Modulation of anatomical adaptations of leaves of Avicennia schaueriana (Acanthaceae) by a galling Meunieriella (Cecidomyiidae)

Abstract

Globoid leaf galls with an abaxial concavity are induced by an undescribed species of Meunieriella Kieffer, 1909 (Cecidomyiidae) in Avicennia schaueriana Stapf & Leechm. ex Moldenke (Acanthaceae), a plant extremely adapted to mangroves. The gall-inducers may potentiate anatomical adaptations of host plants for producing a better shelter and food. We expected that some A. schaueriana important adaptations, such as salt glands, were potentiated in galls. Anatomical, histochemical and histometric analyses of non-galled leaves and galls were performed to assess which adaptive features are potentiated in gall development. Epidermis was not significantly altered in adaxial surface, and in the abaxial surface, hypertrophy of epidermal cells seems to compensate the increment in surface area during the gall development. Both the outer and inner gall compartments, separated by a sclerenchyma cap, maintain a dorsiventral arrangement. In such compartments, the proliferated water-storage parenchyma occupies the adaxial layers, followed by a palisade parenchyma, and elongated spongy parenchyma cells. Therefore, dorsiventrality is marked by the differential hyperplasia (predominant in adaxial layers) and cell hypertrophy (predominant in abaxial layers) in galls. Few layers of small nutritive cells are observed in contact to gall chamber, accumulating proteins, lipids, and sugars. The galling Meunieriella sp. can manipulate some adaptations to its own benefit, but A. schaueriana have strong constraints in leaf ontogenesis, possibly due to its specific adaptations to variable salinity and flooding. The proliferated water-storage parenchyma in gall may function as a site of ion accumulation, which could increase the bioaccumulation potential of the organ. The boundaries of host plant plasticity, related to specific environmental constraints, may be determinant in gall anatomical diversity.