Recovery in Apple Trees Infected with the Apple Proliferation Phytoplasma: An Ultrastructural and Biochemical Study

Abstract

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.

cDNA-AFLP analysis of gene expression changes in apple trees induced by phytoplasma infection during compatible interaction

“…At the present, little is known about the genes involved in the phytoplasma-plant host interaction that can lead to production of defence proteins, increase of phenolic compounds and hydrogen peroxide overproduction in host plants (Musetti et al 2000(Musetti et al , 2004Junqueira et al 2004). The host gene expression in Catharanthus roseus after challenge with three different mollicutes, 'Ca.…”

HflB Gene-Based Phytopathogenic Classification of ‘Candidatus Phytoplasma mali’ Strains and Evidence that Strain Composition Determines Virulence in Multiply Infected Apple Trees

“…Ultrastructural, cytochemical, and gene expression analyses of phloem of healthy, visibly diseased, and recovered apple trees revealed various differences. Recovered trees are characterized by the presence of hydrogen peroxide (H 2 O 2 ), callose and phloem protein accumulation, and the upregulation of genes involved in synthesis of callose and phloem protein (Musetti et al 2004(Musetti et al , 2010). …”

Quantitative X‐ray microanalysis of hydrogen peroxide within plant cells

“…To address the role of H 2 O 2 in stress responses, it is not only important to study its subcellular localization but also to investigate changes in its concentration in the different compartments. Histochemical techniques have been widely used for the detection of H 2 O 2 generated in plant cells during plant-pathogen interactions (Alvarez et al, 1998;Bestwick et al, 1997;Bozsó et al, 2005;Iwano et al, 2002;Melillo et al, 2006;Musetti et al, 2004Musetti et al, , 2005Renard-Merlier et al, 2007;Soylu et al, 2005;Thordal-Christensen et al, 1997;Waetzig et al, 1999), in response to wounding (Le-Deunff et al, 2004;Orozco-Cá rdenas and Ryan, 1999;Orozco-Cá rdenas et al, 2001), salinity (Herná ndez et al, 2001;Menezes-Benavente et al, 2004;Wi et al, 2006a), gamma irradiation (Wi et al, 2006b(Wi et al, , 2007, water stress (Hu et al, 2006), ozone stress (Pellinen et al, 1999(Pellinen et al, , 2002, and plant growth regulators, e.g., abscisic acid, jasmonic acid, salicylic acid, and ethylene precursor (Bóka et al, 2007;De Cnodder et al, 2005;Hu et al, 2005). The cytochemical dye 3,3-diaminobenzidine (DAB) or alternatively, the more sensitive CeCl 3 , have been used to assess the subcellular localization of H 2 O 2 .…”