbate reductase (DHAR) activity in oilseed rape and a slight increase in wheat to about 8 mg Se kg-1, followed by a reduction. The glutathione reductase (GR) activity in wheat differed from the activity of DHAR; an increase in the selenium content to about 8 mg kg-1 was accompanied by a distinct reduction, while a significant increase was observed at higher selenium contents; in oilseed rape, the activity was observed to increase slightly within a narrow range of selenium contents (up to 5 mg kg-1), and to decrease thereafter.