Concentration and shear rate dependence of viscosity in random coil polysaccharide solutions

The concentration (c) and shear rate (γ) dependence of viscosity (η) has been studied for a wide range of random coil polysaccharide solutions, and the following striking generalities are observed:

1. 1. The transition from dilute to concentrated solution behaviour occurs at a critical concentration , when ‘zero shear’ specific viscosity (η_sp) ≈ 10. η_sp varies as c^1.4 for dilute solutions, and as c^3.3 for concentrated solutions.

2. 2. The shear rate dependence of viscosity, and frequency dependence of dynamic (oscillatory) viscosity are closely superimposable.

3. 3. Double logarithmic plots of against (where η₀ is ‘zero shear’ viscosity, and is the shear rate at which ) are essentially identical for all concentrated solutions studied, and thus the two parameters η₀ and completely define the viscosity at all shear rates of practical importance.

Departures from points 1 and 2, but not 3, are observed for concentrated solutions of locust bean gum, guar gum, and hyaluronate at low pH and high ionic strength and are attributed to specific intermolecular associations (‘hyperentanglements’) of longer timescale than non-specific physical entanglements.     

Topography of substrate-attached glycoproteins from normal and virus-transformed cells

The topographical distribution of substrate-attached material (SAM) which may mediate adhesion of BALB/c 3T3 and SV40-transformed 3T3 cells to the culture substrate has been examined at both the macroscopic and microscopic levels. Autoradiographic detection of these ‘glycoproteins’ on the substrate subsequent to incorporation of ¹⁴C-glucosamine or ³⁵S-methionine and exposure to X-ray film indicated:

1. 1. Evenly distributed glucosamine-labeled SAM on the substrate of confluent cultures.

2. 2. A deficiency in the methionine content of SAM from transformed cells.

3. 3. Direct deposition of these materials onto the substrate at cell colony locations, and not randomly on the substrate subsequent to secretion into the medium.

Autoradiographic detection of these ‘glycoproteins’ subsequent to ³H-glucosamine (or ³H-leucine) incorporation and exposure to liquid emulsion indicated:

1. 1. Substrate-attached glycoproteins are present in focal pools on the underside of the cell.

2. 2. These focal pools are distributed comparably, in terms of number of foci per area of substrate, for confluent normal and transformed cells. The patterns of SAM deposited by freshly-attaching and spreading 3T3 cells has also been examined. The evidence suggests that cells are adherent to the substrate at localized areas which appear to be evenly distributed on the underside of normal or transformed cells.

     

Kitchen hygiene in daily life

More and more data are available indicating that numerous (infectious) diseases are related to the home environment. Airborne microorganisms (bacteria, fungi), mites (in sheets or carpets), and (parts of) insects and beetles may be the cause of respiratory diseases such as asthma. In Europe and North America, more than half of the registered food infections appear to be contracted in the home. Then there is the development of new pathogens or the adaptation of microorganisms to extreme conditions. In many cases, the occurrence of adapted or resistant microorganisms is a reaction to the changing environment. Examples of this are the growth of Listeria monocytogenes in refrigerated food products and the presence of Legionella pneumophila in systems containing stagnant water.The main sources of infection in the domestic environment are people, pests, pets, and contaminated food and water. Germs are transmitted by direct contact with people or animals, by contaminated food, water, surfaces and air.Under circumstances favourable to microorganisms, the cells are able to survive or multiply into large numbers. Especially in places which stay moist for a long time considerable amounts of microorganisms are found, among with pathogenic types.The phrase ‘home hygiene’ does not merely refer to cleaning the house (daily). In practice, cleaning is not the only important issue; knowing how to prevent contamination is just as crucial. Domestic hygiene is the total sum of the measures used to prevent (insofar as possible) contamination with pathogens, and thus decreasing the number of infectious diseases. The hygiene measures required can be divided into three groups:

• Hygiene during food preparation.

• Personal and sanitary hygiene.

