SURFACE NADH PEROXIDASES AND OXYLIPIN PATHWAY ARE INVOLVED IN THE RECOVERY FROM PHYTOPLASMA DISEASE IN APPLE.

Phytoplasmas are prokaryotic plant pathogens responsible for deterioration of several trees. In apple tree, the proliferation of the disease, caused by phytoplasmas, may undergo a spontaneous disappearance of symptoms, which are associated to hydrogen peroxide production in the phloem, a phenomenon called recovery. The aim of this work was to identify the biochemical pattern associated to the recovery by examining some enzymatic activities and metabolites in leaves from healthy, diseased and recovered plants. NAD(P)H oxidase/peroxidase, lipoxygenase, hydroperoxide lyase and phenylalanine ammonia lyase (PAL) activities were assayed. All these activities, except for PAL, were increased in leaves from recovered plants. Salicylate and jasmonate content was also determined, showing that the increase in recovered leaves was ascribed to jasmonate only. These results suggest that the activation of surface/plasma membrane redox systems is crucial in promoting the recovery process in apple tree, which then proceeds through the oxylipin pathway, leading to jasmonate. Conversely, salicylic acid appears to be involved only in the response to disease, but not in the subsequent recovery