Basolateral membrane potassium conductance of A6 cells

Summary To study the properties of the basolateral membrane conductance of an amphibian epithelial cell line, we have adapted the technique of apical membrane selective permeabilization (Wills, N.K., Lewis, S.A., Eaton, D.C., 1979b, J. Membrane Biol. 45:81–108). Monolayers of A6 cells cultured on permeable supports were exposed to amphotericin B. The apical membrane was effectively permeabilized, while the high electrical resistance of the tight junctions and the ionic selectivity of the basolateral membrane were preserved. Thus the transepithelial current-voltage relation reflected mostly the properties of the basolateral membrane. Under basal conditions, the basolateral membrane conductance was inward rectifying, highly sensitive to barium but not to quinidine. After the induction of cell swelling either by adding chloride to the apical solution or by lowering the osmolarity of the basolateral solution, a large out-ward-rectifying K⁺ conductance was observed, and addition of barium or quinidine to the basolateral side inhibited, respectively, 82.4±1.9% and 90.9±1.0% of the transepithelial current at 0 mV. Barium block was voltage dependent; the half-inhibition constant (K _i) varied from 1499±97 m at 0 mV to 5.7±0.5 m at –120 mV.Cell swelling induces a large quinidine-sensitive K⁺ conductance, changing the inward-rectifying basolateral membrane conductance observed under basal conditions into a conductance with outward-rectifying properties.     

Plantlet regeneration from mesophyll protoplasts ofBetula platyphylla var.japonica

Summary InBetula platyphylla var.japonica, colonies were induced efficiently from mesophyll protoplasts cultured in half strength MS (1/2MS) liquid medium containing 0.6 M mannitol, 0.09M sucrose and 1 M 4-PU and 1 M NAA at a cell density of 5 × 10⁴/ml. The colonies grew actively and developed into callus after 3 months of culture.Roots differentiated from the protoplast-derived white calluses cultured on the 1 /2MS solid media supplemented with 0.1–1 M 4-PU and 1 M NAA, and 10 M zeatin with no supplementation of NAA. Furthermore, the protoplast-derived green callus differentiated shoots with 1/2MS solid medium containing 1 M 4-PU or 10 M zeatin with no supplementation of NAA. When shoots obtained were cultured on the cytokinin-free MS solid medium with 2.5 M IBA and 0.1 M NAA, they rooted and developed into plantlets after one month of culture.The phenylurea-type cytokinin, 4-PU, was effective for plantlet regeneration from the mesophyll protoplasts ofB. platyphylla var.japonica. This suggests that there is potential for the use of 4-PU in the culture of protoplasts in many forest tree species.Abbreviations BAP 6-benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - FDA fluorescein diacetate - IBA indole-3-butyric acid - 2ip N ⁶-(2-isopentenyl)-adenine - NAA 1-naphthaleneacetic acid - 4-PU N-(2-chloro-4-pyridyl)-N–phenylurea - TDZ thidiazuron     

Osmotic measurements on stomatal cells ofCommelina communis L.

Summary Observations of aperture changes as sucrose is added to the solution bathing epidermal strips ofCommelina communis L. allow calculation of the osmotic changes required to open or close the stomatal pore, for comparison with changes in potassium content. With isolated guard cells, in strips in which all cells other than guard cells have been killed, the internal osmotic changes required are 83 mosmol kg^–1 m^–1 below 10m aperture, 129 mosmol kg^–1 m^–1 in the range 10–15 m, and 180 mosmol kg^–1 m^–1 above 15 m. For opening against subsidiary cell turgor in addition to guard cell turgor, in intact strips with live subsidiary and epidermal cells, these figures should each be increased by about 33 mosmol kg^–1 m^–1. A change in subsidiary cell turgor is magnified in its effects on the water relations of the guard cell by a factor greater than 3.7 for equal changes in the water potential of the two cells, or greater than 4.7 at constant volume of the guard cell.     

