J. Coetzee

The phytosociology of the grasslands of the Ba and Ib land types in the Pretoria–Witbank–Heidelberg area

An analysis of the plant communities of the grasslands of the Pretoria–Witbank–Heidelberg area is presented. Releves were compiled in 148 stratified random sample plots. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed fourteen plant communities, and a hierarchical classification, description and ecological interpretation of these plant communities are presented. Each of these plant communities may be regarded as an entity with a unique species composition, and with specific environmental relationships and an inherent forage production potential. The identification, classification and description of these plant communities are not only important for management purposes, but also for the preservation of biotic diversity.

Immunogold Localization and Quantification of Cellular and Subcellular Abscisic Acid, Prior to and During Drought Stress

An immunogold labeling procedure and experimental data are presented, which demonstrate that antibodies produced against a bovine serum albumin-abscisic acid conjugate can be used both to characterize the cellular and subcellular localization of abscisic acid (ABA), and to permit quantitative comparisons of this hormone in the subcellular compartments prior to and at times of drought stress. At the control leaf water potential (approximately -0.45 MPa), a quantitatively similar positive labeling pattern was observed in the chloroplasts and apoplast. A twofold drought stress-induced increase in the apoplastic ABA concentration was observed in the drought stressed leaf tissue (i.e., at a leaf water potential of approximately -1.55 MPa), while the ABA concentration in the chloroplasts did not differ from that of the controls. Three histochemical controls and the physiological observations validated the specificity of the procedure. Based on the labeling patterns we observed and literature cited, the validity of the hypothesis that drought stress induces a release of chloroplastic ABA is questioned. We interpreted our results as providing indirect evidence for a drought stress-induced root source origin for the increased apoplastic ABA concentrations.

An overview of the physical environment and vegetation units of the Ba and Ib land types of the Pretoria-Witbank-Heidelberg area

An analysis of the physical environment and associated vegetation of the study area is presented. Releves were compiled in 265 stratified random plots. Care was taken to avoid severely disturbed areas and ecotones. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed eight vegetation units which can be regarded as distinct ecological units. A hierarchical classification, description and ecological interpretation of the eight vegetation units are presented. These ecological units should be taken into account in the compilation of management programmes for the natural resources of the study area.

The Sub-humid Warm Temperate Mountain Bushveld plant communities of the Pretoria-Witbank-Heidelberg area

An analysis of the plant communities of the Sub-humid Warm Temperate Mountain Bushveld of the PretoriaWitbank-Heidelberg area is presented. Releves were compiled in 44 stratified random sample plots. A T winspan classification, refined by Braun-Blanquet procedures, revealed six plant communities and four variations which can be regarded as distinct ecological units. A hierarchical classification, description and ecological interpretation of the six plant communities and variations are presented. Each of these plant communities may be regarded as a unique entity with its own species composition and specific environmental relationships. The identification, classification and description of these plant communities are not only important for vegetation management purposes but also as a scientific basis for the compilation of policies for the preservation of biotic diversity. ’n Analise van die plantgemeenskappe van die Sub-humiede Warm Gematigde Berg-Bosveld binne die Pretoria–Witbank–Heidelberg studiegebied, word aangebied. Releves is in 44 gestratifiseerde ewekansig gekose monsterpersele saamgestel. ’n T winspan klassifikasie is op die floristiese data uitgevoer, waarna die tabel deur middel van Braun-Blanquet prosedures verder verfyn is. Ses plantgemeenskappe en vier variasies met elk ’n eie floristiese samestelling en produksiepotensiaal is sodoende onderskei. Hierdie gemeenskappe toon elk verwantskappe met sekere omgewingsfaktore en kan dus as aparte ekologiese eenhede beskou word. ’n Hierargiese klassifikasie, beskrywing en ekologiese interpretasie van die plantgemeenskappe en variasies word verskaf. Die identifisering, klassifisering en beskrywing van hierdie plantgemeenskappe is nie net belangrik vir veldbestuursdoeleindes nie, maar ook as wetenskaplike basis vir die opstel van ’n beleid vir die bewaring van biologiese diversiteit.

