Influence of Salicylic Acid on the Induction of Competence for H2O2 Elicitation (Comparison of Ergosterol with Other Elicitors).

Hypocotyls from etiolated cucumber (Cucumis sativus L.) seedlings were gently abraded at their epidermal surface, and cut segments were used to study the rapid and transient elicitation of H2O2 by ergosterol, chitosan, mastoparan, and a polymeric fungal elicitor. Freshly abraded segments were only barely competent for any H2O2 production, but they developed this competence subsequent to abrasion. This process was enhanced by 2,6-dichloroisonicotinic acid and salicylic acid, which induced acquired resistance to fungal penetration in the epidermal cells. Enhancement of competence induction by salicylic acid was also evident for spontaneous H2O2 production and differed in degree for the various elicitors, indicating that mainly the enzyme complex producing H2O2, but also other components of the elicitation system, improved. Ergosterol, chitosan, and fungal elicitor also rendered the segments refractory to a second stimulation by the same compound, whereas mastoparan was inactive in this respect. The four elicitors also differed markedly in their ability to diminish or enhance H2O2 production by a second treatment with a different elicitor, indicating that several sites of the H2O2 elicitation system are subject to short-term regulation.