Studies on the morphology and taxonomy of three new myxosporeans of the genus Sinuolinea Davis, 1917 (Myxosporea: Sinuolineidae) infecting the urinary bladder of some marine fishes from the Shandong coast,China

The morphology and taxonomy of three new species of myxosporeans (Myxosporea: Sinuolineidae), Sinuolinea shandongensis n. sp., S. argyrosomi n. sp. and S. platycephali n. sp., parasitising marine fishes collected from the Yellow Sea off the coast of southeast Shandong, China, were investigated. These species, including spores and plasmodia, were found in the urinary bladder of their hosts. The diagnostic features of the new species are as follows. S. shandongensis n. sp. from Nibea albiflora: monosporous and disporous plasmodia, 29–37 × 29–27 m; spore inversely pyramidal or spherical, with smooth surface and fine, highly sinuous sutural line, 16.4±2.4 (15–20) × 16.1±1.1 (15–18) m; two spherical polar capsules located anteriorly and conspicuously separated from each other, 4.8±0.3 (4.5–5.5) m in diameter; length of polar filament 59–61 m; coelozoic. S. argyrosomi n. sp. from Argyrosomus argentatus: monosporous plasmodium, (33–42) × (24–25) m; spore subspherical to spherical, with smooth surface and highly sinuous sutural line, 18.1±1.0 (17–20) × 19.8±1.3 (18–22) m; two spherical polar capsules located anteriorly and conspicuously separated from each other, 4.4±0.2 (4–5) m in diameter; length of polar filament 47–50 m; coelozoic. S. platycephali n. sp. from Platycephalus indicus: monosporous, disporous and polyporous plasmodia, 25–42 × 17–31 m; spore spherical with smooth surface and highly sinuous sutural line, 14.5±0.5 (14–15) m in diameter; two spherical polar capsules located anteriorly and conspicuously separated from each other, 4.3±0.2 (4–4.5) m in diameter; coelozoic.     

The use of antimicrotubule herbicides for the production of doubled haploid plants from anther-derived maize callus

Summary Four antimicrotubule herbicides, amiprophosmethyl (APM), pronamide, oryzalin, and trifluralin, were evaluated for their ability to induce chromosome doubling in anther-derived, haploid maize callus. Effects of various herbicide treatments on the growth and regenerative capacity of callus along with the ploidy and seed set of regenerated plants were determined. Flow cytometric analysis was also used to measure changes in ploidy levels of callus cells following treatments. More than 50% of the cells were doubled in chromosome number after the haploid callus was treated with 5 or 10 M APM or 10 M pronamide for 3 days. A similar proportion of plants regenerated from the treated callus produced seed upon self-pollination. APM and pronamide did not inhibit callus growth at these concentrations and the treated callus retained a high plant regeneration capacity. Oryzalin very effectively induced chromosome doubling, but severely inhibited the growth of regenerable callus and plant regeneration. Trifluralin induced chromosome doubling in a small proportion of cells at lower concentrations (0.5 and 1 M), however, at a higher concentration (5 M) it inhibited callus growth and plant regeneration. The results indicate that APM and pronamide may be useful agents for inducing chromosome doubling of anther-derived maize haploid callus at very low concentrations.     

Circular and linear structures in chromatin diminution of Cyclops

In confirmation of earlier findings, surface-spread early diminution stages of Cyclops furcifer and C. divulsus yield numerous chromatin rings formed by the 25-to 30-nm type of fiber. Their contour lengths have a range of 0.6 16 m in C. divulsus and 0.4–40 m in C. furcifer. Employing the Miller spreading technique nucleosomal chromatin rings were detected in the critical stages of diminution in a size range of 0.6–100 m, though in lower frequencies. Instead, linear fragments of nucleosomal chromatin were found in numbers equal to or surpassing that of the rings.     

