Comparative microscopic and enzymatic characterization of the leaf necrosis induced in Arabidopsis thaliana by lead nitrate and by Xanthomonas campestris pv. campestris after foliar spray

The heavy metal lead was administered to Arabidopsis thaliana plants by foliar spray. At a concentration of l4mol m −3 , the lead nitrate suspension induced densely distributed necrotic lesions on A. thaliana leaves. A number of Arabidopsis ecotypes were tested and a differential response to heavy‐metal toxicity was noted. The necrosis provoked as a result of the phytotoxic effect of lead had a similar appearance to the necrotic lesions observed in a hypersensitive response of A. thaliana to inoculation with Xanthomonas campestris pv. campestris (Lummerzheim et al. 1993, Molecular Plant‐Microbe Interactions 6, 532–544). In addition to this phenotypic resemblance, accumulation of polyphenols and callose depositions observed by microscopic analysis, as well as increases in the activities of the stress‐related proteins β1,3‐glucanases, chitinases and peroxidases, revealed significant similarities in the plant response to the two treatments examined, lead toxicity and bacterial infection. The results allow the establishment of markers for both types of stress.