• Domestic environment.

This contribution will focus on food storage, food preparation and the effect of 'hygienic cleaners’ in the domestic kitchen.     

Bovine lens epithelium: A suitable model for studying growth control mechanisms : C6-substituted purines inhibit cell flattening and growth stimulation of G0 cells

1. 1. The resting lens epithelium of adult bovines has been used for the study of early events during stimulation to mitotic growth in primary culture. This system offers special advantages, since it consists of a pure population of ‘anchorage dependent’ epithelial cells with more than 99% of the cells in G0.

2. 2. Retraction of the cell sheet as well as respreading and cell flattening are characteristic phenomena of locomotion preceding the inception of DNA synthesis in primary culture.

3. 3. Sheet retraction has been characterized as an active, ATP-dependent process requiring both intact microfilaments and extracellular calcium.

4. 4. The early phase of respreading is dependent on neither intact microfilaments nor microtubules, but is specifically inhibited by adenine, hypoxanthine, guanine, adenosine, AMP and cAMP. Calcium uptake experiments reveal that these purine derivatives reduce the uptake of extracellular calcium which is suggested to be the virtual primary mitotic stimulator for resting lens cells.

5. 5. A conspicuous correlation does exist between the calcium depressing specificity of the purine derivatives, their well known capacity to depress the level of cellular phosphoribosylpyrophosphate (PRPP) and their ability to retard cell flattening.

6. 6. The calcium-depressing action of the purines has been suggested to be partially responsible for their PRPP-depressing capacity and it is concluded that both calcium and PRPP might be involved in the activation process of ‘anchorage dependent’ resting lens cells.

     

The use of fluorescein-conjugated Bandeiraea simplicifolia B4-isolectin as a histochemical reagent for the detection of α- -galactopyranosyl groups : Their occurrence in basement membranes

The Bandeiraea simplicifolia B₄-isolectin, which combines specifically with α- -galactopyranosyl groups, has been conjugated with fluorescein isothiocyanate and demonstrated to be a reliable histochemical probe for the detection of these groups in normal tissues of mouse, rabbit, rat and man. Specificity of binding of the fluorescein-conjugated B. simplicifolia B₄-isolectin to native cryostat tissue sections was demonstrated in two ways:

1. 1. The hapten inhibitor methyl α- -galactopyranoside prevented the binding of the lectin to tissues whereas the non-hapten methyl α- -glucopyranoside did not.

2. 2. Pretreatment of tissue sections with coffee bean α-galactoside abolished lectin binding whereas pretreatment with A. niger or E. coli β-galactosidase did not. The fluorescein-conjugated isolectin visualized α- -galactopyranosyl groups in basement membranes and on the surface of certain epithelial cells of mouse, rat, rabbit, and on the surface of the TA3 murine mammary carcinoma. These studies suggest that the B. simplicifolia B₄-isolectin may be of great utility in studying the family of α- -galactosyl-containing glycoconjugates of basement membranes in pathological states accompanied by basement membrane changes, such as diabetes mellitus, and in neoplasms that secrete basement membrane.

     

The effects of cell-cell contact on the spreading of pigmented retina epithelial cells in culture

The behaviour of chick embryo pigmented retina epithelial (PRE) cells has been studied in living and fixed cultures. Isolated PRE cells lacking contacts with other cells were characteristically only poorly spread upon the substrate, blebbed vigorously and lacked leading lamellae. PRE cells incorporated into islands or sheets of cells were extensively spread upon the substrate, lacked blebs and displayed typical leading lamellae if marginally positioned in an island. Observations of living cultures demonstrated that within 3 h of establishing contact with an island of cells a previously isolated PRE cell lost the morphology characteristic of isolated cells and became indistinguishable from its neighbours in the island. Measurements of the area of substrate occupied by single cells and cells in 2-cell islands suggests that similar changes occur as two cells make contact to form a 2-cell island. The evidence suggests that these changes are a direct response to the establishment of a cell-cell contact and I propose that the phenomenon be termed ‘contact-induced spreading’.Contact-induced spreading is not an ‘all or none’ phenomenon since isolated PRE cells can spread extensively and cease blebbing in the absence of cell contact. However a given isolated PRE cell spends only a very small proportion of its time displaying this well spread morphology and therefore at any time the majority of isolated PRE cells display the poorly spread morphology.The possible relationship between contact-induced spreading and other cellular interactions known to be dependent on cell-cell contact is discussed.     

