ESTRUTURA, FISIOLOGIA E NÍVEIS DE ESTRESSE PROMOVIDOS POR GALHAS DE Manihot esculenta (EUPHORBIACEAE) INDUZIDAS POR Iatrophobia brasiliensis (DIPTERA, CECIDOMYIIDAE)

Abstract

The gall-inducing organisms modify the normal growth of plant tissues and organs, through changes in their morphogenic patterns, in search of a structure that offers them shelter, food and protection. The “mosca-da-galha” Iatrophobia brasiliensis induces galls on the leaves of cassava Manihot esculenta. Thus, the aim of the current study is to characterize the anatomy, histochemistry, photosynthesis, immunocytochemistry of the cell wall, levels of oxidative stress and forms of stress dissipation in galls induced by Iatrophobia brasiliensis on Manihot esculenta leaves. So, non-galled leaves and mature galls were collected for analysis. For histological analyses, the samples were fixed, embedded in resin, sectioned in a microtome, stained with toluidine blue and mounted in Entellan©. Fresh samples were used for histolocalization of primary and secondary metabolites. For immunocytochemistry, samples embedded in resin were subjected to monoclonal antibodies for evaluation of pectins, hemicelluloses and proteins of the cell walls. For the physiological analyses, Handy FluorCam– PSI was used to evaluate the chlorophyll a fluorescence in the field, associated with the concentration of chloroplast pigments using an 80% acetone extractor. For the assessment of stress, superoxide anion, hydrogen peroxide and malondialdehyde were quantified, as well as the antioxidant enzymes catalase, non-specific peroxidase, ascorbate peroxidase and superoxide dismutase. M. esculenta galls show tissue compartmentalization rich in primary and secondary metabolites, and a cell wall structured by glycoproteins, pectins, and hemicelluloses. The nutritious tissue was largely labeled by these compounds, which may be related to feed of the galling inducer. The galls of M. esculenta showed a more efficient enzymatic system of antioxidant defense than the leaf, resulting in less stress on the galls, mainly due to the greater activity of POX and SOD. The greater production of hydrogen peroxide, superoxide anion and malondialdehyde in the leaves of M. esculenta generated greater stress, associated with lower activity of the antioxidant system, which seems to have affected the quantum yield of PSII, making it lower than that of the gall. The current study brings news about stress in galls and dissipation pathways, showing greater complexity of these processes when access to the antioxidant system in galls is expanded.