Localization of hydrogen peroxide (H(2)O(2)) and the roles of peroxidases, malondialdehyde, and reduced glutathione in three apple cultivars were compared in healthy trees, trees infected with apple proliferation phytoplasma (APP), and trees that had recovered from the infection. In recovered apple trees, symptoms of the disease and the pathogen had disappeared from the canopy, but phytoplasmas remained in the roots. H(2)O(2) was detected cytochemically by its reaction with cerium chloride to produce electron-dense deposits of cerium perhydroxides.H(2)O(2) occurred in the plasmalemma of the phloem of leaves of recovered apple trees, but not in healthy or APP-infected leaves. In all cultivars, the peroxidase activity detected in tissue from APP-diseased trees was greater than or equal to that of tissue from recovered trees, which equaled or exceeded that of tissue from healthy trees, at two sampling times (May and September). In contrast, the glutathione content of leaves decreased in the reverse order. More malondialdehyde was observed in leaves from recovered trees than in leaves from healthy or APP-infected trees in three of six cultivar-date combinations; in the other three combinations, the malondialdehyde contents of leaves from healthy, infected, and recovered trees were not significantly different from one another. The results suggest that some components of the oxidant-scavenging system in recovered leaves are not very active, leading to an overproduction of H(2)O(2) and, possibly, to a membrane lipid peroxidation.The production of H(2)O(2) appears to be involved in counteracting pathogen virulence.

Hydrogen peroxide (H2O2) localization and roles of peroxidases, malondialdehyde and reduced glutathione\ud were compared in leaves of apricot (Prunus armeniaca) plants: asymptomatic, European Stone Fruits\ud Yellows (ESFY)-symptomatic and recovered. Nested PCR analysis revealed that ‘Candidatus Phytoplasma\ud prunorum’, is present in asymptomatic, symptomatic and recovered apricot trees, confirming previous\ud observations on this species, in which recovery does not seem to be related to the disappearance of\ud phytoplasma from the plant.\ud H2O2 was detected cytochemically by its reaction with cerium chloride, which produces electron-dense\ud deposits of cerium perhydroxides. H2O2 was present in the plasmalemma of the phloem cells of recovered\ud apricot plant leaves, but not in the asymptomatic or symptomatic material. Furthermore, by labelling\ud apricot leaf tissues with diaminobenzidine DAB, no differences were found in the localization of peroxidases.\ud Protein content in asymptomatic, symptomatic and recovered leaves was not significantly different from\ud one another. In contrast, guaiacol peroxidase activity had the following trend: symptomatic\ud > recovered > asymptomatic, whereas reduced glutathione content followed the opposite trend:\ud asymptomatic > recovered > symptomatic. Moreover, no differences were observed in malondialdehyde\ud concentrations between asymptomatic, symptomatic and recovered leaves. The overall results suggest that\ud H2O2 and related metabolites and enzymes appear to be involved in lessening both pathogen virulence and\ud disease symptom expression in ESFY-infected apricot plants

Summary• The main aims of this paper are to investigate: if widespread lichen species ( Xanthoria parietina , Physconia grisea and Physcia adscendens , collected in Italy and Poland) exposed to cadmium (Cd), lead (Pb) and zinc (Zn) synthesize phytochelatins; whether phytochelatins are synthesized by the heterotrophic fungus (mycobiont) or by the photosynthetic alga (photobiont), or by both of the partners; and if there are significant differences in phytochelatin production in the same lichen species growing at different latitudes.• In the lichens investigated, Cd, Pb and Zn induced the biosynthesis of phytochelatins (PC 2 , PC 3 and PC 4 ) and some DES-GLYCIL derivatives. However, only the photobiont partners (the green microalgae of the genus Trebouxia ) were capable of phytochelatin production and, by contrast, aposymbiotically grown mycobionts only produced glutathione.• The Cd-exposed lichens grown in Italy produced significantly larger amounts of phytochelatins than the same species grown in Poland. An opposite trend was observed in Pb-exposed lichens.• The trebouxioid lichens may gain an ecological advantage from their capability to counter heavy metal stress with prompt phytochelatin synthesis.

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The results of several experiments concerning the presence and composition of alkaloids in different tissues (stems, leaves, roots) of Catharanthus roseus L. plants and explants, healthy and infected by clover phyllody phytoplasmas, are reported. The alkaloids extracted and determined by the reverse phase high-pressure liquid chromatography were vindoline, ajmalicine, serpentine, vinblastine, and vincristine. The total alkaloid concentration was higher in infected plants than in the controls, in particular the increase of vinblastine in infected roots was very significant. The ultrastructural observations of infected roots showed alterations of the cell walls and of the nuclei. These results demonstrate that phytoplasmas, detected in all infected tissues by light fluorescence and transmission electron microscopy, play an important role on secondary metabolism of the diseased plants, modifying both the total content of alkaloids and their ratio.