USE OF MINERALISED WATER BY KALAHARI WILDLIFE AND ITS EFFECTS ON HABITATS

This study surveyed the use made by springbok, hartebeest, wildebeest and gemsbok, in particular, of mineralised artificial waterholes along the Nossob river in the southern Kalahari and the effects of this use on the delicate surrounding habitats, as a basis for evaluating the uses and limitations of such water in the management of these species. Taking into account the chemical composition of the dissolved salts in the water; the status of the vegetation and conservation trends near water holes; the relative use made of the waterholes by the antelopes; and land use history, it was concluded that: (a) the animals made regular use of the water, some of which was more mineralised than that recommended for domestic stock, including sheep; (b) there was no relationship between the total dissolved salts and animal use, although there may have been some association between gemsbok use and certain ions; (c) wildlife attracted to boreholes had very little effect on the stability of some surrounding habitats, but may have retarded recovery in areas downgraded by past land use, and (d) under these circumstances the effects of this land use were still amply evident after 2¹/₂ decades. From this and other evidence, it is suggested that, at the present level of knowledge, mobile wildebeest populations can be stabilised by the provision of relatively potable water, and mineralised water may be used to raise the levels of springbok, hartebeest and gemsbok populations. However, as the water is less of a limiting factor than for species requiring regular drinking water, the increase in density may be relatively limited and so less of a danger to the maintenance of surrounding habitats.     

Agouti Protein Inhibits the Production of Eumelanin and Phaeomelanin in the Presence and Absence of α-Melanocyte Stimulating Hormone

Melanocytes synthesise two types of melanin: the brown-black eumelanin and the red-yellow phaeomelanin. In mice, the relative proportions of these two melanins are regulated by α-MSH, which preferentially increases the synthesis of eumelanin and by the Agouti protein (AP), the expression of which correlates with the growth of yellow phaeomelanin-containing hair. It has been proposed that AP acts by antagonizing the action of α-MSH at the MCI receptor, although it has been suggested that it may also act independently of α-MSH. In the present study we show that AP inhibits melanogenesis in B16F1 melanoma cells in the presence and absence of α-MSH and also causes dose-related decreases in the synthesis of both eumelanin and phaeomelanin. In the presence of α-MSH AP had a greater effect on eumelanin production and this is consistent with an antagonistic action at the MCI receptor. In the absence of α-MSH however, AP produced similar reductions in the synthesis of both melanins. These changes were not seen in B16G4F cells which lack the MCI receptor, suggesting that even in the absence of α-MSH AP acts at the MCI receptor. How this action is mediated at the intracellular level is not yet clear, although it appears to be associated with a decrease in tyrosinase activity.     

Production and properties of monoclonal antibodies to Solanum nodiflorum mottle sobemovirus

Black raspberry necrosis virus (BRNV) reaches only very low concentrations in herbaceous plants and is difficult to maintain in culture. However, in a mixed culture with an unrelated virus, Solanum nodiflorum mottle (SNMV), in the genus Sobemovirus, the concentration of BRNV particles increases about 1000‐fold. In attempts to produce monoclonal antibodies (MAbs) to BRNV for diagnostic use, purified virus particles from the mixed virus culture were used as immunogen and the resultant antibodies screened against cultures of SNMV alone, BRNV+SNMV and healthy plant extracts. None of the virus‐specific MAbs obtained in this way was specific to BRNV but six were specific to SNMV. Although the original objective was not achieved, the SNMV MAbs were characterised and used to study serological properties of SNMV and other Sobemoviruses. Characterisation of the six SNMV MAbs showed that four were IgG3, one IgG1 and the other IgG2b. SNMV was detected by all six MAbs in ELISA, by five in Western blotting, by three in agarose gel double diffusion tests, but only one was suitable for trapping virus particles in immuno‐electron microscopy (IEM). In Western blotting using virus in sap extracts of Nicotiana clevelandii, each of the five MAbs detected a single major band of Mc. 31 000 in sap containing SNMV, and additional bands of lower mass attributed to degradation of coat protein. In various serological tests, no cross‐reactions were detected between SNMV and seven other viruses from the genus Sobemovirus. However, in IEM but not in Western blotting, significant cross‐reactions were observed between SNMV and Velvet tobacco mottle virus, another species from the genus Sobemovirus. The significance of these different findings is discussed.     

The soil seed bank of Triodia basedowii in relation to time since fire

Triodia basedowii seeds were found almost exclusively within Triodia hummocks, both in the centres and under the edges. Averaged over the whole ground surface, live seed densities in soil and litter were 85-263 m^?2 in stands which had been burnt 9 and > 35 years previously. These live seeds comprised only 56% of all filled grains, and in turn filled grains were present in only about 6% of all fruits. Thus > 4% of fruits contained live seeds. A site burnt 1 year previously had about 35 live seeds m^?2 still ungerminated, but at sites burnt 3 years previously none of the pre-fire seed bank was alive. After fire, juvenile plants were found predominantly around the edges of where hummocks had been before the fire, suggesting that seeds survive fires better around the edges.     

Relationships in consultation

The cause of medicine is advanced by the proper exchange of services between general practitioners and specialists. As a medical group and singly, physicians stand to benefit by strengthening their relationships; and the one to benefit most of all by this combination of services is the patient. Any physician of integrity admits that it is impossible for one physician to know all there is to know about every medical subject. The establishment of rules of conduct to be followed by those who get together to solve a medical problem will promote the use of advisory practice.     

Ultrastructure of Endosymbiotic Chlorella in a Vorticella

SYNOPSIS Observations were made on the ultrastructure of a species of Vorticella containing endosymbiotic Chlorella. The Vorticella , which were collected from nature, bore conspicuous tubercles of irregular size and distribution on the pellicle. Each endosymbiotic algal cell was located in a separate vacuole and possessed a cell wall and cup-shaped chloroplast with a large pyrenoid. The pyrenoid was bisected by thylakoids and surrounded by starch plates. No dividing or degenerating algal cells were observed.