The prickly pear (Opuntia ficus-indica [Cactaceae]) in South Africa: Utilization of the naturalized weed,and of the cultivated plants

In spite of successful biological control efforts, vast areas of South Africa remain infested with the spiny prickly pear weed, Opuntia ficus-indica. These remnant populations, which vary from sparse to dense and which are more or less stable, are confined mainly to the eastern Cape. They provide a popular fruit and a limited source of income for certain sectors of the population in these areas. In terms of existing legislation, there are, however, restrictions on the large-scale utilization of these fruit. A novel method for mass-rearing the cochineal insect, Dactylopius coccus, for the commercial production of a red dye (carminic acid) has been developed. The cultivated spineless prickly pear has recently been enjoying renewed attention from researchers and growers alike. Whereas it has traditionally been cultivated mainly as a droughtresistant fodder crop, and is still popular as such, it is now increasingly recognised as a fruit, in its own right, with considerable promise as a commercial crop for local and export markets. There is also a need to encourage the use of very young cladodes (nopalitos) as a highly nutritious vegetable for human consumption in South Africa.     

The β-Hemolysin and Intracellular Survival of Streptococcus agalactiae in Human Macrophages

S. agalactiae (group B streptococci, GBS) is a major microbial pathogen in human neonates and causes invasive infections in pregnant women and immunocompromised individuals. The S. agalactiae β-hemolysin is regarded as an important virulence factor for the development of invasive disease. To examine the role of β-hemolysin in the interaction with professional phagocytes, the THP-1 monocytic cell line and human granulocytes were infected with a serotype Ia S. agalactiae wild type strain and its isogenic nonhemolytic mutant. We could show that the nonhemolytic mutants were able to survive in significantly higher numbers than the hemolytic wild type strain, in THP-1 macrophage-like cells and in assays with human granulocytes. Intracellular bacterial multiplication, however, could not be observed. The hemolytic wild type strain stimulated a significantly higher release of Tumor Necrosis Factor-α than the nonhemolytic mutant in THP-1 cells, while similar levels of the chemokine Interleukin-8 were induced. In order to investigate bacterial mediators of IL-8 release in this setting, purified cell wall preparations from both strains were tested and found to exert a potent proinflammatory stimulus on THP-1 cells. In conclusion, our results indicate that the β-hemolysin has a strong influence on the intracellular survival of S. agalactiae and that a tightly controlled regulation of β-hemolysin expression is required for the successful establishment of S. agalactiae in different host niches.     

Assembly of heterodimeric luciferase after de novo synthesis of subunits in rabbit reticulocyte lysate involves hsc70 and hsp40 at a post-translational stage.

Heterodimeric luciferase from Vibrio harveyi had been established as a unique model enzyme for direct measurements of the effects of molecular chaperones and folding catalysts on protein folding and subunit assembly after de novo synthesis of subunits in rabbit reticulocyte lysate. It was observed that luciferase assembly can be separated in time from synthesis of the two subunits and that under these post-translational conditions assembly was inhibited by either ATP depletion or inhibition of peptidylprolyl cis/trans isomerases, that is, by addition of cyclosporin A or FK506. Furthermore, it was observed that the inhibitory effect of FK506 on luciferase assembly can be suppressed by addition of purified cyclophilin, thereby providing the first direct evidence for the involvement of peptidylprolyl cis/trans isomerases in protein biogenesis in the eukaryotic cytosol. Here the ATP requirement in luciferase assembly has been characterized. Depletion of either Hsp90 or CCT from reticulocyte lysate did not interfere with luciferase assembly. However, addition of purified Hsc70 stimulated luciferase assembly. While addition of purified Hsp40 did not have any effect on luciferase assembly, the stimulatory effect of Hsc70 was further increased by Hsp40. Thus, after synthesis of the two subunits in reticulocyte lysate assembly of heterodimeric luciferase involves Hsc70 and its co-chaperone Hsp40. Therefore, Hsc70 aids protein biogenesis in the eukaryotic cytosol not only at the levels of nascent polypeptide chains and precursor proteins that have to be kept competent for transport into cell organelles, but also at the level of subunits that have to be kept competent for assembly.     

The relationship between turgor pressure and titratable acidity in mesophyll cells of intact leaves of a Crassulacean-acid-metabolism plant,Kalanchoe daigremontiana Hamet et Perr

Day/night changes in turgor pressure (P) and titratable acidity content were investigated in the (Crassulacean-acid-metabolism (CAM) plant Kalanchoe daigremontiana. Measurements of P were made on individual mesophyll cells of intact attached leaves using the pressure-probe technique. Under conditions of high relative humidity, when transpiration rates were minimal, changes in P correlated well with changes in the level of titratable acidity. During the standard 12 h light/12 h dark cycle, maximum turgor pressure (0.15 MPa) occurred at the end of the dark period when the level of titratable acidity was highest (about 300 eq H⁺·g^-1 fresh weight). A close relationship between P and titratable acidity was also seen in leaves exposed to perturbations of the standard light/dark cycle. (The dark period was either prolonged, or else only CO₂-free air was supplied in this period). In plants deprived of irrigation for five weeks, diurnal changes in titratable acidity of the leaves were reduced (H=160 eq H⁺·g^-1 fresh weight) and P increased from essentially zero at the end of the light period to 0.02 MPa at the end of the dark period. Following more severe water stress (experiments were made on leaves which had been detached for five weeks), P was zero throughout day and night, yet small diurnal changes in titratable acidity were still measured. These findings are discussed in relation to a hypothesis by Lüttge et al. 1975 (Plant Physiol. 56,613-616) for the role of P in the regulation of acidification/de-acidification cycles of plants exhibiting CAM.Abbreviations CAM crassulacean acid metabolism - FW fresh weight - P turgor pressure     

Red blood cell aging--membrane skeleton alteration and IgG receptor expression

Investigations were performed on aging of erythrocytes. It has been assumed that structural changes of the membrane result after exposer of the cells to certain environmental influences in vivo or in vitro. Cell aging can be connected with varying combinations of membrane structure disturbances. It is postulated that the messenger which signals membrane structure lesion is involved in a mechanism given by the expression of immunoglobulin G (IgG) receptor sites which bind autologous IgG1 and IgG3. This antibodies are cytophilic for macrophages. The performed studies demonstrated that an intact molecular arrangement of the membrane skeleton is not only a supposition for stabilization of the membrane asymmetry but also for IgG receptor masking to prevent an early elimination of the red blood cells from the organism.     

