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STRUCTURE AND ULTRASTRUCTURE OF THE EXTRAFLORAL NECTARIES OF CROTON URUCURANA BAILL. (EUPHORBIACEAE)

LEANDRO FREITAS and ADELITA A. S. PAOLI
Boletim de Botânica da Universidade de São Paulo
Vol. 18 (1999), pp. 1-10
Stable URL: http://www.jstor.org/stable/42871476
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
STRUCTURE AND ULTRASTRUCTURE OF THE EXTRAFLORAL NECTARIES OF CROTON URUCURANA BAILL. (EUPHORBIACEAE)
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Abstract

Croton urucurana bears two stalked and patelliform extrafloral nectaries (EFNs) on the petiole. We studied the structure and ultrastructure of the EFNs in relation to nectar secretory process. Three developmental stages of the EFN (pre-secretory, secretory and postsecretory) were recognized. The EFN is constituted by a secretory layer (epidermic and parenchymatic cells), subtended by ground parenchyma and sclerenchymatic cells. Vascular bundles cross the EFN stalk, terminating in the secretory parenchyma. Numerous plasmodesmata have been found in cell walls among parenchymatic cells and connecting these with epidermic cells. It suggests that pre-nectar transport occurs mainly by simplast. Some sugar is storaged in starch grains inside chloroplasts and amyloplasts at the pre-secretory stage. Rough ER and dictyosomes seem to be involved in nectar accumulation and transport. Nectar secretion is carried out by vesicles, whose membranes fuse by the plasmalemma. Nectar is accumulated in the subcuticular space and flows outwards through cuticular channels. The most conspicuous features of the studied EFNs were the presence of both starch grains at the pre-secretory stage and ER profiles at the secretory stage. Croton urucurana possui dois nectários extraflorais (EFNs) pateliformes e pedunculados no pecíolo. Nós estudamos a estrutura e ultra-estrutura dos EFNs, em relação ao processo de secreção do néctar. Três estágios de desenvolvimento do EFN (pré-secretor, secretor e póssecretor) foram caracterizados. O EFN é constituído por uma camada secretora (células epidérmicas e parenquimáticas), por uma camada de preenchimento parenquimática e por células esclerenquimáticas. O sistema vascular do EFN atravessa o pedúnculo da glândula e alcança as células secretoras parenquimáticas. Numerosos plasmodesmas conectam as células parenquimáticas entre si e estas com as células epidérmicas. Isto sugere que o simplasto é a via principal de transporte de pré-néctar. No estágio présecretor, são observados muitos amiloplastos e cloroplastos com grãos de amido, os quais se hidrolisam durante a secreção. Retículo endoplasmático rugoso e dictiossomos parecem estar envolvidos no acúmulo e no transporte de néctar. A secreção do néctar é feita por vesículas, cujas membranas se fundem com a plasmalema. O néctar é acumulado no espaço subcuticular e é expelido através de canais cuticulares. As características mais destacadas dos EFNs estudados foram a presença de grãos de amido no estágio pré-secretor e de elementos do RE no estágio secretor.

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