Structure and histochemistry of the stigmatic and transmitting tissues of Rodriguezia venusta (Orchidaceae) during flower development

Stigma and transmitting tissue are floral structures essential for sexual reproduction of angiosperms and can be useful features in taxonomic studies. Rodriguezia venusta (Lindl.) Rchb. f. is an epiphytic orchid belonging to the large subfamily Epidendroideae. The present study describes the structure and histochemistry of the stigmatic and transmitting tissues of R. venusta during flower development. The differentiation and the secretory activity of the stigmatic and transmitting tissues are already visible in the initial stages of development of the flower bud studied. These tissues, which have a reticulated appearance, predominantly secrete mucilaginous material that is accumulated in the intercellular spaces. The stigma is covered by a cuticle that extends over the internal surface of the central canal in the transmitting tissue in this apical portion. In the stigma, the cuticle appears to have micropores, and in the intercellular spaces, there are small spherical bodies that stain for lipids, proteins and total carbohydrates. The functions of these bodies still remain unknown.583233240Universidade Estadual do Sudoeste da Bahia - UESB, Bahia, Brazi

Structural and histochemical characterisation of the colleters of Rodriguezia venusta (Orchidaceae)

Colleters are secretory structures present in many dicotyledon families, but they have not yet been reported for the Orchidaceae. However, the orchid Rodriguezia venusta was observed to possess secretory trichomes on the adaxial side of the bracts subtending. oral buds that can be interpreted to be colleters. The present work describes the anatomy and histochemistry of these structures. These bracteal trichomes are multicellular, uniseriate, and densely spaced near the region where the bract attaches to the inflorescence. The secretions of these trichomes are mucilaginous and apparently exclusively constituted by carbohydrates, and they appear to act as a lubricant that facilitates the young. oral bud to slide over the bract as it grows. In light of these characteristics, it is proposed that these secretory trichomes should be considered to be 'colleters'.56216116

Effects of anoxia on root ultrastructure of four neotropical trees

The root ultrastructure of seedlings grown in anaerobic conditions was investigated in four neotropical species: Sesbania virgata, Erythrina speciosa, Sebastiania commersoniana (all present in waterlogged or flooded areas), and Schizolobium parahyba (that occupies mainly dry areas). Anaerobiosis induced an increase in the size of mitochondria, dilatation of cristae and of the endoplasmic reticulum, and fragmentation or concentric arrangement of reticulum saccules. The ultrastructural alterations were reversible only for S. virgata and E. speciosa. The seedlings of S. parahyba and S. commersoniana were more sensitive to oxygen deprivation and presented extensive cell disruption. The results are discussed in terms of energy supply.224416719910

Xyloglucan mobilisation in cotyledons of developing plantlets of Hymenaea courbaril L. (Leguminosae-Caesalpinoideae)

Many seeds contain storage compounds that are used by the embryo/plantlet as a source of nutrients after germination. In seeds of Hymenaea courbaril, a leguminous tree, the main reserve consists of a structurally unusual xyloglucan stored in thickened walls of the cotyledon cells. The present work aimed to study H. courbaril xyloglucan metabolism during and after germination in order to compare its degrading system with the other known xyloglucan containing seeds. Polysaccharide degradation occurred after germination between 35 and 55 days after planting. The activities of alpha-xylosidase, beta-glucosidase, beta-galactosidase and XET rose during the period of xyloglucan disassembling but a low level of endo-beta-glucanase activity was detected, suggesting that this XET has high affinity for the oligosaccharides. The pH optimum of beta-galactosidase was different from the alpha-xylosidase, beta-glucosidase and XET optima suggesting that the former may be important in the control of the mobilisation process. A tentative model for xyloglucan disassembling in vivo is proposed, where beta-galactosidase allows the free oligosaccharides to bypass a transglycosylation cycle and be disassembled by the other exo-enzymes. Some ecophysiological comparisons among H. courbaril and other xyloglucan storing seeds are discussed. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.154211712

Structural and chemical changes in cocoa (Theobroma cacao L) during fermentation, drying and roasting

Cocoa seeds and pulp were fermented for 144h, followed by natural drying. The tegument was removed and the cotyledons were broken into nibs which were roasted at 150 degreesC for 30 min. Non-fermented material, material fermented for 24, 48 and 72h, material fermented for 144h and then dried, and also the roasted nibs, were all prepared for chemical and microscopic analyses. Light microscopy revealed the presence of anionic and cationic residues and of neutral sugars. During fermentation there was a reduction in the cytoplasmic content of phenolic compounds and in the number of protein bodies. The cell wall showed a reduction in anionic residues and a loss of crystallinity. These alterations were maximum after 72 h. Drying and roasting increased the number of damaged cells and reduced the amount of cytoplasmic material. The chemical analyses generally confirmed the microscopy results. The concentration of amino-terminal groups and total free amino acids increased during fermentation (up to 72 h), but returned to the initial values after roasting. The principal chemical changes were related to reducing sugars, free amino acids, proteins and phenols, and PCA was suggested as a useful tool to compare different samples. Microscopic analysis revealed the degradation of protein and phenolic bodies and cellular damage during roasting. (C) 2000 Society of Chemical Industry.81228128