Effects of Singlet Oxygen Generated by the Nematicidal Compound ɑ-Terthienyl from Tagetes on the Nematode Aphelenchus a Venae

Aphelenchus avenae was rapidly killed by photoactivated ɑ-terthienyl generating singlet oxygen upon irradiation with near ultraviolet light under aerobic but not under anaerobic conditions. Thus molecular oxygen is necessary for nematicidal effects of the activated compound. Glucose-6-phosphate dehydrogenase and acetylcholinesterase from homogenates of A. avenae were inhibited by the photoactivated compound in the presence of air. The singlet oxygen quenchers serum albumin, histidine, methionine, tryptophan and azide protected the enzymes against photo-activated ɑ-terthienyl in air-saturated solutions. Acetylcholinesterase was much more resistant than glucose-6-phosphate dehydrogenase to singlet oxygen because higher light intensities and longer exposure to near ultraviolet light was needed for complete inactivation. Possibilities of the photosensitizer as pesticide are discussed briefly.