Estrutura e metabolismo de galhas foliares induzidas por Hemiptera (Psyllidae) em Pouteria ramiflora (Mart). Radlk. (Sapotaceae)

Abstract

Cap. 1 - Galling insects manipulate host plant tissues towards its adaptive success. However, depending on insect’s taxa and feeding habits, gall structure may have different levels of tissue complexity. In general, sucking insects induce structurally simple gall, and consequently, few histochemical changes are also observed. Ceropsylla sp. (Hemiptera) induce intralaminar galls on leaves of Pouteria ramiflora (Sapotaceae) and we hypothesized that this gall followed the simple structural and histochemical patterns proposed for sucking insects. Gall development occurs by processes of cell hypertrophy and hyperplasia from cells of chlorophyllous leaf tissue to form gall cortex. This cortex can be spatially divided into adaxial and abaxial, where there is neoformation of vascular bundles. In the abaxial gall cortex of gall there ir intense lignification on both sides of nimphal chamber. Although structurally simple, gall tissue form a centrifugal gradient of reducing sugars, and starch granules were detected around the vascular bundles. In addition, centrifugal gradients of phenolics, auxins and ROS (reactive oxygen species) were observed in the adaxial cortex. These molecules are associated with the processes of cell elongation as observed in the gall cortex. Furthermore, the presence of phenolic compounds, proanthocyanidins, and lignified tissue, are important in the control of oxidative burst in gall tissues. Cap. 2 - The processes of gall induction and establishment induces high oxidative stress in the host plant tissues. This stress is the initial trigger for a series of structural and functional transformations in gall tissues. In addition, the impact promoted by galling insect alters the photosynthetic rates, leading the gall tissues to develop different mechanisms of energy dissipation. Cerospsylla sp. (Hemiptera: Psyllidae) induces structurally simple galls on leaves of Pouteria ramiflora (Mart.) Radlk. (Sapotaceae) that with a complex histochemical gradient and a pronounced area of chlorophyll tissue. Gall formation alters the photosynthetic performance and energy dissipation, but the photosynthetic capacity is maintained. The accumulation of phenolic compounds and intense cell wall lignification in gall tissue configure an efficient oxidative stress scavenging system, and consequently redox imbalance adjustment in gall tissues. Once maintained, photosynthesis contributes to oxygen diffusion in galled tissues and capture of carbon dioxide, avoiding hypoxia and hypercarbia. The dynamics between these processes are fundamental to the establishment of the host plant – gall interaction.