Interactions of cardiac glycosides with cells and membranes Properties and structural aspects of two receptor sites for ouabain in erythrocytes

The existence of two types of binding sites for ouabain in human erythrocyte membranes is described. Receptor sites designated as ‘type I’, which may be identical to the K⁺-insensitive sites of intact cells, were detected at concentrations of ouabain as low as 10⁻⁷ M. The ‘type II’ receptor sites require the inclusion of Mg²⁺ + P_i to form complexes with ouabain; they may be identical to the K⁺-sensitive sites of intact cells. These sites were saturated at approx. 5 · 10⁻⁷ M ouabain but could not be detected at higher concentrations. The range of ouabain concentrations at which ‘type I’ receptors start to predominate (i.e. 5 · 10⁻⁸–5 · 10⁻⁷ M) was termed ‘critical digitalis concentrations’. The process of binding reached equilibrium within 1 and 4 h for ‘type I’ and ‘type II’ sites, respectively. The dissociation constant for ‘type II’ receptor-ouabain complexes was 7.6 · 10⁻⁹ M.Under similar experimental conditions, rat erythrocyte membranes exhibited only non-saturable sites.Alterations in the proportions of the two types of receptors were demonstrated by preincubation of the membranes, in the presence or absence of Mg²⁺ + P_i, prior to the addition of ouabain. In the first case, ‘type II receptor-ouabain’ complexes were stabilized at about 50% of the untreated membranes and ‘type I-ouabain’ complexes slowly approached equilibrium over a period of 24 h. In the latter instance, ‘type I’ receptors were not detected, and only ‘type II-ouabain’ complexes prevailed.     

Induction of a reversible G 1 block in human glia-like cells by cytochalasin B

In cultures of normal adult human glia-like cells, density-dependent cell cycle inhibition (topoinhibition) and contact inhibition of ruffling occur almost simultaneously, suggesting a functional coupling between activities of the cell surface and the initiation of DNA synthesis. The present paper examines whether cytochalasin B (CB), which reversibly inhibits ruffling, also blocks the glia cell cycle.The effects of the drug (2 μg/ml) were the following:

1. 1. Initiation of DNA synthesis of subcultivated stationary cells was inhibited.

2. 2. Stimulation of DNA synthesis in stationary cells by medium change was suppressed.

3. 3. Migration of cells into a wound in a confluent cell layer was blocked as well as the initiation of DNA synthesis in cells lining the wound.

4. 4. Initiation (but not continuation) of DNA synthesis of exponentially growing cells was inhibited leading to a population mainly arrested in G 1 as determined by microspectrophotometry on Feulgen-stained cells. Topoinhibited cells were also blocked in G 1. Since cytokinesis was blocked by CB, a fraction of binuclear cells appeared.

The cell cycle block induced by CB was reversible, even after several weeks of treatment, with the exception that binuclear cells more reluctantly entered the S phase after release of the block.In conclusion, CB efficiently induces a reversible and probably physiologic cell cycle block. This finding strengthens the notion of a connection between cell membrane and cell proliferation. The underlying mechanism is discussed.     

