Fibras Gelatinosas em Eriosema (DC.) Desv. (Leguminosae): Distribuição e Caracterização Estrutural e Química
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Data
2020-02-17
Autores
Piva, Tayeme Cristina [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Fibras gelatinosas são células especializadas de esclerênquima que possuem uma camada interna altamente modificada de aparência gelatinosa e translúcida, denominada camada-G. Diversas funções são atribuídas as fibras gelatinosas sendo a principal e mais conhecida a sua relação com o lenho de tração. Porém, outras funções de cunho fisiológico e adaptativo, tais como armazenamento de água e manutenção da orientação foliar foram descritas para as fibras gelatinosas. As fibras gelatinosas são reportadas em diversas famílias de angiospermas nos mais diversos ambientes, com isso outras funções podem ser associadas a ocorrência das fibras gelatinosas nos mais diferentes ambientes. O objetivo desse estudo foi analisar as fibras gelatinosas em representantes de Eriosema (DC.) Desv. um gênero de leguminosa comumente encontrado em Cerrado, visando a acessar variações na distribuição e organização das fibras gelatinosas no eixo vegetativo aéreo e subterrâneo, caracterizar a estrutura básica e a histoquímica das paredes celulares. O estudo foi conduzido com 19 táxons coletados em diferentes áreas de Cerrado, sendo amostrados a folha, caule aéreo e órgão subterrâneo. O material foi processado de acordo com técnicas usuais em anatomia e histoquímica vegetal. Uma espécie foi considerada como modelo e foram utilizados os anticorpos LM5 e LM10 marcadores para galactanos e xilanos, respectivamente, nas paredes das fibras gelatinosas. As fibras gelatinosas ocorreram por todo o corpo vegetativo dos táxons de Eriosema estudados, sendo extraxilemáticas em regiões com crescimento primário e xilemáticas em regiões com crescimento secundário. Quanto à organização, na folha as fibras gelatinosas formaram calotas ao redor do floema primário da nervura principal; no caule, se organizaram em cordão cilíndrico completo ao redor do floema em crescimento primário ou em pequenos grupos separados por parênquima em crescimento secundário; no órgão subterrâneo, se organizaram em faixas tangenciais separadas por raios de parênquima xilemático. Em todos os órgãos analisados, as fibras gelatinosas exibiram três camadas parietais distintas: camada-P, incluindo a parede primária e lamela média rica em pectina; a camada-S com número variável de estratos (1-3) geralmente lignificados, e a camada-G, parede celular terciária, não lignificada ou com baixo teor de lignina. De um modo geral, a camada-G foi mais espessa que as demais camadas parietais (P e S). A espécie modelo, apresentou camada-G composta (G+L) formada por lamela não-lignificada (G) e lamela interna lignificada (L) ocorreu na folha (região da nervura principal), regiões do caule em crescimento secundário e órgão subterrâneo. A presença de lignina e xilanos na lamela interna lignificada (L) da camada-G composta foi demonstrada neste estudo, por meio de métodos histoquímico e imunohistoquimico, respectivamente. A ausência de lignina na camada-G, ao conferir propriedades hidrofílicas a esta camada parietal, pode favorecer o armazenamento de água a curto período. Porém, a presença de lignina na camada-G composta (camada-L), como observado no eixo vegetativo aéreo e subterrâneo, ao conferir rigidez e resistência mecânica permitiria proteção em condições ambientais adversas e maior resistência ao fogo. Considerando a abundância de fibras gelatinosas no eixo vegetativo dos táxons de Eriosema aqui analisados, tais fibras podem representar uma adaptação estrutural associada às condições do Cerrado, um ambiente sazonal com temperaturas elevadas e alta incidência luminosa, períodos alternados de alta e baixa disponibilidade de água, solos pobres em nutrientes e aluminotóxicos e queimadas recorrentes. Estudos experimentais com foco na ontogênese da camada-G composta nas fibras gelatinosas de plantas sujeitas a diferentes condições edáficas e climáticas serão necessários para um melhor entendimento sobre os fatores ambientais que favorecem a sua formação.
