Evidence for diet partitioning among three coexisting native freshwater fishes in South Africa's Cape Fold Ecoregion

The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa's Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.     

A New Dominant Retinal Degeneration (Rd4) Associated with a Chromosomal Inversion in the Mouse

An autosomal dominant retinal degeneration, calledRd4,was found in a stock carrying the inversion In(4)56Rk, which was induced in a DBA/2J male. The inversion encompasses nearly all of Chromosome 4. It is homozygous lethal and in heterozygotes is always associated with retinal degeneration. In affected mice, the retinal outer nuclear and plexiform layers begin to reduce at 10 days of age, showing total loss at 6 weeks. The recordable electroretinograms (ERG) showed poorly at 3 to 6 weeks and were barely detected after 6 weeks of age. Retinal vessel attenuation, pigment spots, and optic atrophy appeared in the fundus at 4 weeks of age.Rd4has not recombined with the inversion in an outcross, suggesting that theRd4locus is located very close to or is disrupted by one of the breakpoints of the inversion, either near the centromere or near the telomere. A human homolog would be expected to be located on human chromosomes 1p or 8q.     

Cloning of genes whose expression is correlated with mitosis and localized in dividing cells in root caps of Pisum sativum L.

Removal of border cells from pea roots synchronizes and induces root cap cell division, wall biogenesis and differentiation. Three messages which are expressed differentially in such induced root caps have been cloned. Sequence analyses showed that the PsHRGP1-encoded protein has high homology with a hydroxyproline-rich glycoprotein. The PsCaP23-encoded protein has high homology with an alfalfa callus protein or translationally controlled human or mouse tumor protein P23. The PsRbL41-encoded protein has high homology with a highly basic 60S ribosomal protein L41. In situ hybridization showed that PsHRGP1, PsCaP23 and PsRbL41 messages are localized within dividing cells of the root cap. PsHRGP1 is highly expressed in uninduced root caps, but its message is repressed by 10–11 times as soon as cell division and differentiation begin. Expression of PsHRGP1 recovers to higher than (180%) its initial level in 30 min. PsHRGP1 is root-specific. PsCaP23 and PsRbL41 messages increase ca. 3-fold within 15 min after root cap induction. All three genes represent small families of 3–5 closely related genes in the pea genome.     

Transport of virally expressed green fluorescent protein through the secretory pathway in tobacco leaves is inhibited by cold shock and brefeldin A

Potato virus X (PVX) has been used as an expression vector to target the green fluorescent protein (GFP) from the jellyfish Aequorea victoria to the endoplasmic reticulum (ER) of tobacco (Nicotiana clevelandii L.) leaves. Expression of free GFP resulted in strong cytoplasmic fluorescence with organelles being imaged in negative contrast. Translocation of GFP into the lumen of the ER was mediated by the use of the sporamin signal peptide. Retention of GFP in the ER was facilitated by the splicing of the ER retrieval/retention tetrapeptide, KDEL to the carboxy terminus of GFP. Fluorescence of GFP was restricted to a labile cortical network of ER tubules with occasional small lamellae and to streaming trans-vacuolar strands. Secretion of ER-targeted GFP was inhibited both by cold shock and low concentrations of the secretory inhibitor brefeldin A. However, both prolonged cold and prolonged incubation in brefeldin A resulted in the recovery of secretory capability. In leaves infected with the GFP-KDEL construct, high concentrations of brefeldin A induced the tubular network of cortical ER to transform into large lamellae or sheets which reverted to the tubular network on removal of the drug. Received: 8 October 1998 / Accepted: 16 November 1998     

The turnover of cell surface proteins of carrot protoplasts

The covalent modification of cell surface proteins with N-hydroxysuccinimide esters of biotin was used to develop a strategy for following the turnover of proteins on the surface of carrot (Daucus carota L.) protoplasts. A biotinylation/internalisation assay was established which enabled the turnover of cell surface proteins to be examined by biochemical and immunocytochemical techniques. The detection of biotinylated proteins after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting indicated that a variety of proteins on the surface of the protoplasts were covalently modified. Immunolocalisation of biotinylated proteins in protoplasts directly after their derivatisation, demonstrated that the proteins were initially restricted to the cell surface. Incubation of biotinylated protoplasts at 25 °C for 1 h resulted in the detection of biotin-labelled proteins on the cell surface and intracellularly. A small proportion of these proteins was associated with coated pits, the Golgi apparatus and vacuolar compartments. Biochemical analysis of internalised proteins revealed that a polypeptide of approximate M_r 100 000 was internalised by the protoplasts. Immunolabelling of a biotinylated protein of M_r 100 000 by an antibody raised against an isoform of a tobacco plasma-membrane H⁺-ATPase, strongly suggests that the plasma-membrane H⁺-ATPase is internalised by carrot protoplasts. The implications of these results are discussed within the context of endocytosis in plants. Received: 13 July 1998 / Accepted: 11 November 1998     

Effect of pectin methylesterase gene expression on pea root development.

Expression of an inducible gene with sequences common to genes encoding pectin methylesterase (PME) was found to be tightly correlated, both spatially and temporally, with border cell separation in pea root caps. Partial inhibition of the gene's expression by antisense mRNA in transgenic pea hairy roots prevented the normal separation of root border cells from the root tip into the external environment. This phenotype was correlated with an increase in extracellular pH, reduced root elongation, and altered cellular morphology. The translation product of the gene exhibited PME activity in vitro. These results are consistent with the long-standing hypothesis that the demethylation of pectin by PME plays a key role in cell wall metabolism.     

The ecological integrity of the lower Olifants River,Limpopo province,South Africa: 2009–2015 – Part B: Tributaries of the Olifants River

Monitoring on the Lowveld reaches of the Olifants River, Limpopo River System, and its Steelpoort, Blyde, Klaserie and Selati tributaries was initiated in 2009. Analysis of the 2009–2015 data from four Olifants River sites showed deterioration in the river’s ecological condition between where it enters the Lowveld and where it enters the Kruger National Park, with a slight recovery within the Kruger National Park. Physico-chemical, aquatic macroinvertebrate and fish data collected in 2009–2015 at six sites on the Steelpoort, Blyde, Klaserie and Selati tributaries of the Olifants River corroborated the ecological condition of these tributaries. The Selati was the most polluted and was in a critically modified condition, whereas the Klaserie and Steelpoort were in fair condition and the Blyde was in good condition. The Selati appeared to have a significant negative impact on the water quality, macroinvertebrates and fish of the Olifants River within the Kruger National Park.     

Human health risks of metals and metalloids in muscle tissue of Synodontis zambezensis Peters, 1852 from Flag Boshielo Dam,South Africa

Muscle tissue from 63 Synodontis zambezensis collected bimonthly in 2013 at Flag Boshielo Dam were analysed for metals and metalloids in a desktop human health risk assessment. The Hazard Quotient, based on a weekly meal of 67 g of fish muscle, exceeded the maximum acceptable level of one for lead, cobalt, cadmium, mercury, arsenic and selenium. The concentrations of these elements were higher in 2013 than those recorded in 2009 and 2012 in other fish species from Flag Boshielo Dam and these may pose a long-term health risk if consumed regularly by impoverished rural communities reliant on fish as a source of protein.