Evidence for a Biogenic Amine Pathway in the Plant-parasitic Nematode Oitylenchus dipsaci

A number of studies have reported the presence of dopamine in free-living and animal-parasitic nematodes (6), but, to our knowledge, Aphelenchus avenae is the only plant-parasitic nematode in which this neurotransmitter has been shown by direct assay of tissue homogenates (7). This paper presents experimental evidence of the existence of biochemical pathways leading to the production of dopamine in Ditylenchus dipsaci, thus suggesting that dopamine is a ubiqui tous n e u r o t r a n s m i t t e r in a wide range of economically important plantparasitic nematodes. Preparation of nematode homogenates: Ditylenchus dipsaci was cultured on alfalfa callus tissues grown on nutrient agar at 21 C following Krusberg's procedure (3). The nematodes were harvested from 6-8-weekold cultures by a modified Baermann funnel technique under sterile conditions at 25 C for 2 days. The collected nematodes were then concentrated by centrifugation at 8,000 g for 5 minutes and washed twice with distilled water before homogenization. Water-packed nematodes (ca. 2.5 ml) were suspended in 5 ml phosphate buffer pH 6.8 and homogenized in a glass tissue grinder with the aid of glass powder for 30 minutes in an ice bath. The homogenate was centrifuged at 15,000 g for 15 minutes at 0 C. The supernatant served as the crude nematode extract and was used immediately. Incubation of reaction mixture: The procedures for radiolabelling the reaction