The elicitor-induced incorporation of phenylpropanoid derivatives into the cell wall and the secretion of soluble coumarin derivatives (phytoalexins) by parsley (fetroselinum crispum 1.) suspension cultures can be potentiated by pretreatment of the cultures with 2,6-dichloroisonicotinic acid or derivatives of salicylic acid. To investigate this phenomenon further, the cell walls and an extracellular soluble polymer were isolated from control cells or cells treated with an elicitor from fhytophthora megasperma f. sp. glycinea. After alkaline hydrolysis, both fractions from elicited cells showed a greatly increased content of 4-coumaric, ferulic, and 4-hydroxybenzoic acid, as well as 4-hydroxybenzaldehyde and vanillin. Two minor peaks were identified as tyrosol and methoxytyrosol. The pretreatment effect i s most pronounced at a low elicitor concentration. Its specificity was elaborated for coumarin secretion. When the parsley suspension cultures were preincubated for 1 d with 2,6-dichloroisonicotinic, 4-or 5-chlorosalicylic, or 3,sdichlorosalicylic acid, the cells exhibited a greatly increased elicitor response. Pretreatment with isonicotinic, salicylic, acetylsalicylic, or 2,6-dihydroxybenzoic acid was less efficient in enhancing the response, and some other isomers were inactive. This increase in elicitor response was also observed for the above-mentioned monomeric phenolics, which were liberated from cell walls upon alkaline hydrolysis and for "lignin-like" cell wall polymers determined by the thioglycolic acid method. It was shown for S-chlorosalicylic acid that conditioning most likely improves the signal transduction leading to the activation of genes encoding phenylalanine ammonia lyase and 4-coumarate: coenzyme A ligase. The conditioning thus sensitizes the parsley suspension cells to respond to lower elicitor concentrations. I f a similar mechanism were to apply to whole plants treated with 2,6-dichloroisonicotinic acid, a known inducer of systemic acquired resistance, one can hypothesize that fungal pathogens might be recognized more readily and effectively.The interaction of plants with fungal pathogens and the resulting defense reactions of the plant occur initially at single cells and are experimentally difficult to synchronize. For biochemical and physiological studies, therefore, model sys-' Supported by Deutsche Forschungsgemeinschaft and Fonds der * Corresponding author; fax 49-631-205-2998. Chemischen Industrie . 459tems of fungal elicitor preparations and wounded plant tissues or suspension-cultured cells have become customary. Initially, the defense responses studied successfully in this way were mainly the production of soluble fungitoxic "phytoalexins" (Hahlbrock and Scheel, 1989; Bowles, 1990). Subsequently, and with increasing frequency, the elicitor induction of callose deposition (Kauss, 1987(Kauss, , 1990) and the formation of covalently linked cell wall phenolics were also studied (Barber et al., 1989; Bruce and West, 1989; Graham and Graham, 1991). These reactions are generally t...

The disease-resistance response of plant cells is composed of a multitude of biochemical events, and the activation of one of these, the phenylpropanoid metabolism, is pivotal for the survival of cells under stress conditions. The basic features of this facet of the disease-resistance response are beginning to be unraveled in model plant cell culture systems. These studies revealed a novel, alternative pathway for the synthesis of cell wall bound hydroxycinnamoyl esters and lignin. The investigations have, therefore, set the stage for a detailed analysis of the induction process that includes fast, posttranslational activation mechanisms as well as de novo enzyme synthesis. The biosynthesis of phenolic compounds destined for the cell wall is considered to reach far beyond the mere physical strengthening of the cells and includes additional functions, e.g., the release of antimycotic hydroxybenzaldehydes, which are vital for stress compensation. Key words: elicitor-induced phenylpropanoids, cell wall reinforcement, hydroxycinnamoyl esters, lignin, caffeoyl-CoA-specific 3-O-methyltransferase, disease resistance response, parsley (Petroselinum crispum) cell cultures.

Stilbene synthases (STSs) are enzymes that play a critical role in the biosynthesis of stilbene, phytoalexins in a small number of unrelated plant species, and are induced by various biotic and abiotic stressors like pathogen attack, UV-irradiation or ozone exposure. To investigate the molecular basis for ozoneinduced plant stress responses, we have examined the promoter of the grapevine resveratrol synthase (Vstl). In this report we summarize the influence of ozone on gene regulation. In transgenic tobacco a chimeric gene construct, containing the Vstl promoter combined with the fS-glucuronidase (GUS) reporter gene, is rapidly induced by ozone (0.1 lal.1 1, 12 h). The same construct is also strongly induced by ethylene (20 tal-I -t, 12 h). Promoter deletion analysis of the 5' flanking sequence identified a positive regulatory element between -430 bp and -280 bp. This region contains ethylene-responsive enhancer elements, as well ~s an elicitor-responsive sequence in inverse orientation.

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