CONDITIONING OF PARSLEY (PETROSELINUM-CRISPUM L) SUSPENSION CELLS INCREASES ELICITOR-INDUCED INCORPORATION OF CELL-WALL PHENOLICS

The elicitor-induced incorporation of phenylpropanoid derivatives into the cell wall and the secretion of soluble coumarin derivatives (phyt oalexins) by parsley (Petroselinum crispum L.) suspension cultures can be potentiated by pretreatment of the cultures with 2,6-dichloroisoni cotinic acid or derivatives of salicylic acid. To investigate this phe nomenon further, the cell walls and an extracellular soluble polymer w ere isolated from control cells or cells treated with an elicitor from Phytophthora megasperma f. sp. glycinea. After alkaline hydrolysis, b oth fractions from elicited cells showed a greatly increased content o f 4-coumaric, ferulic, and 4-hydroxybenzoic acid, as well as 4-hydroxy benzaldehyde and vanillin. Two minor peaks were identified as tyrosol and methoxytyrosol. The pretreatment effect is most pronounced at a lo w 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 3,5-dic hlorosalicylic 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 respo nse, and some other isomers were inactive. This increase in elicitor r esponse 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 5-chlorosalicylic acid that conditioning mos t 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 cell s to respond to lower elicitor concentrations. If a similar mechanism were to apply to whole plants treated with 2,6-dichloroisonicotinic ac id, a known inducer of systemic acquired resistance, one can hypothesi ze that fungal pathogens might be recognized more readily and effectiv ely.