The role of lipid and non-lipid components of Phytophthora infestans in the elicitation of the hypersensitive response in potato tuber tissue

The hypersensitive reaction of potato tuber tissue, measured by necrosis and phytoalexin accumulation, was elicited by lipids and lipid-containing and lipid-free fractions extracted from mycelium of Phytophthora infestans. The most active fraction extracted after homogenization in phosphate buffer was composed of carbohydrate, protein and lipid. A heat-released preparation containing very low levels of eicosapentaenoic, arachidonic and dihomo-γ-linolenic acids was more active than a lipid extract of the mycelium. The majority of the elicitor of the mycelium remained associated with the wall residue after extraction.

No relation was found between the activity of the fractions and their content of specific fatty acid elicitors. The activity of most fractions could not be explained by synergism between the eliciting fatty acids and mycelial carbohydrate. Furthermore, the activity of the lipid fractions appeared to be attenuated by some fungal component. Many of the fractions were shown by analytical isoelectric focussing to contain carbohydrate and protein bands also present in an elicitor obtained from culture filtrates of P. infestans. It is suggested that both lipid and non-lipid materials in the mycelium of P. infestans are able to elicit the hypersensitive response in potato tuber tissue.