Gibberellic acid impairs fertilization in Clementine mandarin under cross-pollination conditions

We investigated the effect of gibberellic acid (GA₃) in the fertilization of Clementine mandarin cv. ‘Clemenules’ (Citrus clementina Hort. ex Tan.), a parthenocarpic variety that produces seedless fruit due to its self-incompatible nature, but yields seedy fruits when grown under cross-pollination conditions.Experiments were conducted with on-tree ‘Clemenules’ flowers and ‘Fortune’ mandarin pollen (C. clementina Hort. ex Tan. × C. reticulata Blanco), which is sexually compatible with the former. Preanthesis treatment at −2 days after anthesis (−2 DAA) enhanced ovule abortion in both unpollinated and cross-pollinated (at +2 DAA) flowers. In the latter, the number of pollen tubes reaching the ovules was significantly reduced although pollen grains were not treated; thus, fertilization was partially avoided and seed set was reduced. When GA₃ was applied at anthesis (0 DAA) at the time of pollination, ovule abortion was again enhanced, and pollen tube growth was completely arrested; thus, fertilization was prevented and seed set was impeded. When GA₃ was applied 24 h after pollination (+1 DAA in flowers pollinated at anthesis), pollen tube growth was impaired but not arrested and ovule abortion was enhanced; therefore, fertilization was not prevented but impaired.We conclude that, when applied the days around anthesis, GA₃ (10 mg l⁻¹) impairs fertilization by either enhancing ovule abortion or reducing pollen tube growth, in ‘Clemenules’ flowers under cross-pollination conditions. The intensity of the response depends on the physiological flower state at the moment of treatment.     

Oxidative stress,antioxidant activity and Fe(III)-chelate reductase activity of five <Emphasis Type="Italic">Prunus</Emphasis> rootstocks explants in response to Fe deficiency

The aim of this work was to investigate whether Fe reduction and antioxidant mechanisms were expressed differently in five Prunus rootstocks (‘Peach seedling,’ ‘Barrier,’ ‘Cadaman,’ ‘Saint Julien 655/2’ and ‘GF-677’). These rootstocks differ in their tolerance to Fe deficiency when grown in the absence of Fe (−Fe) or in presence of bicarbonate (supplied as 5 or 10 mM NaHCO₃). Fe deficiency conditions, especially bicarbonate, were shown to decrease Fe and total chlorophyll (CHL) concentration. In the (−Fe)-treated roots of all rootstocks and in the 5 mM NaHCO₃-treated ones of the tolerant ‘GF-677’ the Fe(III)-chelate reductase (FCR) activity was stimulated. On the contrary, apart from the ‘GF-677,’ FCR activity was greatly inhibited by the 10 mM NaHCO₃. From the results obtained with decapitated rootstocks, it is not entirely clear whether or not the presence of shoot apex was a prerequisite to induce FCR function in all rootstocks tested. In the leaves of rootstocks exposed to the (−Fe) treatment, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were enhanced whereas the levels of the non-enzymatic antioxidants (FRAP values) were increased in the Fe-deprived leaves, irrespective of the rootstock. Except for ‘Peach seedling,’ foliar SOD activity was stimulated by the presence of NaHCO₃. Furthermore, POD activity was increased in the ‘Saint Julien 655/2’ and ‘GF-677,’ but was depressed in the ‘Barrier’ rootstocks exposed to 10 mM NaHCO₃. As a result of 10 mM NaHCO₃, the expression of a Cu/Zn-SOD and a POD isoform was diminished in the leaves of ‘Peach seedling’ and ‘Barrier,’ respectively. By contrast, an additional isoform of both POD and Mn–SOD were expressed in the leaves of ‘GF-677’ exposed to 10 mM NaHCO₃ suggesting that the tolerance of rootstocks to Fe deficiency is associated with induction of an antioxidant defense mechanism. Although CAT activity was increased in the 5 mM NaHCO₃-treated leaves of ‘GF-677,’ specifically the 10 mM NaHCO₃ treatment resulted in a decrease of CAT activity and an accumulation of H₂O₂, indicating that bicarbonate-induced Fe deficiency may cause more severe oxidative stress in the rootstocks, than the absence of Fe. A general link between Fe deficiency-induced oxidative stress and Fe reduction-sensing mechanism is also discussed.     

