Long-term exposure to enhanced ultraviolet-B radiation in the sub-arctic does not cause oxidative stress in Vaccinium myrtillus

The aim of this work was to assess whether or not oxidative stress had deve loped in a dwarf shrub bilberry (Vaccinium myrtillus L.) under long-term ex posure to enhanced levels of ultraviolet-B (u.v.-B) radiation. The bilberry plants were exposed to increased u.v.-B representing a 15 %, stratospheric ozone depletion for seven full growing seasons (1991-1997) at Abisko, Swed ish Lapland (68 degrees N). The oxidative stress was assessed on leaves and stems by analysing ascorbate and glutathione concentrations, and activitie s of the closely related enzymes ascorbate peroxidase (EC 1.11.1.11) and gl utathione reductase (EC 1.6.4.2). The affects of autumnal leaf senescence a nd stem cold hardening on these variables were also considered. The results showed that the treatment caused scarcely any response in the studied vari ables, indicating that u.v.-B flux representing a 15 % ozone depletion unde r clear sky conditions is not sufficient to cause oxidative stress in the b ilberry. It is suggested that no strain was evoked since adaptation was pos sible under such u.v.-B increases. The studied variables did, however, resp ond significantly to leaf senescence and especially to stem cold hardening.