Gelatinous fibers (G-fibers) are specialized sclerenchyma cells that have a highly modified, translucent, gelatinous appearance inner layer called the G-layer. Several functions are attributed to the G-fibers being the main and best known its relation with the tension wood. However, other physiological and adaptive functions, such as water storage and maintenance of leaf orientation, have been described for G-fibers. G-fibers are reported in several angiosperm families in the most diverse environments, so other functions may be associated with the occurrence of G-fibers in the most different environments. The purpose of this study was to analyze the G-fibers in representatives of Eriosema (DC.) Desv. a genus of legumes commonly found in Cerrado, aiming to access variations in the distribution and organization of G-fibers in the aerial and underground vegetative axis, to characterize the basic structure and histochemistry of cell walls. The study was conducted with 19 taxa collected in different areas of Cerrado, being sampled the leaf, aerial stem and underground organ. The material was processed according to usual techniques in plant anatomy and histochemistry. LM5 and LM10 antibodies that mark galactans and xylans, respectively, were used on the G-fibers walls. G-fibers occurred throughout the vegetative body of the studied Eriosema taxa, being extraxylary in regions with primary growth and xylary in regions with secondary growth. As for the organization, in the leaf the G-fibers formed caps along the primary phloem of the midrib; in the stem, they were organized in complete cylindrical strands around the primary growing phloem or in small groups separated by secondary growing parenchyma; in the underground organ, organized into tangential bands separated by xylem parenchyma rays. In all organs analyzed, the G-fibers exhibited three distinct parietal layers: P-layer, including the primary wall and pectin-rich middle lamella; the S-layer with variable number of strata (1-3) generally lignified, and the G-layer, non-lignified or low lignin tertiary cell wall. In general, the G-layer has always been thicker than the other parietal layers (P and S). Composite G-layer (G+L) formed by non-lignified lamella (G) and lignified internal lamella (L) occurred in the leaf (midrib region), stem regions in secondary growth and underground organ. The presence of lignin and xylans in the lignified internal lamellae (L) of the composed G-layer was demonstrated in this study by histochemical and immunohistochemical methods, respectively. The absence of lignin in the G-layer, by conferring hydrophilic properties to this parietal layer, may favor short-term water storage. However, the presence of lignin in the composed G-layer (L-layer), as observed in the aerial and underground vegetative axis, by conferring rigidity and mechanical strength would allow protection in adverse environmental conditions and greater fire resistance. Considering the abundance of G-fibers in the vegetative axis of the Eriosema taxa analyzed here, such fibers may represent a structural adaptation associated with Cerrado conditions, a seasonal environment with high temperatures and high light incidence, alternating periods of high and low water availability, nutrient-poor and aluminotoxic soils and recurrent burning. Experimental studies focusing on the composite G-layer ontogenesis in G-fibers of plants subjected to different edaphic and climatic conditions will be necessary for a better understanding of the environmental factors that favor their formation.
Gelatinous fibers (G-fibers) are specialized sclerenchyma cells that have a highly modified, translucent, gelatinous appearance inner layer called the G-layer. Several functions are attributed to the G-fibers being the main and best known its relation with the tension wood. However, other physiological and adaptive functions, such as water storage and maintenance of leaf orientation, have been described for G-fibers. G-fibers are reported in several angiosperm families in the most diverse environments, so other functions may be associated with the occurrence of G-fibers in the most different environments. The purpose of this study was to analyze the G-fibers in representatives of Eriosema (DC.) Desv. a genus of legumes commonly found in Cerrado, aiming to access variations in the distribution and organization of G-fibers in the aerial and underground vegetative axis, to characterize the basic structure and histochemistry of cell walls. The study was conducted with 19 taxa collected in different areas of Cerrado, being sampled the leaf, aerial stem and underground organ. The material was processed according to usual techniques in plant anatomy and histochemistry. LM5 and LM10 antibodies that mark galactans and xylans, respectively, were used on the G-fibers walls. G-fibers occurred throughout the vegetative body of the studied Eriosema taxa, being extraxylary in regions with primary growth and xylary in regions with secondary growth. As for the organization, in the leaf the G-fibers formed caps along the primary phloem of the midrib; in the stem, they were organized in complete cylindrical strands around the primary growing phloem or in small groups separated by secondary growing parenchyma; in the underground organ, organized into tangential bands separated by xylem parenchyma rays. In all organs analyzed, the G-fibers exhibited three distinct parietal layers: P-layer, including the primary wall and pectin-rich middle lamella; the S-layer with variable number of strata (1-3) generally lignified, and the G-layer, non-lignified or low lignin tertiary cell wall. In general, the G-layer has always been thicker than the other parietal layers (P and S). Composite G-layer (G+L) formed by non-lignified lamella (G) and lignified internal lamella (L) occurred in the leaf (midrib region), stem regions in secondary growth and underground organ. The presence of lignin and xylans in the lignified internal lamellae (L) of the composed G-layer was demonstrated in this study by histochemical and immunohistochemical methods, respectively. The absence of lignin in the G-layer, by conferring hydrophilic properties to this parietal layer, may favor short-term water storage. However, the presence of lignin in the composed G-layer (L-layer), as observed in the aerial and underground vegetative axis, by conferring rigidity and mechanical strength would allow protection in adverse environmental conditions and greater fire resistance. Considering the abundance of G-fibers in the vegetative axis of the Eriosema taxa analyzed here, such fibers may represent a structural adaptation associated with Cerrado conditions, a seasonal environment with high temperatures and high light incidence, alternating periods of high and low water availability, nutrient-poor and aluminotoxic soils and recurrent burning. Experimental studies focusing on the composite G-layer ontogenesis in G-fibers of plants subjected to different edaphic and climatic conditions will be necessary for a better understanding of the environmental factors that favor their formation.
Descrição
Palavras-chave
Camada-G, Camada-G composta, Cerrado, Fibras gelatinosas, Parede celular, Cell wall, Composed G-layer, G-fibers, G-layer