Competence for Elicitation of H2O2 in Hypocotyls of Cucumber Is Induced by Breaching the Cuticle and Is Enhanced by Salicylic Acid

Abstract

Georgia 30602-471 2 (M.G.H.)To study H,O, production, the epidermal surfaces of hypocotyl segments from etiolated seedlings of cucumber (Cucumis safivus L.) were gently abraded. Freshly abraded segments were not constitutively competent for rapid H,O, elicitation. This capacity developed subsequent to abrasion in a time-dependent process that was greatly enhanced in segments exhibiting an acquired resistance to penetration of their epidermal cell walls by Collefofricbum lagenarium, because of root pretreatment of the respective seedlings with 2,6-dichloroisonicotinic acid. When this compound or salicylic acid was applied t o abraded segments, it also greatly enhanced the induction of competence for H,O, elicitation. This process was fully inhibited by 5 PM cycloheximide or 200 PM puromycin, suggesting a requirement for translational protein synthesis. Both a crude elicitor preparation and a partially purified oligoglucan mixture from Pbyfophfbora sojae also induced, in addition t o H,O, production, a refractory state, which explains the transient nature of H,O, elicitation. Taken together, these results suggest that the cucumber hypocotyl epidermis becomes conditioned for competence t o produce H,O, i n response to elicitors by a stimulus resulting from breaching the cuticle and/or cutting segments. This conditioning process is associated with protein synthesis and is greatly enhanced when substances able t o induce systemic acquired resistance are present in the tissue.The interaction of plant cells with potentially pathogenic microorganisms is associated with rather complex biochemical and physiological events. Experiments on these processes are, therefore, often performed with simplified systems in which the pathogen is reduced to "elicitors" and the plant to a mechanically wounded tissue surface or to cell-suspension cultures. These models have already contributed many insights into the mechanisms of plant responses presumably related to defense but still require refinement to better cover the diverse biological features of host/pathogen interactions. It should be considered, for instance, that severa1 signals may act subsequently in the course of pathogenesis and that the nutritional status, age, or a previous infection of a plant can influence the effectiveness of defense responses.

Inhibition of the Plastidic ATP/ADP Transporter Protein Primes Potato Tubers for Augmented Elicitation of Defense Responses and Enhances Their Resistance against Erwinia carotovora

“…Similar to primed parsley (Petroselinum crispum) cells (Kauss and Jeblick, 1995;Katz et al, 1998;Thulke and Conrath, 1998) and primed cucumber (Cucumis sativus; Fauth et al, 1996) and Arabidopsis (Kohler et al, 2002) plants, AATP1(St) antisense tissue also exhibits an increased capacity for both H 2 O 2 production and the activation of defenserelated genes (Figs. 1 and 2).…”

“…However, as indicated by the sd of the given means, these differences in H 2 O 2 production are not statistically significant. It should be mentioned that all tissues tested have been conditioned in water for 4 h before the respective treatment to induce elicitation competency for H 2 O 2 production (for details, see Fauth et al, 1996).…”

“…To quantify the amount of released H 2 O 2 , four tuber discs (3 mm thickness, 1.5 cm in diameter) from respective plant lines were transferred to a petri dish (5 cm in diameter) containing 8 mL of sterilized water and conditioned for 4 h to acquire elicitation competency (Fauth et al, 1996). To prevent anaerobiosis, the discs were incubated on a laboratory shaker at 30 rpm during conditioning.…”

“…Pharmacological studies with diphenylene-iodonium chloride and lanthanum chloride suggest that the augmented H 2 O 2 release in AATP1(St) tissue results from enhanced activation of the plasma membrane-localized NAD(P) H oxidase (data not shown). The 13-amino were conditioned in sterilized water for 4 h to induce elicitation competency (Fauth et al, 1996). The discs were subsequently transferred to fresh petri dishes and incubated in presence of the given compounds.…”

“…H 2 O 2 levels in the supernatant were quantified by ferricyanide-catalyzed oxidation of luminol as described previously (Fauth et al, 1996). Tuber discs to be used for RNA extraction were snap frozen and stored at Ϫ70°C.…”