C-NMR detection of lipid polymorphism in model and biological membranes

1. 1. The application of the ¹³C-NMR technique to the study of lipid polymorphism is described for various model and biological membranes.

2. 2. The ¹³C-NMR line-width of various resonances of the lipid molecule are sensitive to the bilayer hexagonal and the bilayer ‘isotropic’ phase transition. The latter transition in some cases is accompanied by the occurrence of lipidic particles as detected by freeze-fracturing. Thus, specific ¹³C-labeling experiments allow the study of the individual phase behaviour of lipids in mixed lipid systems.

3. 3. In diet experiments using rats, the choline group of phosphatidylcholine present in erythrocyte, endoplasmic and sarcoplasmic reticulum membranes could be specifically ¹³C-labeled. The ¹³C line-widths of the resonance from the erythrocyte are typical for a lamellar arrangement of the membrane lipids. In strong contrast, the line-width observed at 37°C for the endoplasmic and sarcoplasmic reticulum membranes is much smaller, typical of the isotropic phases observed in model membranes. In isolated rat liver microsomes and liver slices, the ¹³C line-width is strongly temperature dependent. At lower temperatures the line-widths strongly increase towards values typical of lipids in a bilayer structure.

Enhancement in ‘apparent’ membrane microviscosity during differentiation of embryonal carcinoma cells induced by retinoids

Upon differentiation of embryonal carcinoma cells induced by retinoids (10⁻⁷ M) the ‘apparent’ membrane microviscosity increases dramatically. Only biologically active retinoids induce differentiation and cause an enhancement in microviscosity. Several embryonal carcinoma cell lines have a relatively lower ‘apparent’ microviscosity than their differentiated derivatives, suggesting that this may be a general property of these cells. At higher concentrations retinoids cause a reduction in ‘apparent’ membrane microviscosity of various cells. This change occurs whether the analogue is biologically active or not, indicating the non-specific nature of this action.     

The influence of amphotericin B on the permeability of mammalian erythrocytes to nonelectrolytes, anions and cations

The influence of the polyene antibiotic, amphotericin B, on the permeability of porcine and bovine erythrocytes was studied by measuring net and tracer movements of nonelectrolytes, anions and cations in these cells.

1. 1. Amphotericin B (0.5–20 μM) enhances the rates of transfer of hydrophilic nonelectrolytes (glycerol, erythritol), anions (phosphate, lactate, glycollate, Cl⁻, SCN⁻) and cation (Na⁺, K⁺). Different concentrations of the antibiotic are required for equal effects on the different transfer processes. Bovine erythrocytes respond much less to amphotericin than porcine cells.

2. 2. Nystatin enhances the transfer of all the permeants to a much lesser extent; gramicidin D, although producing a large increase of cation permeability, leaves unaltered anion and nonelectrolyte transfer.

3. 3. The amphotericin-induced enhancement of erythrocyte permeabability (ΔP) increases with time. It has a concentration dependence of the type ΔP = α · Cⁿ_A^* (n = 1.5–2.5) and becomes more pronounced at low temperatures.

4. 4. Partial depletion of membrane cholesterol, which in itself does not alter nonelectrolyte and anion permeability, reduces the effectivity of amphotericin B, indicating that in the erythrocyte membrane, too, a sterol acts as receptor for polyene antibiotics.

5. 5. The selectivity of the amphotericin-induced pathway of transfer in the erythrocyte membrane is lower than that of the normal pathways of nonelectrolyte and anion transfer in this membrane.

The results support the view that amphotericin produces the same type of molecular reorganisation of lipid constituents in biological and artificial membranes. On the other hand, the polyene-induced pathway in the erythrocyte membrane seems to differ functionally from the normal transfer pathways in this membrane.     

