Morfologia, funcionamento e influência de fatores exógenos no sistema secretor de óleo em espécies vegetais com ênfase no papel do citoesqueleto no processo de secreção
Carregando...
Data
2018-01-16
Autores
Tozin, Luiz Ricardo dos Santos
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
A morfologia, histoquímica e ultraestrutura dos tricomas glandulares têm sido estudadas em muitas espécies vegetais. Entretanto, alguns aspectos têm sido pouco abordados, como o envolvimento do citoesqueleto na morfologia e funcionamento glandular. Estudo recente demonstrou a relação entre a predominância de filamentos de actina e microtúbulos em células secretoras e a composição da secreção em tricomas glandulares. Além disso, pesquisas têm comprovado o envolvimento dos elementos do citoesqueleto na origem e manutenção dos tricomas tectores em plantas, sem informações para os tricomas glandulares. Sabe-se que o funcionamento do citoesqueleto está relacionado com a disponibilidade do cálcio, sendo que baixas concentrações desse íon podem prejudicar processos modulados por microtúbulos e actina. Apesar da presença de tricomas glandulares representar um caráter constitutivo em diversas espécies vegetais, fatores exógenos podem influenciar o desenvolvimento e o funcionamento glandular. Estudos têm mostrado que o ataque de herbívoros induz a formação de tricomas glandulares, levando a produção de substâncias com potencial repelente ou inseticida. Os objetivos desse trabalho foram investigar o papel do citoesqueleto na morfogênese e funcionamento de tricomas glandulares e no transporte lipídico em células secretoras de óleo, além de investigar a influência da herbivoria no desenvolvimento e funcionamento de tricomas glandulares. Foram estudadas duas espécies de Lamiaceae (Hyptis villosa e Ocimum gratissimum) e a espécie modelo Nicotiana benthamiana. Experimentos com drogas inibidoras da polimerização do citoesqueleto e doses decrescentes de cálcio foram realizados com O. gratissimum e H. villosa. Plantas de N. benthamiana foram infiltradas com Agrobacterium modificado para marcação de gotas de óleo, plastídios, retículo endoplasmático, actina e microtúbulos. Além disso, indivíduos de O. gratissimum foram submetidos ao ataque de formigas cortadeiras. Análises estruturais foram realizadas aos microscópios de luz (campo claro e confocal) e eletrônico (varredura e transmissão). Além disso, foram realizadas análises de composição química de voláteis e de trocas gasosas. Três morfotipos de tricomas glandulares foram identificados em O. gratissimum; microtúbulos foram intensamente marcados em células secretoras de lipídios, enquanto filamentos de actina foram fortemente marcados em células secretoras de compostos hidrofílicos. As drogas desestabilizantes do citoesqueleto e baixos níveis de Ca+2 não afetaram a morfologia externa dos tricomas; entretanto, acarretaram danos estruturais nas paredes e no protoplasto das células secretoras em O. gratissimum e H. villosa. A composição química dos voláteis não foi alterada pelos diferentes níveis de Ca+2. Em N. benthamiana foi observado que as gotas de óleo se movimentam no citoplasma pelo retículo endoplasmático ancorado aos filamentos de actina, sugerindo um mecanismo de diferente do descrito em células animais. A herbivoria promoveu respostas diferenciais de cada morfotipo glandular em O. gratissimum sugerindo a ocorrência de uma compartimentalização de funções entre os tricomas; além disso, foram detectadas alterações na composição dos componentes voláteis produzidos. Esse trabalho envolveu diferentes abordagens, várias delas inéditas, para o estudo do sistema secretor de óleo em plantas. Diferentes aspectos sobre o sistema secretor de óleo em espécies vegetais foram elucidados, gerando novas perspectivas para estudos mais aprofundados.
