On the role of HO in the recovery of grapevine (Vitis vinifera cv. Prosecco) from Flavescence dorée disease.

In the present work, we compared hydrogen peroxide (HO) localisation and the activities/contents of antioxidant enzymes and metabolites in the leaf tissues of grapevine (Vitis vinifera L. cv. Prosecco) plants showing different sanitary status, namely diseased by Flavescence dorée, healthy or recovered. Polymerase chain reaction analysis revealed that the pathogen associated with Flavescence dorée (proposed as 'Candidatus Phytoplasma vitis') was detected in the leaf tissues of symptomatic plants, but was not observed in either the healthy or recovered plants. Hydrogen peroxide accumulated in the phloem plasmalemma of recovered grapevine leaves, but was not detected in either healthy or diseased material. When compared to diseased or healthy plants, recovered plants had distinctly lower extractable levels of catalase and ascorbate peroxidase, two enzymes primarily involved in the scavenging of excess HO generated in different cell compartments. Among healthy, diseased and recovered leaves there was no significant difference in the amount of 2-thiobarbituric acid-reactive substances, which are assumed to reflect the extent of peroxidative breakdown of membrane lipids. Therefore, it is suggested that recovery from Flavescence dorée disease in grapevine might be associated with a long-term, sustained and tissue-specific accumulation of HO in leaves, which reduces numbers or prevents further infection by Flavescence dorée phytoplasma. Recovered grapevine plants might be able to achieve such HO accumulation through a selective and presumably stable downregulation of enzymatic HO scavengers, without altering the levels of other antioxidant systems and without incurring an increased oxidative risk.