Factors Affecting the Elicitation of Sesquiterpenoid Phytoalexin Accumulation by Eicosapentaenoic and Arachidonic Acids in Potato

Abstract

Eicosapentaenoic and arachidonic acids in extracts of Phytophthora infestans mycelium were identified as the most active elicitors of sesquiterpenoid phytoalexin accumulation in potato tuber slices. These fatty acids were found free or esterified in all fractions with elicitor activity including cell wall preparations. Yeast lipase released a major portion of eicosapentaenoic and arachidonic acids from lyophilized mycelium. Concentration response curves comparing the elicitor activity of the polyunsaturated fatty acids to a cell-free sonicate of P. infestans mycelium indicated that the elicitor activity of the sonicated mycelium exceeded that which would be obtained by the amount of eicosapentaenoic and arachidonic acids (free and esterified) present in the mycelium. Upon acid hydrolysis of lyophlized mycelium, elicitor activity was obtained only from the fatty acid fraction. However, the fatty acids accounted for only 21% of the activity of the unhydrolyzed mycelium and the residue did not enhance their activity. Centrifugation of the hydrolysate, obtained from lyophilized mycelium treated with 2 N NaOH, 1 molarity NaBH4 at 100°C, yielded a supernatant fraction with little or no elicitor activity. Addition of this material to the fatty acids restored the activity to that which was present in the unhydrolyzed mycelium. The results indicate that the elicitor activity of the unsaturated fatty acids is enhanced by heat and base-stable factors in the mycelium.patible races of the fungus. The responses are characterized by electrolyte leakage, necrosis, and the accumulation of antimicrobial sesquiterpenes (7,10,23,29).Recently, we reported the polyunsaturated fatty acids, all-cis-5,8,11,14,17-eicosapentaenoic and all-cis-5,8, 11,14-eicosatetraenoic (arachidonic) acids, as the simplest and most active elicitors of sesquiterpenoid phytoalexins found in extracts of P. infestans (4,5). This was the first report of these fatty acids eliciting responses associated with plant hypersensitivity and of the occurrence of eicosapentaenoic acid in the Pythiaceae. Others had tentatively identified arachidonic acid in Pythium debaryanum and P. infestans and it has been found in numerous other Phycomycetes (31). Gellerman and Schlenk (14) identified eicosapentaenoic acid as the predominant fatty acid in Saprolegnia parasitica. Our findings were a significant departure from those of other studies of fungal elicitors which attributed activity to polysaccharides and glycoproteins obtained from fungal culture filtrates or mycelial cell walls (1).In this paper, we present further details concerning the elicitor activity of eicosapentaenoic and arachidonic acids and evidence for other factors in mycelial extracts of P. infestans which dramatically enhance fatty acid elicitor activity. In addition, we report that cell wall preparations contain small amounts of these fatty acids and only a small proportion of the total elicitor activity present in the mycelium of P. infestans. MATERIALS AND METHODSElicitors are metabolites produced ...

Transient Induction of Phenylalanine Ammonia-Lyase and 4-Coumarate: CoA Ligase mRNAs in Potato Leaves Infected with Virulent or Avirulent Races of Phytophthora infestans

“…Induced lignification was associated with the non-host resistance response ofpotato tubers to Cladosporium cucumerinum (12). Oligoglucan fragments (22), lipophilic substances, particularly arachidonic acid (2), and a glycoprotein isolated from Pi culture filtrate (15) have been described as active elicitors of sesquiterpenoid phytoalexin synthesis and/or hypersensitive browning.…”

Involvement of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in the Regulation of Sesquiterpenoid Phytoalexin Synthesis in Potato

“…Elicitors are substances which can trigger the accumulation of phytoalexins in plants in the absence of an attacking microorganism (27). Arachidonic and eicosapentaneoic acids are natural components of the lipids from Phytophthora infestans, a pathogen of potato (Solanum tuberosum), and each elicits the accumulation of SSM3 when applied to the cut surface of potato tubers (4,5,10). Many of the SSM are phytoalexins and accumulation of these fungitoxic sesquiterpenes is correlated with disease resistance in potato (17,18).…”

Les phytoalexines et leur intervention dans la résistance hypersensible aux champignons phytopathogènes

“…Elles sont, en général, absentes des plantes saines' (Keen, 1971;Darvill et (Kuc, 1976;Lisker et Kuc, 1977; Hargreaves et Bailey, 1978;Stoessl, 1980; Bostock et al, 1982;Yoshikawa, 1983;Darvill et Albersheim, 1984;De Wit, 1986;Ward, 1986 (Bailey, 1983) (Strange, 1987;Rouxel, 1988). Ils sont aussi particulière-ment intéressants pour comparer les capacités intrinsèques de production de différents cultivars sans tenir compte du parasite (Rouxel, 1988).…”