Cytogenetic stability of <Emphasis Type="Italic">Centaurea ragusina</Emphasis> long-term culture

Centaurea ragusina L. (Asteraceae) is an endemic Croatian plant species, which developed xeromorphic characteristics as a consequence of its natural environment – vertical limestone cliffs above the Adriatic sea. Cytogenetic status of C. ragusina long-term culture (94th subculture) and C. ragusina seedlings was analysed and compared after 4 weeks of growth. Cytogenetic stability was investigated in root meristem cells of C. ragusina cultured plants originated from Pen đa (cliffs near Dubrovnik) and seedlings originated from three different localities in south Adriatic (Penđa, Pasjača – cliffs near Dubrovnik and island of Komiža) using mitotic index and mitotic and chromosomal abnormalities as parameters. Mitotic indices of cultured plants and ‘Penđa’ seedlings were similar and showed significant increase compared to mitotic indices of ‘Komiža’ and ‘Pasjača’ seedlings. Although the highest number of mitotic abnormalities was recorded in root meristem cells of cultured plants, it was only a bit higher than in root tips of ‘Pasjača’ and ‘Penđa’ seedlings, while that of ‘Komiža’ was two times lower compared to cultured plants. Pattern of analysed mitotic abnormalities was very similar in root tips of cultured plants and ‘Pasjača’ and ‘Penđa’ seedlings, with exception of ‘Komiža’ seedlings. Presented results suggest that long-term cultivation of C. ragusina has almost no effect on culture ageing considering similar distribution of scored mitotic abnormalities as in ‘Penđa’ and ‘Pasjača’ seedlings.     

Molecular Systematics of Middle American Cichlid Fishes and the Evolution of Trophic-Types in ‘Cichlasoma(Amphilophus)’ and ‘C.(Thorichthys)’

The majority of Middle American cichlids are placed in the informal assemblage ‘Cichlasoma.’ The group is divided into eight sections which appear to be based primarily on trophic morphology. Although several members of ‘Cichlasoma’ have been used in ecomorphological, behavioral, and biogeographic studies, no phylogenetic hypotheses for the group exist. In an attempt to develop a better understanding of the phylogenetic relationships of ‘cichlasomine’ cichlids, we examined the evolution of the trophic specialization, substratum-sifting, in two sections, ‘Cichlasoma(Thorichthys)’ and ‘C.(Amphilophus),’ to determine whether the trait reflects common ancestry. We sequenced the complete mitochondrial cytochromebgene for 19 cichlids representing six sections of ‘Cichlasoma,’ and representatives of other Neotropical Cichlidae. Additional cichlid, and noncichlid outgroup sequences were included for a total of 22 taxa. The molecular phylogeny supports the recognition of the section ‘C.(Thoricthys)’ as a natural group, and we place those cichlids in the genusThorichthys.The phylogeny also depicts ‘C.(Amphilophus)’ as paraphyletic, with substratum-sifters and generalized predators forming separate nonsister clades. We recommend that the substratum-sifting clade of the section ‘C.(Amphilophus)’ be placed in the resurrected genusAstatheros.The generalized predator clade of ‘C.(Amphilophus)’ contains only two species, ‘C. (A.) citrinellum’ and ‘C. (A.) labiatum,’ which we place in the genusAmphilophus.The phylogenetic hypotheses generated indicate that the substratum-sifting generaThorichthysandAmphilophusdo not share a common ancestor. Reconstruction of the evolution of substratum-sifting is equivocal, requiring either the independent evolution of the trait on two separate occasions or its presence in a more inclusive clade and subsequent loss in nonsubstratum sifting species.     

