Histopathology and polyphenol content in plants infected by phytoplasmas.

The alterations of cell walls and the localization of several compounds such as polyphenols, suberin, lignin, in plum and apple plants infected with plum leptonecrosis (PLN) and apple proliferation (AP) phytoplasmas respectively, were investigated. Catharanthus roseus plants, infected with AP or PLN were also studied. The 4,6-diamidino-2-phenylindole (DAPI) test and transmission electron microscopy showed the presence of phytoplasmas in all infected plants. Specific histological stainings for cutinized/suberinized cell walls, tannin deposits and vacuolar polyphenol inclusions, performed on leaf and stem tissues, revealed an increase of these substances in infected plum and apple plants. No differences occurred in C. roseus. Total polyphenol analysis confirmed a strong increase (3-fold) in the polyphenol content in infected tissues, particularly in plum leaves. From the data obtained it appears that polyphenols can be considered as defence-related metabolites in plum and apple plants infected by phytoplasmas. Further investigations are necessary to determine whether these compounds play a specific role in the development of all phytoplasma/host interactions and in the defence-related processes.