Plant communities of the Sub-humid Cool Temperate Mountain Bushveld of the Pretoria–Witbank–Heidelberg area, South Africa

An analysis of the plant communities of the Sub-humid Cool Temperate Mountain Bushveld of the Pretoria–Witbank–Heidelberg area within the Grassland Biome of South Africa is presented. Releves were compiled in 33 stratified random sample plots. A default Twinspan classification based on total floristic composition, refined by Braun-Blanquet procedures, revealed five plant communities and seven sub-communities, which all can be regarded as distinct ecological systems. Each of these plant communities may be regarded as a unique natural entity, each with its own species composition, specific environmental conditions and inherent forage production potential. The identification, hierarchical classification, description and ecological interpretation of these plant communities are not only essential for a comprehensive syntaxonomy of South African grassland vegetation, but may also serve as a basis for strategic planning of conservation areas, the preservation of biotic diversity and general veld management planning.

Phytosociology of the wetlands of the Ba and Ib land types in the Pretoria-Witbank-Heidelberg area of the Transvaal, South Africa

An analysis of the plant communities of the wetlands of the Pretoria–Witbank–Heidelberg area of the Transvaal province, South Africa, is presented. Releves were compiled in 40 stratified random sample plots. A T winspan classification, refined by Braun-Blanquet procedures, revealed seven distinct plant communities. A description and ecological interpretation of the plant communities are presented.

Ultrastructure of the stigma and style of Mangifera indica L.

The stigma of Mangifera indica L. is non-papillate and wet, with the style semi-solid. The exudate of the stigma and style is of the mixed type and is transported from vesicles in the secretory cells, via plasmatubules, to the surrounding cell walls. Cell walls of the transmitting tissue of the stigma and style are bilayered. The outer wall layer is typically reticulate and the exudate accumulates between the loosely woven wall fibrils. At the base of the style a specialized obturator, the ponticulus, facilitates the direct passage of the growing pollen tubes towards the embryo sac.

SEM observations on cyanobacteria-infected cycad coralloid roots

In Nostoc -infected coralloid roots of the cycads Encephalartos transvenosus Stapf & Burtt Davy and E. paucidentatus Stapf & Burtt Davy the intercellular cyanobacteria are present in a narrow circular band between the outer and the inner cortex only. When the cyanobacterial density is very great, some intracellular infection is present. In uninfected coralloid roots, cells with a high concentration of phenolic substances are evenly distributed throughout the outer and inner cortical layers, but in infected roots, such cells are restricted largely to the outer cortex. Cyanobionts newly isolated from cycad coralloid roots consist of cells arranged in filaments. Some large spherical structures, similar to those which each leads to the development of a new filament during the late heterocystous phase of the nostocacean life cycle, are found in the roots. On some cyanobacterial cells other micro-organisms are visible. These bacteria-like micro-organisms are probably the heterotrophic bacteria that usually occur in cultures of coralloid root endophytes.

The influence of processing protocol on the ultrastructure of bean leaf cells

Bean leaf cells exhibit ultrastructural damage when glutaraldehyde fixatives or buffer washes are applied for prolonged periods. The maximum times in these processing steps are influenced by the choice of buffer. Prolonged periods in low concentrations of acetone also cause damage. This damage is progressively less obvious in higher concentrations. Extended holding times In anhydrous acetone are possible, especially if phosphate or cacodylate buffers are employed during fixation.

Ultrastructure and cytochemistry of squamulae intravaginales of the marine angiosperm, Halophila ovalis

Small delicate structures found in the leaf bases in vegetative buds of the marine angiosperm Halophila ovalis (R. Br.) Hook. f. showed a fine structure of the component cells typical of secretory cells. They are rich in organelles particularly ER, dictyosomes, ribosomes and mitochondria. Endoplasmic reticulum occurs at two localities in each cell, one surrounding the central nucleus and the other in the peripheral regions close to the plasmalemma. Groups of dictyosomes occur between the two layers of ER and each group is separated from another by interconnecting strands of ER. A mucilaginous secretion accumulates on the cell surface and between the outer and inner layers of cell wall, particularly at the corners. The involvement of ER in the secretion of mucilage is discussed. Staining of ultrathin sections with silver proteinate after thiocarbohydrazide showed the presence of insoluble carbohydrates and histochemical tests with alcian dyes showed the secretion to contain non-sulphated acid polysaccarides. Staining of epoxy resin sections with Coomassie blue R250 indicated that the mucilage secretion on the surface of and within the cell walls also contained proteins. Cellulase–gold complex marked the cellulose wall layers as distinct from the included secretion.