Redifferentiation of leaflet tissues during midrib gall development in Copaifera langsdorffii (Fabaceae)

AbstractThe tree Copaifera langsdorffii is a superhost for galling herbivores. This plant species has great morphogenetic potential, and responds differently to the stimuli of more than 20 gall-inducing insects. Among these, an undescribed species of Cecidomyiidae induces a midrib gall in which a radial cecidogenetic field is generated and the leaflet tissues redifferentiate. Our objectives were to assess the amplitude of this cecidogenetic field, in which the leaflet tissues were influenced by the feeding action of the cecidomyiid; how the final gall shape was generated; and if tissue redifferentiation conferred any adaptive value on the galling herbivore. Leaflet morphogenesis followed the pattern described in the literature for simple leaves, resulting in a mesophytic arrangement. Tissue redifferentiation due to gall formation revealed that in a midrib gall, abaxial epidermal cells divided to enlarge the gall; spongy parenchyma cells originated the storage tissue, secretory structures, and vascular bundles; palisade parenchyma cells became homogeneous; and adaxial epidermis originated the nutritive tissue. Cell elongation, a necessary step towards cell redifferentiation, is triggered by an increase in water transport to the gall site and vacuole pressure due to neoformed xylem bundles. The generation of the final shape of the midrib gall involved repetitive histological steps in response to the amplitude of the cecidogenetic field. The largest impact of the cecidomyiid feeding action occurred in gall tissues redifferentiated from protoderm and adaxial ground meristem, which provided advantages to the gall maker of the C. langsdorffii midrib gall in terms of nutritional value, microenvironment, and protection against natural enemies

Structure of Insect Galls on Two Sympatric Subspecies of Chrysothamnus nauseosus (Pall. Ex Pursh) Britton (Asteraceae)

Foi estudada a estrutura de oito galhas causadas por insetos em duas subespécies simpátricas, Chrysotamnus nauseosus subsp. consimilis e C. nallseosus subsp. hololeucus (Asteraceae). Neste sistema, 3 galhas são específicas para uma das subespécies, 3 para a outra e 2 são comuns a ambas as subespécies. As galhas são causadas por Cecidomyiidae e Tephritidae, ocorrendo no ápice caulinar, nas gemas axilares, nos nós e entrenós das plantas hospedeiras. Tricomas, estruturas secretoras e esclerênquima foram observados em várias das galhas estudadas e podem representar estratégias protetoras e/ou defensivas contra os inimigos naturais do galhador. Sete das galhas estudadas apresentaram tecido nutritivo, cujas células podem ser semelhantes às meristemáticas ou então mostrar características de células parenquimáticas. Tecido nutritivo não ocorreu na única galha de ambrosia. A análise de galhas desenvolvidas em plantas filogeneticamente relacionadas possibilitou concluir que as respostas cecidogênicas estão sob influência da ação específica do parasita e são direcionadas pelo estágio de diferenciação da célula vegetal no momento da indução

Source–sink relationship and photosynthesis in the horn-shaped gall and its host plant Copaifera langsdorffii Desf. (Fabaceae)

AbstractThe horn-shaped gall of Copaifera langsdorffii is induced by an unidentified species of Diptera: Cecidomyiidae and stands out among the other gall morphotypes by its bizarre shape and high infestation level over the years. Its role as a sink of photoassimilates in comparison to the non-galled leaflets was assessed through the quantification of nitrogen, carbohydrates, pigment content and the apparent relative electron transport rate (ETR) during different developmental stages. The levels of nitrogen and starch decrease in galls as leaflets mature. Total soluble sugars and the water-soluble polysaccharide concentration were higher in galls, whereas, chlorophyll content and ETR values were higher in leaflets rather than in galls. However, the latter presented significantly higher concentrations of total carotenoids. The low nitrogen and chlorophyll contents are related to the low photosynthetic activity, indicating that the CO2 assimilation in galls is insufficient to fully supply their metabolism, reinforcing it as a sink of photoassimilates. The amount of sugars allocated to the gall tissues corroborates this hypothesis, and is probably used as energy supply for both gall structure maintenance and herbivore nutrition. The reduced intercellular spaces on the horn-shaped gall structure imply little gas exchange and, thus, hypoxic conditions on the gall tissues. However, the incipient photosynthesis might be important to provide oxygen to the structure and avoid hypoxia, enabling gall metabolism