Anatomia foliar de espécies de Chamaecrista Moench. (Leguminosae/Caesalpinioideae) ocorrentes em campo rupestre

• Autor(a) principal: Francino, Dayana Maria Teodoro
• Data de Publicação: 2006
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2528
• topic: Histoquímica; Estruturas secretoras; Estratégia adaptativa; Taxonomia; Histochemistry; Secretory structures; Adaptative strategy; Taxonomy; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::MORFOLOGIA VEGETAL::ANATOMIA VEGETAL

Minas Gerais state flora presents different biomas but little is known about the diversity of its species, some of which secrete natural compounds having well-known biological activity. There is a large number of species of recognized economic interest in the Leguminosae family and in the rupestrial fields of Minas Gerais, totaling 28 of the 351 species included in the endangered species list. This work aims to describe and compare the leaf anatomy of the species of the genus Chamaecrista (Leguminosae/ Caesalpinioideae) occurring in rupestrial field areas at the Itacolomi State Park (Ouro Preto/MG), according to floristic assessment of the Leguminosae family carried out in the area; to evaluate how anatomic parameters can contribute to the understanding of the species adaptative strategies; to identify the anatomic characters of taxonomic value for the genus and to anatomically and histo-chemically characterize the secretory structures found. Branches of Chamaecrista dentata, C. desvau var. langsdorfii, C. hedysaroides, C. mucronata, C. trichopoda were collected and fixed for structural categorization, with the control material being placed at the VIC/UFV Herbarium. Herborized material was used for the species C. rotundata and C. rotundifolia. The samples were diaphanized, dissociated and included in metacrylate, according to standard methodology. Transversal and longitudinal cuts 6μm thickness were obtained of the leaflets of all the species studied. Foliole and petiole samples of the seven species were selected and prepared for electronic scanning microscopy, according to standard methodology. Histochemical tests in fixed or fresh samples collected in the field were carried out to detect the major secondary metabolite classes, according to the recommended protocols. Xeromorphic characters were observed in the seven species of Chamaecrista studied, though differing in amount as well as in their distribution among the species. Some of these characteristics are isobilaterality, compact mesophyll, presence of indument, abundant vascularization and support tissue, thickened epidermis cell walls, etc... All these characteristics contribute to Chamaecrista species adaptation to the adverse conditions of the rupestrial fields. The following was considered as having a diagnostic value: isobilaterality of C. dentata; presence of volumous cells in C. mucronata; idioblasts in the petiole medule of C. rotundata; fibers surrounding the median veins of C. trichopoda extended beyond the apical margin of the foliole, forming an acuminated apex; widened traqueids in C. dentata and C. hedysaroides and the display pattern of the vascular bundles in the petiole of the seven species. These are novel results for the family and could contribute to help delimit the Chamaecrista family. C. dentata glands are discoid with isodiametric thin-walled and dense cytoplasm cells. It displays a short pendunculum and thick cuticle covering the entire structure. At the central portion of the gland apex a single cell protrudes, taking the shape of a tector trichome, apparently constituting the place secretion is eliminated. Morphologically, the C. dentata glands are similar, regardless of the organ or floral verticil evaluated. The histo-chemical tests showed that secretion is lipophylic in nature (positive reaction to sudan IV), specifically neutral lipids (Nile blue) and terpenes of the essential oil type (nadi reagent). Ecologically, the gland can act on the plant s adaptative strategies, helping to reduce excessive water loss during transpiration, since secretion is lipid by nature and deposits itself along the external surface.