The morphology, histochemistry and ultrastructure of glandular trichomes have been studied in many plant species. However, some aspects have been poorly approached, such as the involvement of the cytoskeleton on the gland morphology and functioning. Recent study demonstrated a relation between the predominance of actin filaments and microtubules in secretory cells and the secretion composition in glandular trichomes. In addition, researches have proven the involvement of the cytoskeletal elements in the origin and maintenance of non-glandular trichomes in plants, with no information for glandular trichomes. It is known that the cytoskeleton functioning is related with calcium availability and that low concentration of this ion can harm process modulated by actin filaments and microtubules. Despite the presence of glandular trichomes is a constitutive character in several plant species, exogenous factors can influence their development and functioning. Studies have showed that herbivore attacks induce the glandular trichomes formation, leading to the production of substances with repellent and insecticide potential. This work aimed to investigate the role of cytoskeleton in the glandular trichome morphogenesis and functioning, and in the lipid transport in oil secretory cells, in addition to investigate the influence of herbivory in the glandular trichomes formation and functioning. We studied two Lamiaceae species (Hyptis villosa and Ocimum gratissimum) and the model species Nicotiana benthamiana. Experiments with inhibitors of cytoskeletal element polymerization and decreasing calcium levels were performed with H. villosa and O. gratissimum. N. benthamiana plants were infiltrated with modified Agrobacterium for labeling lipid drops, plastids, endoplasmic reticulum, actin filaments and microtubules. In addition, individuals of O. gratissimum were submitted to leaf-cutter ants attack. Structural analysis were performed using light (bright field and confocal) and electronic (scanning and transmission) microscopes. In addition, we performed analysis of the the chemical composition of the volatile components and of gas-exchanges. Three morphotypes of glandular trichomes were identified in O. gratissimum; microtubules were intensely labeled in secretory cells of lipophilic compounds, while actin filaments were strongly labeled in secretory cells of hydrophilic substances. The inhibitors of cytoskeletal elements polymerization and low levels of calcium did not affect the external morphology of the trichomes; however, lead to structural damages in the cell wall and protoplast of secretory cells of O. gratissimum and H. villosa. The chemical composition of volatile components was not affected by low levels of Ca+2. In N. benthamiana we observed that lipid drops move in the cytoplasm by the endoplasmic reticulum anchored on the actin filaments; this suggests a different mechanism described for animal cells. The herbivory promoted differential answers in each glandular trichome morphotype in O. gratissimum; this suggests the occurrence of a compartmentalization of functions among the trichomes; in addition, we detected alterations in the chemical composition of the volatile components produced by attacked plants. This work involved different approaches, several of them innovative, for the study of the oil secretory system in plants. Different aspects about the oil secretory system in plants were elucidated, opening new avenues for further studies.
The morphology, histochemistry and ultrastructure of glandular trichomes have been studied in many plant species. However, some aspects have been poorly approached, such as the involvement of the cytoskeleton on the gland morphology and functioning. Recent study demonstrated a relation between the predominance of actin filaments and microtubules in secretory cells and the secretion composition in glandular trichomes. In addition, researches have proven the involvement of the cytoskeletal elements in the origin and maintenance of non-glandular trichomes in plants, with no information for glandular trichomes. It is known that the cytoskeleton functioning is related with calcium availability and that low concentration of this ion can harm process modulated by actin filaments and microtubules. Despite the presence of glandular trichomes is a constitutive character in several plant species, exogenous factors can influence their development and functioning. Studies have showed that herbivore attacks induce the glandular trichomes formation, leading to the production of substances with repellent and insecticide potential. This work aimed to investigate the role of cytoskeleton in the glandular trichome morphogenesis and functioning, and in the lipid transport in oil secretory cells, in addition to investigate the influence of herbivory in the glandular trichomes formation and functioning. We studied two Lamiaceae species (Hyptis villosa and Ocimum gratissimum) and the model species Nicotiana benthamiana. Experiments with inhibitors of cytoskeletal element polymerization and decreasing calcium levels were performed with H. villosa and O. gratissimum. N. benthamiana plants were infiltrated with modified Agrobacterium for labeling lipid drops, plastids, endoplasmic reticulum, actin filaments and microtubules. In addition, individuals of O. gratissimum were submitted to leaf-cutter ants attack. Structural analysis were performed using light (bright field and confocal) and electronic (scanning and transmission) microscopes. In addition, we performed analysis of the the chemical composition of the volatile components and of gas-exchanges. Three morphotypes of glandular trichomes were identified in O. gratissimum; microtubules were intensely labeled in secretory cells of lipophilic compounds, while actin filaments were strongly labeled in secretory cells of hydrophilic substances. The inhibitors of cytoskeletal elements polymerization and low levels of calcium did not affect the external morphology of the trichomes; however, lead to structural damages in the cell wall and protoplast of secretory cells of O. gratissimum and H. villosa. The chemical composition of volatile components was not affected by low levels of Ca+2. In N. benthamiana we observed that lipid drops move in the cytoplasm by the endoplasmic reticulum anchored on the actin filaments; this suggests a different mechanism described for animal cells. The herbivory promoted differential answers in each glandular trichome morphotype in O. gratissimum; this suggests the occurrence of a compartmentalization of functions among the trichomes; in addition, we detected alterations in the chemical composition of the volatile components produced by attacked plants. This work involved different approaches, several of them innovative, for the study of the oil secretory system in plants. Different aspects about the oil secretory system in plants were elucidated, opening new avenues for further studies.
Descrição
Palavras-chave
actina, herbivoria, Lamiaceae, microtúbulos, Nicotiana benthamiana, óleo essencial, tricomas, ultraestrutura, actin, essential oil, herbivory, microtubules, trichomes, ultrastructure