Influence of SO2and NO2Exposure on Glutathione, Superoxide Dismutase and Glutathione Reductase Activities in Scots Pine Needles

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Abstract
A 50-year-old Pinus sylvestris L. stand was exposed for 2 years to low concentrations of SO2 and NO2 in an open-air exposure experiment in northern Sweden. The mean SO2 concentrations in the centre of the exposed plot during the 1988 exposure from 14 June to 25 September, and during the 1989 exposure from 6 June to 30 September were 15 nl 1−1 and 12 nl 1−1, respectively. The corresponding values for NO2 were 15 nl 1−1 and 10 nl 1−1, respectively. The concentration in the control plot was never higher than a few ppb, and mostly below 1 nl 1−1. Needles sampled from the SO2 and NO2-exposed area showed reduced activities of glutathione reductase (GR; EC 1.6.4.2) and superoxide dismutase (SOD; EC 1.15.1.1) compared with controls. The GR activity showed decreased levels in autumn and winter, while the exposure had ceased, and SOD showed decreased activity during the second summer of exposure. Neither membrane-bound nor water-soluble anti-oxidants such as α-tocopherol, carotenoids or glutathione changed due to the exposure. The sulphur/nitrogen ratio was increased in needles that were exposed to SO2 and NO2 implying a changed nutrition balance. The results suggest that the capacity of SOD and GR in the ascorbate-glutathione pathway was reduced due to the exposure to air pollutants.

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