The chromosome idiogram of Nicotiana plumbaginifolia

The karyotype of Nicotiana plumbaginifolia (2n=20) was determined by the analysis of 25 metaphase plates of both haploid and diploid plantlets. The material originated from root tip meristems and leaf protoplasts. Chromosome length ranged from 1.73 to 4.34 m and the total length of the genome was 30.2 m. The following chromosome pairs have been recognized: three metacentrics, two submetacentrics, one subtelocentric, one subtelocentric with satellites and three telocentrics.Contribution no 2036 of the Biology, Radiation protection and Medical Research Programme, Directorate General XII of the Commission of the European Communities.     

Microbial decolorization of azo dyes and dye industry effluent by Fomes lividus

The white rot fungus, Fomes lividus, was isolated from the logs of Shorea robusta in the Western Ghats region of Tamil Nadu, India. The fungus was tested for decolorization of azo dyes such as orange G (50 M) congo red (50 M) amido black 10B (25 M) and also for colour removal from dye industry effluents. The results revealed that the fungus could remove only 30.8% of orange G in the synthetic solution, whereas congo red and amido black 10B were removed by 74.0 and 98.9% respectively. A dye industry effluent was treated by the fungus in batch and continuous mode. In batch mode treatment, a maximum decolorization of 84.4% was achieved on day 4, and in continuous mode a maximum decolorization of 37.5% was obtained on day 5. The colour removal by the basidiomycete fungus might be due to adsorption of the dyes to the mycelial surface and metabolic breakdown. These results suggested that the batch mode treatment of Fomes lividus is one of the most efficient ways for colour removal in dye industry effluents.     

Thermoproteus uzoniensis sp. nov., a new extremely thermophilic archaebacterium from Kamchatka continental hot springs

A new extremely thermophilic rod-shaped archaebacterium was found in the samples from hot springs and soil of the Uzon caldera (SW of Kamchatka pen.). Cells are rods from 1 to 20 m in length and 0.3 to 0.4 m in width, sometimes branching or with spherical protrusions on the ends. The cell wall consists of two layers: an internal one with distinct hexagonal structure and the outer one with less clear structure and variable thickness. Cells are non-motile and have no flagella. The new organism grows anaerobically by fermenting peptides, concurrently reducing elemental sulfur to H₂S. Fermentation products are acetate, isobutyrate, isovalerate. The G+C content of the DNA is 56.5 mol. %. A new species Thermoproteus uzoniensis is described. Type strain is isolate Z-605, DSM 5262.     

Distance-constraint approach to protein folding. I. Statistical analysis of protein conformations in terms of distances between residues

