Seedlings of white clover (Trifolium repens L.) were inoculated with several strains of mycorrhizal fungi and were cultured for sufficient time to allow the fungal endophytes to develop and mature. The roots were then subjected to a simple freezefracture, freeze-dry procedure in preparation for scanning electron microscopy and X-ray microanalysis. The morphology of the endophytes was observed and qualitative X-ray data were obtained indicating an accumulation of elements within mature arbuscles. Evidence of endophyte breakdown, accompanied by a reduction of the expected phosphorus concentrations, was also obtained and its implications are discussed.
SUMMARYSeasonal changes in the content of Ca and Mg in leaf hlades collected from mature kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa] vines in a highproducing orchard were measured by a sequential fractionation procedure (14 M acetic acid, 0-25 M HCl and residual). Total Ca and Mg concentrations decreased within the first 4 weeks of growth, but increased linearly thereafter to be 1322 and 197 //mol g~^ dry weight, respectively, by leaf fall. Total quantities of Ca and Mg accumulated at this time were approximately 2500 and 380/imol per blade. Calcium oxalate, dissolved in the HCl extract, was the predominant fraction at every harvest, accounting for up to 79 % of the total Ca content shortly after leaf emergence, and decreasing to 42 % at leaf fall. The quantity of physiologically active Ca (acetic acid-soluhle) ranged from a minimum of 15 % (8 weeks after emergence) to a maximum of 41 % at the end of the season. Forms of Ca remaining in the solid residue after extraction made only a minor contribution (3 to 21 %) to the total content at any time during the season. In contrast, however, 89 to 96% of the total Mg was extracted by acetic acid at every harvest, with the remainder dissolved hy HCl. Scanning electron microscopy and X-ray microanalysis of the lamina of mature leaves indicated the presence of two crystalline, Ca-rich products which differed in their morphology, location and distribution. Large styloids (120 to 270 //m in length) were concentrated in idioblasts adjacent to vascular tissue, while bundles of four-sided raphides, containing wedge-shaped apices, were located predominantly hetween the major transport vessels of the vascular tissue. X-ray diffraction analysis of crystalline isolates confirmed that both morphological forms are calcium oxalate monohydrate (whewellite).
The attachment of Escherichia coli and Streptococcus bovis of bovine faecal origin to soil clay particles has been examined using scanning electron microscopy. Both organisms produce extracellular polymers through which the cells form bridges to clay surfaces. Differences in the extent of cell‐to‐particle bridging between E. coli‐and S. bovis‐soil complexes are explained in terms of the charge characteristics of the cells and the properties of the exopolymers.
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