Distinguishing kinds of prior dominance and subordination experiences in males of green swordtail fish (Xiphophorus helleri)

In experiments, there are usually two general ways of obtaining dominants and subordinates to test for the effect of recent experience upon ulterior behavior and dominance. One is to ‘impose’ such an experience on the contestants by a priori deciding which individual of the pair will become the dominant and which will become the subordinate through the use of rigged contests. The second technique is to let contestants ‘self-select’ the winner and loser by waiting for the spontaneous outcome of dyadic encounters between two usually well matched opponents. These two techniques of obtaining dominants and subordinates probably represent extreme cases on a single continuum of investment made by animals to settle dominance. To test this, we compared dominants and subordinates obtained from these two techniques in Xiphophorus fish males. It was found that pairs obtained through rigged contest (R) were much more aggressive in subsequent encounters than pairs in which the dominant and subordinate could self-select (S). They recuperated more rapidly from handling, initiated contact earlier, took more time to assess each other, and fought for a longer period of time. Prior-winners and prior-losers of the R condition more frequently relied on aggressive behavior during contest than that of the S condition. As a consequence, prior-winners and prior-losers of the R condition won equally the subsequent contest. On the contrary, prior-winners of the S condition defeated their prior-loser opponent in a majority of cases. These results can be tentatively explained by the following principle, winning or losing against a well matched opponent would leave more ‘experience’ than winning over a much weaker opponent, or losing to a much stronger one. This reinforces the hypothesis that prior-experiences are not qualitative states but come in various degrees.     

The distribution of zinc, cadmium, lead and copper within the hepatopancreas of a woodlouse

The distribution of metals within the hepatopancreas of Oniscus asellus (Crustacea, Isopoda) from two uncontaminated sites, and two sites contaminated with zinc, cadmium and lead, has been studied by atomic absorption spectrophotometry, light microscopy, transmission and scanning electron microscopy and X-ray microanalysis. The hepatopancreas contains two types of intracellular granule. The first type, in the S cells, are spherical granules which contain copper, sulphur and calcium. In woodlice from contaminated sites, these ‘copper’ granules, also contain zinc, cadmium and lead. The second type, in the B cells, are flocculent deposits which contain iron. In woodlice from contaminated sites, these ‘iron’ granules also contain zinc and lead. Moribund woodlice from contaminated sites have large numbers of ‘copper’ and ‘iron’ granules in the hepatopancreas and a fine deposit of zinc and lead on the membranes of the cells. There are numerous microorganisms in close association with the microvillous border of the hepatopancreas of woodlice from all four sites. Within the microorganisms of Oniscus asellus from contaminated sites, there are deposits of material which contain zinc, lead, calcium and phosphorus ‘Copper’ and ‘iron’ granules could have evolved as storage sites for essential metals to be utilized when demand from the body exceeds uptake from the food. Woodlice in contaminated sites may be able to ‘detoxify’ potentially harmful amounts of essential and non-essential metals by storing them in a relatively insoluble form within these granules.     

DNA replication in macronuclei of Tetrahymena pyriformis GL

DNA replication in macronuclei of Tetrahymena pyriformis GL has been studied to discriminate between hypotheses developed for the interpretation of intraclonal differentiation in ciliated protozoa (the diploid subnuclear, and the ‘master’-‘slave’ hypotheses). Tetrahymena cells were grown in a heavy ¹⁵N-³H medium and then transferred to a light ¹⁴N-¹⁴C medium. DNA was isolated after various periods following this transfer and studied in equilibrium CsCl density gradient centrifugation. Time-related changes in the DNA buoyant density pattern were investigated. The data obtained are interpreted to mean that all DNA in macronuclei of asynchronously growing Tetrahymena at exponential phase replicates semiconservatively once in a cell cycle. These data are in good agreement with the findings of Andersen & Zeuthen obtained on synchronous Tetrahymena cultures in the presence of BUdR.These results are not consistent with the ‘master’-‘slave’ hypothesis. The diploid subnuclear hypothesis is not in accord with other experimental evidence. An alternative hypothesis has been proposed concerning the nature of the macronuclear units and the process of determination. The two main points of this hypothesis are: (a) macronuclear units are diploid genome fragments (‘nucleosomes’); (b) determination is a process of haploidization by ‘allelic splitting’ at a definite macronuclear fission. Consistency with experimental data is discussed and some predictions of the hypothesis are given.