A statistical analysis of protein conformations in terms of the distance between residues, represented by their C atoms, is presented. We consider four factors that contribute to the determination of the distanced _i,i+k between a given pair ofith and(i+k)th residues in the native conformation of a globular protein: (1) the distancek along the chain, (2) the size of the protein, (3) the conformational states of theith to(i+k)th residues, and (4) the amino acid types of the and(i+k)th residues. In order to account for the dependence on the distancek along the chain, the statistics are taken for three ranges, viz., short, medium, and long ranges (k8; 9k20; andk21; respectively). In the statistics of short-range distances, a mean distanceD _k and its standard deviationS _k are calculated for each value ofk, with and without taking into account the conformational states of all residues fromi toi+k (factors 1 and 3). As an Appendix, the relations for converting from the distances between residues into other conformational parameters are discussed. In the statistics of long-range distances, a reduced distanced* _ij (the actual distance divided by the radius of gyration) is used to scale the data so that they become independent of protein size, and then a mean reduced distanceD _l (a, a) and its standard deviation _l (a, a) are calculated for each amino acid pair (a, a) (factors 2 and 4). The effect of the neighboring residues along the chain on the value of the distanced* _ij is explored by a linear regression analysis between the actual reduced distanced* _ij and the mean value over theD _l for all possible pairs of residues in the two segments of the (i–2)th to the (i+2)th and the (j–2)th to the (j+2)th residues. The effect is assessed in terms of the tangentA _l (a, a) of the calculated regression line for each amino acid pair (a, a). In the statistics of medium-range distances, only factors 1 and 4 are considered, to simplify the analysis. The scaled distanced _i,i+k =(d _i,i+k -D _k )/S _k is used to eliminate the dependence onk, the distance along the chain. The propertiesD _m (a, a), _m (a, a) andA _m (a, a) corresponding toD _l (a, a), _l (a, a), andA _l (a, a), and also calculated for each amino acid pair (a, a). The results are interpreted as follows: the smaller values ofD _l (a, a) andD _m (a, a) indicate a preference of the pair (a, a) for a contact (e.g., pairs between hydrophobic amino acids, and pairs of Cys with aromatic amino acids), and the larger values of these quantities indicate a preference for distant mutual location (e.g., pairs between strong hydrophilic amino acids); the smaller values of _l (a, a) and _m (a, a) indicate a strong preference for either contact or noncontact (e.g., pairs between hydrophobic amino acids, and pairs between strong hydrophobic and hydrophilic amino acids, respectively), and the larger values of these quantities indicate the ambivalent/neutral nature of the preference for contact and noncontact (e.g., pairs containing Ser or Thr); the smaller values ofA _l (a, a) andA _m (a, a) indicate that the distance of an (a, a) pair is determined independently of the amino acid character of the neighboring residues along the chain (e.g., some pairs of Cys or Met with other amino acids) and the larger values of these quantities indicare that such amino acid character contributes strongly to the determination of the distance (e.g., pairs containing Ser or Thr, and pairs between amino acids with small side chains). The difference between the statistics for the long- and medium-range distances is also discussed; the former reflect the difference between the hydrophobic and hydrophilic character of the residues, but the latter cannot be easily interpretable only in terms of hydrophobicity and hydrophilicity. The data analyzed here are used in the optimization of an object function to compute protein conformation in a subsequent paper.     

Micropropagation of flowering dogwood (Cornus florida) from seedlings

A method for regenerating whole plants from nodal (axillary bud) cultures of seedlings was developed for flowering dogwood (Cornus florida L.). The seed source significantly influenced the rate of proliferation, although cultures initiated from each of the seven mother trees produced some shoots. Woody plant medium (WPM) was superior to either Murashige and Skoog or Schenk and Hildebrandt basal medium. 6-Benzyladenine (BA) at 2.2 or 4.4 m stimulated the generation of significantly more useable shoots (1 cm) compared to all other concentrations (0.5–22.5 m tested. Thidiazuron (TDZ) at 0.6 and 1.1 m supported proliferation, but strongly inhibited shoot elongation. TDZ initiated cultures transferred to medium containing 4.4 m BA produced usable shoots after five additional subcultures. Shoots generated adventitious roots when exposed to either a 12-h pulse of relatively high concentrations (246–1230 m or continuous lower concentrations (0.5–49.0 m of indolebutyric acid (IBA) for longer periods. Microshoots produced the significantly greatest number of roots when subjected to 4.9 m IBA in WPM over a 4-week period. Whole plants were acclimatized to the laboratory conditions and subsequently to the greenhouse. The methodology described here should be useful in a breeding program by supplying multiple copies of unique, recombinant genotypes.     

Retinoic acid causes the development of feathers in the scale-forming integument of the chick embryo

Summary Injection of retinoic acid (3×62.5 g or 3×125 g) into the amniotic sac of chick embryos between 10 and 12 days of incubation resulted in the formation of club-shaped feathers within the feather tracts, and the development of feathers in the scale-forming areas of the feet. The latter finding is interpreted as caused by a disturbance of the tissue interactions which occur in the skin of the feet at this time. The address for correspondence: Universitè Scientifique et Médicale de Grepoble, Laboratoire de Zoologie et Biologie animale, Boîte Postale n^o 53-Centre de Tri, F-38041 Grenoble Cedex, France     

A new myxosporean,Zschokkella leptatherinae n. sp. (Myxozoa: Myxidiidae), from the hepatic ducts and gall-bladder of Australian marine fishes

