Description: The effects of three different initial degrees of infection (30, 45 and 70 percentage) of the green alga Scenedesmus incrassatulus with the unicellular fungal parasite Phlyctidium scenedesmi on cell growth, protein, polypeptide and isoenzyme profiles of both SOD and CAT in the host cells were investigated. The effects of the strong oxidant sanosil with algicide and fungicide action and pathogen invasion were compared. Protein amount decreased significantly under the influence of parasite invasion. Sanosil diminished drastically the polypeptide content. Trace protein and polypeptide amounts were present in zoospores of Phlyctidium. Two intensive new polypeptides were detected in the profile of zoospores. Phlyctidium increased CAT activity in the host cells especially in the case of the highest parasite initial infection. Sanosil enhanced CAT activity similarly to parasite invasion. In contrast, SOD activity decreased drastically after treatment with the highest parasite concentration. A new highly active isoenzyme (Rm 0.26) appeared in the profile of invaded Scenedesmus cells originated from Phlyctidium genome. The data concerning the changes of protein, polypeptide and isoenzyme profiles of the antioxidant enzymes CAT and SOD due to the parasite infection and oxidant treatment were discussed as a proof that parasite invasion acted at the molecular level causing oxidative stress

Remarks: Proceedings of the XI National Conference on Plant Physiology, 18-19 november 2009, Sofia, Bulgaria