Oxidative biodegradation of tetrachloroethene in needles of Norway spruce (Picea abies L.)

Through employing [14C]-PER exposure experiments it was shown for the first time that PER taken up by drought-stressed spruce needles via the air/needle pathway is preferably degraded to trichloroacetic acid (TCA) in the chloroplasts. TCA formed by oxidative biotransformation is mineralised to CO2 and HCl via various degradation routes. HCl contributes to increased proton concentration in the chloroplast, inducing a pH shift leading to a pathophysiological effect on H+ transport from the thylakoid interior into the stroma. As a result of their high degree of dissociation and related protonation, the PER metabolites, TCA and HCl, cause a change in protein structures. In addition to this, the TCA anions created in the process may lead to destabilisation of the thylakoid membrane potential. The damage to the chloroplasts inflicted by protons and trichloroacetate ions subsequently leads to an impairment of photosynthesis, most particularly to uncoupling of photosynthetic electron transport. Since progressive aridity as consequence of the climate change observed throughout the world is predicted, a regionally variable marked enhancement of the phytotoxic risk caused by PER emission is anticipated.