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 b y foliar spray. At a concentration of 14mol m(-3), the lead nitrate su spension induced densely distributed necrotic lesions on A. thaliana l eaves. 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. thali ana to inoculation with Xanthomonas campestris pv. campestris (Lummerz heim 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 i ncreases in the activities of the stress-related proteins beta-1,3-glu canases, chitinases and peroxidases, revealed significant similarities in the plant response to the two treatments examined, lead toxicity a nd bacterial infection, The results allow the establishment of markers for both types of stress.