A new myxosporean,Zschokkella leptatherinae n. sp., was found in the hepatic ducts and gall bladder of five atherinid fish species,Leptatherina presbyteroides, Atherinosoma microstoma, Kestratherina brevirostris, K. esox andK. hepsetoides, collected at Dru Point, Margate in south-eastern Tasmania, Australia. This species has a round, ellipsoid or irregular plasmodium. The plasmodium is enclosed by a surface membrane and the cytoplasm is composed of an outer homogeneous ectoplasm and an inner coarse endoplasm with large clear areas, numerous vacuoles and spores which differentiate in the central area of the endoplasm. The characteristic metrical data of the myxosporean are as follows: spores 15.3 × 11.8 m; polar capsules 3.9 × 3.4 m. This is the thirdZschokkella species reported from Australia.     

Five new species of Eimeria (Apicomplexa: Eimeriidae) from lizards

Five new species of Eimeria are described from lizards. Eimeria baltrocki n. sp. was found in the berber skink, Eumeces schneideri, from Egypt. The oöcysts are cylindroidal, averaging 38 × 18.3 m, with a single thick oöcyst wall. Most oöcysts possess a single polar granule; a micropyle and oöcyst residuum are absent. The sporocysts are ellipsoidal and average 11.5 × 8.1 m, each with a large, globular sporocyst residuum; the Stieda body is absent. Eimeria anolidis n. sp. is described form the common anole, Anolis carolinensis, from Florida, USA. The oöcysts are cylindroidal and average 31 × 15.8 m with a thick, single-layered oöcyst wall. Two polar granules are usually present; a micropyle and oöcyst residuum absent. The sporocysts are ellipsoidal and average 9.4 × 7.5 m with a globular sporocyst residuum; the Stieda body is absent. Eimeria guyanensis n. sp is recorded in the ameiva, Ameiva ameiva, from Guyana, South America. The oöcysts are spherical to subspherical, average 19.0 × 17.8 m and possess a thick, single-layered oöcyst wall. Numerous polar granules are present (n > 5); a micropyle and oöcyst residuum are absent. The sporocysts are spherical to subspherical, average 7.5 × 7.8 m and possess a compact globular sporocyst residuum; the Stieda body is absent. Eimeria phelsumae n. sp. was recovered from the giant day gecko, Phelsuma madagascariensis grandis, from Madagascar, which harboured a simultaneous infection of E. brygooi. The oöcysts measured 32 × 15 m and are cylindroidal without polar granules, a micropyle or oöcyst residuum, or a Steida body. The sporocysts are ellipsoidal and average 9.8 × 7 m, with a loosely clumped, granular sporocyst residuum; the Steida body is absent. Eimeria leiocephali n. sp. was discovered in the faeces of the ornate ground iguana, Leiocephalus barahonensis, from Haiti. The oöcysts are spherical to subspherical, 21 × 19 m, and contain a number of polar granules (n > 5); a micropyle and oöcyst residuum are absent. The sporocysts are spherical, 8 m in diameter and lack a sporocyst residuum. Eimeria turcicus and E. lineri were found in faeces of Hemidactylus turcicus turcicus from the host's country of origin, Turkey.     

Isospora lutrae n. sp. (Apicomplexa: Eimeriidae), a new coccidium from the European otter Lutra lutra (L.) (Carnivora: Mustelidae) from Spain

Parasitological examination of European otter originating from Extremadura, Spain revealed the presence of a new isosporan species. Oöcysts of Isospora lutrae n. sp. are spherical to subspherical, 31.2 (27.5–32) × 29.6 (28–31) m and have a smooth wall c. 1 m thick. Sporocysts are ellipsoidal, 18.2 (17–19) × 14.4 (14–16) m and lack Stieda and substieda bodies. A spherical sporocyst residuum is present, consisting of granules scattered among the sporozoites. Sporozoites are spindle-shaped, 12.4 × 2.5 m and have anterior and posterior refractile bodies. Based on its unique morphologic structure and host, I. lutrae is considered to be new.     

