Inhibition of Apoplastic and Symplastic Peroxidase Activity from Norway Spruce by the Photooxidant Hydroxymethyl Hydroperoxide.

Young, clonal Norway spruce trees (Picea abies L.) were exposed for 2 years at high altitudes to ambient atmospheric concentrations of photooxidants containing hydroxymethyl hydroperoxide (HMHP) as an important constituent. In spruce needles from a site with higher concentrations of organic peroxides in air, the apoplastic peroxidase activities were significantly lower than in needles exposed to lower organic peroxide concentrations. Guaiacol peroxidase activities in total needle extracts were not affected. In vitro HMHP at a concentration of 35 [mu]M inhibited apoplastic and total needle guaiacol peroxidase activities by 50% at pH 5.25. At the same pH, ascorbate-specific peroxidase activity required about 100 [mu]M HMHP for 50% inhibition. At pH 7, 1.46 mM HMHP caused a 50% reduction in guaiacol peroxidase and a 13% reduction in ascorbate peroxidase activity. The present results suggest that HMHP in ambient air may affect peroxidase activity in spruce needles. Peroxidases located in the relatively acidic aqueous phase of the cell walls appear to be more susceptible to HMHP inhibition than those present in neutral or slightly alkaline symplastic compartments of cells such as the cytosol or chloroplasts.

Detection of atmospheric OH radicals.

The detection of atmospheric OH radicals by laser long path absorption spectroscopy is described. This technique is specific to OH and easily calibrated. In various field measurements from below the detection limit (5*10(5)/cm3) up to 8.7*10(6) OH radicals/cm3 have been observed. Measurements of meteorologic parameters and mixing ratios of other trace gases simultaneously with OH allow comparison of observed OH levels with reaction kinetic model calculations.