Consequently, galls often reduce the development and performance of their host plants, leading to a reduction in flower, fruit, seed, and biomass production, the main purpose of plant photosynthesis (e.g., McCrea et al., 1985 Sacchi et al., 1988 Fernandes et al., 1993). Changes in source-sink relationships can reduce the photosynthetic capacity in remaining non-galled leaf tissues around the gall developmental sites ( Zangerl et al., 2002 Nabity et al., 2009). The feeding activity of these insects in specific plant tissues (e.g., the phloem) affects the carbon-partitioning mechanisms within the host plant compartments, and alters the balance among source and sink tissues. These sinks drain nutrients from other plant parts ( Mani, 1964 Castro et al., 2012 Huang et al., 2014), which is especially true for galls induced by sucking insects. The detrimental effects of galling insects on the performance of their host plants are linked to the establishment of sinks in gall sites (reviewed by Fernandes, 1987 Fernandes and Santos, 2014). Moreover, a high oxidative stress imposed by the galling herbivores in host plant tissues ( Oliveira et al., 2011) should rupture the homeostasis in gall developmental sites ( Isaias et al., 2015), and demand metabolic reactions, such as the overproduction of phenolic derivatives, and the establishment of a sink of photoassimilates. We take for granted that the integrity of the photochemical and carbon assimilatory apparatus should be maintained in green gall tissues.
Thus, the high oxidative stress in gall developmental sites is dissipated not only by the accumulation of phenolic derivatives in the protoplast, but also of lignins in the walls of neoformed sclereids.Īs a novel approach on the discussion of the impact of galling insects on the photosynthesis of their host plant tissues, we herein address the association of photochemical activity with carboxylation rate in gall tissues. mataybae galls are more susceptible to damage caused by stressors than the non-galled tissues. In addition, the decrease of PSII operating efficiency, ( F’m– F’)/ F’m, and Rfd (instantaneous fluorescence decline ratio in light, to measure tissue vitality) demonstrate that the tissues of B. The low values of maximum quantum efficiency of PSII ( F v/ F m) indicate a low photosynthetic performance in gall tissues. Thus, to supply the demands of gall metabolism, the levels of water-soluble polysaccharides and starch increase in gall tissues. Currently, we assume that the homeostasis in gall tissues is ruptured by the oxidative stress promoted by the galling insect activity.
The contents of sugars and nitrogen were evaluated to quantify the gall sink.
In addition, histochemical tests for hydrogen peroxide and phenolic derivatives were performed to confirm the biotic stress, and set the possible sites where stress dissipation occurs. To access the photosynthesis performance, the distribution of chlorophyllous tissues and the photochemical and carboxylation rates in gall tissues were analyzed. Moreover, the maintenance of low levels of photosynthesis may guarantee O 2 production and CO 2 consumption, as well as may avoid hypoxia and hypercarbia in gall tissues.
Thus, we hypothesize that high levels of nutrients are accumulated during gall development in response to a local maintenance of photosynthesis and to the galling insect activity. This biotic stress is assumed by the histochemical detection of hydrogen peroxide, a reactive oxygen species (ROS), whose production alters gall physiology. The galling insect Bystracoccus mataybae (Eriococcidae) induces green and intralaminar galls on leaflets of Matayba guianensis (Sapindaceae), and promotes a high oxidative stress in host plant tissues. 2Laboratório de Anatomia Vegetal, Departamento de Botânica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Minas Gerais, Brazil.1Laboratório de Anatomia e Desenvolvimento Vegetal, Instituto de Biologia, Universidade Federal de Uberlândia, Minas Gerais, Brazil.