Galling insects as phenotype manipulators of cell wall composition during the development of galls induced on leaves of Aspidosperma tomentosum (Apocynaceae)

Abstract

The gall structure is built from redifferentiation of host plant tissues, changing the cell wall proprieties and associated functions. Because of the oxidative stress imposed by the galling insect on the plant tissues, some phenotypic traits associated with cell wall metabolism may be suppressed during gall development. Using an immunocytochemical approach we investigated the pectin and glycoprotein composition of the cell walls during non-galled leaf development and galls induced on Aspidosperma tomentosum (Apocynaceae). Embedding in historesin was used for anatomical characterization, as well as for immunocytochemical analyses. The samples were probed with the primary monoclonal antibodies JIM5, JIM7, LM1, LM2, LM5 and LM6. The gall develops especially from cell hypertrophy and hyperplasia of the spongy and palisade parenchyma, which determine its shape. Epitopes of β-D-galactan and α-L-arabinan in the galls were totally suppressed or less expressed. The increased labeling of homogalacturonan epitopes, especially in senescent galls, is a clear indicator that pectin methylesterase activity is maintained despite oxidative stresses imposed by the galling insect. Arabinogalactan proteins were not detected in any non-galled leaf or gall stages. The galling insect deeply changed the structure and deposition pattern of the cell wall, promoting new functionalities in the gall tissue compartments.