The inhibitory effects of UV-B radiation (280-315 nm) on Gunnera magellanica growth correlate with increased DNA damage but not with oxidative damage to lipids

Damage to DNA and disruption of membrane integrity by lipid peroxidation processes are two of the proposed causes of UV-B-induced growth inhibition in plants. However, the relative significance of these different types of molecular damage has not been established in experiments carried out under realistic physiological conditions. Plants of Gunnera magellanica (a native herb from southern Patagonia) were exposed to a gradient of biologically effective UV-B doses (from 0 to 6.5 kJ m(-2) d(-1) of UV-B-be) in a greenhouse study. Leaf expansion was measured and sensitive techniques were used to detect damage to DNA (in the form of cyclobutane pyrimidine dimers; CPDs) and lipid peroxidation (via electronic-paramagnetic resonance; EPR). Leaf expansion decreased and the CPD density increased with increasing UV-B doses, but the degree of lipid peroxidation remained unaffected. The highest UV-B dose induced a transient oxidative stress situation (as evaluated using the ratio of ascorbyl radical to ascorbate, A(.)/AH(-)), which was rapidly controlled by an increase in the ascorbate pool. The present results suggest that under a range of UV-B-be doses that overlaps the range of doses that G. magellanica plants experience in their natural environment, growth inhibition is better explained by DNA damage than by increased lipid peroxidation.