Caracterização anatômica, química e ultraestrutural de espinhos secretores em duas espécies de Opuntioideae (Cactaceae).
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Data
2019-02-28
Autores
Silva, Stefany Cristina de Melo
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Universidade Estadual Paulista (Unesp)
Resumo
Nectários extraflorais (NEFs) são comuns e morfologicamente diversos em Cactaceae, podendo se apresentar como espinhos altamente modificados ou não, folhas escamiformes e regiões epidérmicas e corticais especializadas na base ou ao redor das aréolas. Contudo, pouco é conhecido sobre a natureza dos NEFs em cactos e, mesmo, há dúvidas se o exsudato pode ser qualificado como néctar. Nosso objetivo foi analisar a morfologia, anatomia e ultraestrutura dos espinhos secretores em Brasiliopuntia brasiliensis e Nopalea cochenillifera e a composição química da secreção. Espinhos secretores foram processados para análises aos microscópios de luz (campo claro e confocal) e eletrônicos de varredura e transmissão (convencional e citoquímica). A composição dos açúcares e de aminoácidos foi analisada por cromatografia líquida de alta performance (HPLC). Observações de campo mostraram que o exsudato acumulado no ápice dos espinhos é removido por formigas. Os aspectos ontogenéticos, estruturais e funcionais dos espinhos secretores se mostraram semelhantes nas duas espécies estudadas. Os espinhos secretores se originam a partir do meristema areolar, tendo início como pequenas protuberâncias formadas por protoderme e meristema fundamental. Espinhos na fase secretora apresentaram a) base dilatada preenchida por células pequenas com paredes pecto-celulósicas delgadas, citoplasma denso e núcleo volumoso; b) região mediana alongada composta por células fibriformes com paredes não-lignificadas; e c) porção apical afilada com células fusiformes com paredes não-lignificadas. Tecidos vasculares estão presentes na região basal dos espinhos. Ultraestruturalmente, as células da região basal apresentaram contorno irregular e parede com plasmodesmos amplos; a lamela média é intumescida nos ângulos entre as células; no citoplasma ocorrem mitocôndrias, retículo endoplasmático rugoso, poliribossomos, plastídios e dictiossomos abundantes. Análises citoquímicas permitiram identificar a origem dictiossomal das vesículas encontradas no citoplasma dessas células e o mecanismo de liberação da secreção via exocitose. As análises químicas indicaram que o exsudato liberado pelos espinhos secretores é rico em açúcares; em ambas as espécies o exsudato se mostrou sacarose-dominante e com perfil de aminoácidos similar. Nossos resultados indicam a ocorrência de intensa síntese de substâncias hidrofílicas confirmando que tais espinhos são nectários extraflorais.
Extrafloral nectaries (EFNs) are common and morphologically diverse in Cactaceae, and may be highly modified spines or not, scamiform leaves and specialized epidermal and cortical regions located at the base or around the areoles. However, little is known about the nature of EFNs in cacti, and even if the exudate can be qualified as nectar. We aimed to analyze the morphology, anatomy and ultrastructure of the secretory spines in Brasiliopuntia brasiliensis and Nopalea cochenillifera and the chemical composition of the secretion. Secretory spines were processed for light (bright field and confocal) and scanning and transmission (conventional and cytochemical) electron microscopy. The composition of sugars and amino acids was analyzed by high performance liquid chromatography (HPLC). Field observations have shown that the exudate accumulated at the apex of the spines is removed by ants. The ontogenetic, structural and functional aspects of the secretory spines were similar in both species. Secretory spines originate from the areolar meristem, beginning as small protuberances formed by protoderm and fundamental meristem. Spines in the secretory phase presented a) dilated base filled by small cells with thin pecto-cellulosic walls, dense cytoplasm and voluminous nucleus; b) elongated median region composed of fibriform cells with non-lignified walls; and c) apical portion tapered with fusiform cells with non-lignified walls. Vascular tissues are present in the basal region of the spines. Ultrastructurally, the cells of the basal region presented irregular shape and walls with wide plasmodesmata; the middle lamella is swollen at the angles between the cells; mitochondria, rough endoplasmic reticulum, polyribosomes, plastids and abundant dictyosomes occurred in the cytoplasm. The cytochemical analyzes allowed us to identify the dictiosomal origin of vesicles found in the cytoplasm of these cells and the mechanism of secretion release via exocytosis. Chemical analyzes indicated that the exudate released by the secretory spines is rich in sugars; in both species the exudate was sucrose-dominant and with a similar amino acid profile. Our results indicated the occurrence of intense synthesis of hydrophilic substances confirming that these spines are extrafloral nectaries.
Extrafloral nectaries (EFNs) are common and morphologically diverse in Cactaceae, and may be highly modified spines or not, scamiform leaves and specialized epidermal and cortical regions located at the base or around the areoles. However, little is known about the nature of EFNs in cacti, and even if the exudate can be qualified as nectar. We aimed to analyze the morphology, anatomy and ultrastructure of the secretory spines in Brasiliopuntia brasiliensis and Nopalea cochenillifera and the chemical composition of the secretion. Secretory spines were processed for light (bright field and confocal) and scanning and transmission (conventional and cytochemical) electron microscopy. The composition of sugars and amino acids was analyzed by high performance liquid chromatography (HPLC). Field observations have shown that the exudate accumulated at the apex of the spines is removed by ants. The ontogenetic, structural and functional aspects of the secretory spines were similar in both species. Secretory spines originate from the areolar meristem, beginning as small protuberances formed by protoderm and fundamental meristem. Spines in the secretory phase presented a) dilated base filled by small cells with thin pecto-cellulosic walls, dense cytoplasm and voluminous nucleus; b) elongated median region composed of fibriform cells with non-lignified walls; and c) apical portion tapered with fusiform cells with non-lignified walls. Vascular tissues are present in the basal region of the spines. Ultrastructurally, the cells of the basal region presented irregular shape and walls with wide plasmodesmata; the middle lamella is swollen at the angles between the cells; mitochondria, rough endoplasmic reticulum, polyribosomes, plastids and abundant dictyosomes occurred in the cytoplasm. The cytochemical analyzes allowed us to identify the dictiosomal origin of vesicles found in the cytoplasm of these cells and the mechanism of secretion release via exocytosis. Chemical analyzes indicated that the exudate released by the secretory spines is rich in sugars; in both species the exudate was sucrose-dominant and with a similar amino acid profile. Our results indicated the occurrence of intense synthesis of hydrophilic substances confirming that these spines are extrafloral nectaries.
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Palavras-chave
Cacto, Estrutura, Funcionamento, Néctar, Nectário extrafloral, Cactus, Extrafloral nectary, Functioning, Nectar, Structure