Características anatômicas, histoquímica das estruturas secretoras e ontogenia de idioblastos da folha de Pothomorphe umbellata (L.) Miq. (Piperaceae) / Anatomical characteristics, histochemistry of the secretory structures and ontogeny of idioblasts on the leaf of Pothomorphe umbellata (L.) Miq. (Piperaceae)

AUTOR(ES)

Cristina Ribeiro Marinho

DATA DE PUBLICAÇÃO

2008

RESUMO

Pothomorphe umbellata, commonly known as pariparoba or capeba, occurs in humid environments and is used in almost entire Brazil due to its medicinal properties. The goals of this work were to understand the leaf anatomy of P. umbellata, to perform the histochemical characterization of the secretory structures present, and to describe the ontogeny of its secretory idioblasts. Regarding the structural characterization, leaf portions were fixed in FAA50 and stored in 70% ethanol. In respect to the study of the idioblasts ontogeny, leaf primordia from the middle portions of the leaf limb, under different developmental stages, were fixed in 2.5% glutaraldehyde in 0.05 M phosphate buffer, pH 7.0. Independently of the type of fixer used, the samples were dehydrated in ethylic series, included in methacrylate, and sliced in rotary microtome with 5m of width, stained with Toluidine Blue, and mounted in coverslip with synthetic resin. The diaphanization was used in the surface study and assessment of the density of the idioblasts. For the leaf micromorphological characterization, samples of leaf primordia, under different developmental stage, were fixed in FAA50, stored in 70% ethanol, and processed for scanning electron microscopy. Concerning the histochemical analysis of the secretory structures, fresh leaves were transversally sectioned and submitted to several dyes and reagents. The leaf of P. umbellata presents thin epidermis and cuticle; it is hypostomatic, dorsiventral and presents supporting tissue restricted to the discontinuous strands of collenchyma. The idioblasts have mixed secretion, which present hydrophobic compounds (oleoresins) and hydrophilic compounds (phenolics and alkaloids). In the secretory trichomes, the secretion is comprised of flavonoids, predominantly. In the vascular bundles of the veins and petiole, there are noticed collapsed elements of the protoxylem, which accumulate mucilage. A large mucilaginous duct is observed in the petioles medulla. The idioblasts present in the region of the veins of larger caliber were developed precociously from the fundamental meristem as well as from the protodermis. In the interveinal region, the idioblasts are originated from initials of the protodermis. At both regions, the idioblasts initials stand out from the other cells of the tissue by their large size, vacuolated cytoplasm, and presence of nucleus and nucleolus more conspicuous. The secretion of the idioblasts is kept in the leaf since the beginning until the leafs senescence, what suggests to this structure a role of chemical defence along the leafs life. The chemical defence, represented by the secretory structures and its secreted metabolites, compensates the lack of mechanical resistance in this species.

ASSUNTO(S)

idioblasto pothomorphe umbellata botanica histoquímica ontogenia histochemistry ontogeny idioblast pothomorphe umbellata

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