Long-term investigation of the degree of exposure of German peregrine falcons ( Falco peregrinus) to damaging chemicals from the environment

The contamination of German peregrine falcons (Falco peregrinus) with organochlorine (CHC) biocides and mercury (Hg) was investigated over the years 1955–2002. A total of 960 unhatched eggs from eastern Germany, Baden-Württemberg (BW) and North Rhine-Westphalia/Rhineland Palatinate (NRW/RP) were analysed for the biocides DDE, HCB, PCB, etc., and for shell index and shell thickness. Hg analyses from 367 samples (unhatched eggs, moulted and nestling feathers, tissue samples) complete the investigation. The results confirm that the collapse of the German peregrine populations is correlated with the application of the insecticide DDT. The mean DDE values in BW over the years 1970–1976 were above the relevant threshold values of 70–100 g/g (all concentrations refer to the dry sample mass), with single analyses showing values above 100 g/g until as late as 1987. The mean contamination levels in the 1960s can be retrospectively assumed to have lain above 200 g/g. With the help of thorough conservation measures it was possible after a fall in numbers of about 80% to stabilise the remnant population in BW . Following the West German DDT ban in 1972 and the resulting decline in environmental CHC contamination, this core population was able to recover from about 1980 onwards and has since increased tenfold. The shell index improved steadily from 1.48 (1970–1971) to a normal value of 1.80–1.88 (2000–2002). Hg contamination in western Germany stayed under toxic threshold values over the period 1969–1991. The significantly more intense application of DDT in eastern Germany, continuing until 1989, led to the extinction of the peregrine falcon, of both the cliff- and tree-nesting populations. This phenomenon is described with respect to DDE analysis data and shell thickness/index studies, complemented by observations of breeding biology. In addition, the employment in the GDR of methyl/phenyl Hg as seed treatments had dramatic local toxic effects on embryo survival and shell thickness. Hg burdens reached very high levels in feathers (147 µg/g) and eggs (65 g/g). The combination of DDT and Hg was responsible for the species extinction in this region. The current peregrine falcon population of eastern Germany even now shows biocide contaminant burdens up to 3 times higher than in samples from western German falcons. Shell index and shell thickness had, however, normalised to a large extent by 2002. The tree-nesting habit of the peregrines formerly breeding in the forested lowlands of Central and Eastern Europe, a tradition which had been passed on by imprinting, has been completely eradicated as a result of the effects of the environmental contamination. In NRW/RP unhatched eggs over the period 1989–2002 show uncritical DDE contamination levels in the region of 4–20 g/g with normal shell index values. PCB analyses from all three regions confirm the highest levels of contamination from industrial centres with no clear trend so far. HCB burdens peaked at a maximum of 80 g/g and have been stable at <1 g/g since 1983. Population parameters did not improve in BW until 1976, after DDE and HCB contamination levels had started to decrease as a result of the bans on use. In East Germany and NRW/RP, the documented recolonisation and increases in breeding success parameters were only possible after the DDE levels (and in East Germany additionally the Hg levels) had fallen to below toxic threshold levels.Communicated by F. Bairlein     

The endogenous development of three new intranuclear species of Isospora (Apicomplexa: Eimeriidae) from agamid lizards

Three new species of Isospora Schneider, 1881 are described from agamid lizards, Isospora cannoni n. sp. in Diporiphora australis from northern Queensland, Australia, I. choochotei n. sp. in Calotes mystaceus from northern Thailand, and I. deserti n. sp. in Agama pallida from Israel. I. cannoni oöcysts are subspherical, 20–25 × 22.5–27.5 m with two ovoid sporocysts, 14–15.5 × 10–11.5 m. I. choochotei oöcysts are spherical to subspherical, 24–32 × 28–32.5 m with two ovoid sporocysts, 11 × 15.5–18 m. I. deserti oöcysts are spherical, 25–28 m in diameter with two ovoid sporocysts, 10–11 × 14–17.5 m. All species had sporocysts with Stieda bodies and underwent endogenous development in the nucleus of the host gut epithelial cells. At completion of merogony and gamogony, the host nucleus was reduced to a thin envelope. The significance of endogenous stage characteristics in Isospora taxonomy is discussed.     