Ouabain-binding site of (Na+ + K+)-ATPase in right-side-out vesicles has not an externally accessible SH group

The fluorescing sulfhydryl reagent N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM) inactivates purified (Na+ + K+)-ATPase at 20 microM. This inactivation results in a decrease of the ouabain-binding capacity of the enzyme. Treatment of (Na+ + K+)-ATPase, embedded in right-side-out-oriented vesicles, by DACM does not affect ouabain binding to the enzyme. Incorporation of DACM into the alpha subunit of (Na+ + K+)-ATPase embedded in right-side-out vesicles is also not affected by the presence or absence of 100 microM ouabain. It is therefore concluded that a sulfhydryl group does not reside within the ouabain-binding site of (Na+ + K+)-ATPase.     

Regulated nitrate transport in the cyanobacterium Anacystis nidulans.

Intracellular accumulation of nitrate, indicative of the operation of an active nitrate transport system, has been measured in intact cells of the cyanobacterium Anacystis nidulans. The ability of the cells to accumulate nitrate was effectively hindered by either ammonium addition or selective inhibition of CO2 fixation by DL-glyceraldehyde, with the effect of either compound being prevented by previously blocking ammonium assimilation. The results support the contention that nitrate utilization in cyanobacteria is regulated at the level of nitrate transport through the concerted action of ammonium assimilation and CO2 fixation.     

Detection of induced mitotic chromosome loss in Saccharomyces cerevisiae--an interlaboratory study

The diploid yeast strain D61.M was used to study induction of mitotic chromosome loss. The test relies upon the uncovering and expression of multiple recessive markers reflecting the presumptive loss of the chromosome VII homologue carrying the corresponding wild-type alleles. The underlying 'loss event' is probably complex since the predicted centromere-linked lethal tetrad segregations for chromosome VII are not recovered. Instead, the homologue bearing the multiple recessive markers is patently homozygous. An interlaboratory study was performed in which 16 chemicals were tested under code in 2 laboratories. The results generated by the Berkeley and Darmstadt laboratories were in close agreement. Acetonitrile, ethyl acetate, 4-acetylpyridine, propionitrile and nocodazole were identified as potent inducers of mitotic chromosome loss. Acetone, dimethyl sulfoxide and 2-methoxyethyl acetate either elicited weak responses or yielded ambiguous results. Water, carbon tetrachloride, 4-fluoro-D,L-phenylalanine, amphotericin B, griseofulvin, cadmium chloride, ethyl methanesulfonate and methylmercury(II) chloride failed to induce chromosome loss. These data suggest that the system described herein represents a reliable assay for chemically induced chromosome loss in yeast.     

Nuclear-magnetic-resonance imaging of leaves ofMesembryanthemum crystallinum L. plants grown at high salinity

Differences in water binding were measured in the leaf cells ofMesembryanthemum crystallinum L. plants grown under high-salinity conditions by using nuclear-magnetic-resonance (NMR) imaging. The 7-Tesla proton NMR imaging system yielded a spatial resolution of 20·20·100 m³. Images recorded with different spin-echo times (4.4 ms to 18 ms) showed that the water concentrations in the bladder cells (located on the upper and lower leaf surface), in the mesophyll cells and in the water-conducting vessels were nearly identical. All of the water in the bladder cells and in the water-conducting vessels was found to be mobile, whilst part of the water in the mesophyll cells was bound. Patches of mesophyll cells could be identified which bound water more strongly than the surrounding mesophyll cells. Optical investigations of leaf cross-sections revealed two types of mesophyll cells of different sizes and chloroplast contents. It is therefore likely that in the small-sized mesophyll cells water is strongly bound. A long-term asymmetric water exchange between the mesophyll cells and the bladder cells during Crassulacean acid metabolism has been described in the literature. The high density of these mesophyll cells in the lower epidermis is a possible cause of this asymmetry.Abbreviations CAM Crassulacean acid metabolism - NMR nuclear magnetic resonance - T_E spin-echo time     

Role of phospholipase A2 in the stimulation of sponge cell proliferation by homologous lectin

Using the Geodia cydonium system, we showed that after incubation of competent sponge cells in the presence of lectin, phospholipase A2 was released from the cells. The substrates for this enzyme, phosphatidylethanolamine and phosphatidylcholine, were identified in the extracellular material of sponge tissue. In addition, the phospholipase A2 inhibitor calelectrin was identified by immunobiochemical techniques; this molecule was associated with the aggregation factor. Reconstitution experiments strongly suggested that phospholipase A2 catalyzed the release of arachidonic acid, which is then taken up by the cells. Intracellularly, arachidonic acid was metabolized primarily to prostaglandin E2. Inhibition studies revealed that prostaglandin E2 is involved in the ultimate increase of DNA synthesis. These findings suggest that the phospholipase A2-arachidonic acid system is involved in the matrix-initiated signal transduction pathway in sponges.