Dissolved organic matter (DOM) and effects on the aquatic macrophyte Ceratophyllum demersum in relation to photosynthesis, pigmentpattern and activity of detoxication enzymes

Direct effects of isolated pure humic substances from various German source s on physiological and biochemical functions in the submergend macrophyte C eratophtllum demersum were demonstrated in this study. Environmentally rele vant concentrations of this humic substances in the range of 0.25 - 1.0 mg/ L DOC caused strong negative effects on photosynthesis of C. demersum, and additionally a stress specific change in the chlorophyll pattern of exposed plants. The activity of same detoxication enzymes like the guajacol peroxi dase and the microsomal and soluble glutathione S-transferases were determi ned in relation to exposure to humic substances. It could be demonstrated, that the guajacol peroxidase was strongly elevated and activities of the mi crosomal glutathione S-transferases were decreased by most of the investiga ted humic substances. The soluble glutathione S-transferases seemed not to be affected.