Structural and histochemical characterization of the cotyledon storage organelles of jojoba (Simmondsia chinensis)

Summary Jojoba cotyledon cells are isodiametric and 44 m in diameter. They contain two prominent storage organelles—wax bodies and protein bodies. Isolated and intact wax bodies react positively with several lipid histochemical stains; they are spherical and 1.5 m in diameter. Protein bodies are irregular in shape, but usually appear spherical. They range in diameter from 7–15 m, are unit membrane bound, have an irregular grainy matrix and do not contain a globoid inclusion. Protein bodies stain positively for both protein and lipid. The possible composition and role of this protein/lipid body complex is discussed.     

Growth and physiology of potassium-limited chemostat cultures of Paracoccus denitrificans

In potassium-limited chemostat cultures of Paracoccus denitrificans the maximum specific growth rate (µ_max) was found to depend on the input potassium concentration: At 0.21mM µ_max was 0.10–0.11 h^-1; at 0.44 mM 0.15–0.16 h^-1 and at 0.66 mM 0.20–0.21 h^-1. The plots of the specific rates of oxygen-, succinate-and potassium consumption against gave straight lines. The intracellular potassium concentration was a linear function of and varied from 1% (0.13 M) at a value of 0.034 h^-1 to 2.2% (0.29 M) at =0.26 h^-1; the potassium concentration gradient and the potassium concentration in the culture fluid in the steady state were dependent on the input potassium concentration. The potassium concentration gradient varied from 8,900-1,200. At all values 20–25% of the total energy production was used for potassium transport. 350,100 and 30 ATP molecules were calculated to be required to maintain one potassium ion intracellular during 1 h at values of 0.034, 0.197 and 0.257 h^-1 respectively. It is concluded that the amount of circulation of potassium is dependent on the potassium concentration gradient or on the potassium concentration in the culture in the steady state. The dependency of µ_max on the input potassium concentration was explained by the assumption that at low input potassium concentrations the net uptake of potassium (influx-efflux) is not rapidly enough to maintain the high potassium gradient in the existing cells and to establish it in the newly formed cells. At high values and at high input potassium concentrations µ_max is limited by the specific rate of oxygen consumption, which was found to be 11–12 mmol O₂ g dry weight^-1 h^-1 at µ_max for potassium-, succinate-and sulphate-limited chemostat cultures.     

Adventitious shoot regeneration from leaf explants of tissue cultured and greenhouse-grown raspberry

Adventitious shoot regeneration was observed using leaf-petiole explants from shoot-proliferating cultures of Comet red raspberry (Rubus idaeus L.). A maximum regeneration rate of 70% (3.7 shoots/explant) was obtained using 4.5–9.1 M (1–2 mg l^–1) N-phenyl-N-1,2,3-thiadiazol-5-ylurea (thidiazuron or TDZ) with 2.5–4.9 M (0.5–1 mg l^–1) 1H-indole-3-butanoic acid (IBA) or 2.3 M (0.5 mg l^–1) TDZ with 4.9 M (1 mg l^–1) IBA in modified Murashige-Skoog medium. TDZ was more effective than N-(phenylmethyl)-1H-purin-6-amine (BA) at promoting regeneration in combinations tested with IBA (maximum 50% regeneration rate; 1.8 shoots/explant). Variation in the agar concentration or incubation temperature, orientation or scoring of the leaf-petiole explants and use of separate leaf or petiole explants had no effect on shoot regeneration. Incubation in the dark for 1, 2 or 3 weeks prior to growth in the light did not influence the percent regeneration rate but depressed the number of adventitious shoots. Explant source, from micropropagated shoots or greenhouse-grown plants, had an effect on shoot regeneration that was genotype dependent. Only 8 of 22 (36%) raspberry cultivars were capable of regeneration from leaf explants derived from greenhouse-grown plants.