Gene assignment by means of somatic cell hybrids: a new method for the analysis of data

Summary A statistical approach to the interpretation of data from gene assignment with somatic cell hybrids is presented. The observed data are analysed under a variety of hypotheses. The fit to the hypotheses is compared by means of the likelihood obtained under a given hypothesis. Two of these hypotheses are related to fundamental questions: is a gene responsible for the enzyme observation and if so, is that gene located on a specific chromosome or could it change its position and be sometimes on chromosome j and, in another hybrid line, on chromosome k? The other hypotheses concern the assignment of the gene to just one of the chromosomes.To improve the traditional data analysis approach we considered additional information: the uncertainties and possible errors of laboratory methods in all our calculations and the length of the donor chromosomes in connection with one specific hypothesis.This method allows us to account for the reliability of the investigation methods and the nature of the hybrid lines involved. Data can be evaluated at different error probabilities within a realistic range in order to compare and discuss results.     

Community metabolism on rocky-shore assemblages in a mesocosm: A. Fluctuations in production,respiration, chlorophyll a content and C:N ratios of grazed and non-grazed assemblages

Studies were undertaken with the aim of developing a standardized method for assessing environmental pollution in sediments by utilization of life-history data of freshwater tubificids. Similar bioassay methods have long been used for Daphnia magna, species of Ceriodaphnia and Nitocra, etc. in accordance with guidelines from the International Organization for Standardization (ISO). Tubifex tubifex was found to be the most likely candidate for such bioassays, since the species is readily kept in culture and reproduces more or less consistantly.The culturing method is slightly modified from Kosiorek (1974). This paper provides an example of the particular sensitivity of this kind of bioassay method in the detection of heavy metal contamination of lake sediments. Sediments from the oligotrophic Lake Runn were considered suitable for the purpose, since the lake receives waste water from a major mining industry in Sweden. Metal analyses of the sediments had revealed the agents likely to be causing the decreased biological activity measured in the lake; rough amplitudes for mercury: 800–3600 ng · g^-1 dw, copper: 800–1800 g · g^-1 dw, zinc: 3.3 – 8.1 mg · g g^-1 dw have been estimated for surficial sediments.Young tubificids exposed to Lake Runn sediments did not grow much and died off within a short period of time. No reproduction occurred. Sediments from Lake Runn, when mixed with sediments from the eutrophic Lake Hjälmaren, made reproduction of T. tubifex occur only in mixtures containing less than 50% L. Runn sediments. The growth rate, reproductive success and the very timing of consecutive reproductive events of cohort individuals were found to be highly indicative of toxic effects. When additional food sources were available, however, these effects were largely masked. Therefore, extra food rations were excluded from the original method.     

Effect of rainstorms on heterotrophic bacterial activity in a hypertrophic African lake

Hartbeespoort Dam is a hypertrophic man-made lake which is located in the Transvaal Province of South Africa. This region has recently experienced its most severe drought of the century. However, on three occasions in the summer rainy seasons of 1984 and 1985, major rainfalls (> 50 mm) occurred which caused large inflows to the lake. Inflowing river water entered as a density current causing marked silting of the water. Within the epilimnion (0–10 m) prior to these rainfalls there was usually no variation of bacterial numbers with depth, but heterotrophic bacterial activity (glucose uptake) decreased with depth concomitant with primary production. With the increased river inflow bacterial numbers did not increase but bacterial activity at the bottom of the epilimnion (10 m) increased to as high as 2.7 µg C l^–1 h^–1 in January 1985, reversing the depth profile of bacterial activity within the epilimnion. This resulted in decreased glucose concentrations (K_t + S_n) and turnover times. Heterotrophic activity per cell increased by between 2.5 and 5 times. These data demonstrate that storm events are important phenomena causing short-term changes in the metabolic activity of planktonic heterotrophic bacteria in lakes.     

D2O and the sodium pump in squid nerve membrane

Summary In 10 K artificial seawater (ASW). D₂O replacement reduced the Na efflux of squid axons by about one third. In 0 K ASW, D₂O replacement had little effect. D₂O reduced the K⁺ sensitivity of the efllux but increased the affinity for K⁺. A 4° decrease in temperature mimicked the effects of D₂O. When axons were injected with arginine, to decrease the ATP/ADP ratio, they lost K⁺ sensitivity in normal ASW, as expected. Their efflux into 0 K ASW became D₂O sensitive. The results are discussed in terms of conformational changes in the Na pump molecular complex.     

Modulation of water and urea transport in human red cells: Effects of pH and phloretin

Summary It has previously been shown by Macey and Farmer (Biochim. Biophys. Acta 211:104–106, 1970) that phloretin inhibits urea transport across the human red cell membrane yet has no effect on water transport. Jennings and Solomon (J. Gen. Physiol. 67:381–397, 1976) have shown that there are separate lipid and protein binding sites for phloretin on the red cell membrane. We have now found that urea transport is inhibited by phloretin binding to the lipids with aK ₁ of 25±8 m in reason-able agreement with theK _D of 54±5 m for lipid binding. These experiments show that lipid/protein interactions can alter the conformational state of the urea transport protein. Phloretin binding to the protein site also modulates red cell urea transport, but the modulation is opposed by the specific stilbene anion transport inhibitor, DIDS (4,4-diisothiocyano-2,2-stilbene disulfonate), suggesting a linkage between the urea transport protein and band 3. Neither the lipid nor the protein phloretin binding site has any significant effect on water transport. Water transport is, however, inhibited by up to 30% in a pH-dependent manner by DIDS binding, which suggests that the DIDS/band 3 complex can modulate water transport.     

An investigation into thee mechanism of citrate---FE-dependent lipid peroxidation

Chelation by citrate was found to promote the autoxidation of Fe²⁺, measured as the disapperance of 1,10-phenanthroline-chelatable Fe²⁺. The autoxidation of citrate---²⁺ could in turn promote the peroxidation of microsomal phospholipid liposomes, as judged by malondialdehyde formation. At low citrate---Fe²⁺ ratios the autoxidation of Fe²⁺ was slow and the formation of malondialdehyde was preceded by a lag phase. The lag phase evidence of this, linear initial rates of lipid peroxidation were obtained via the combination of citrate---Fe²⁺ and citrate---Fe³⁺, optimum activity occurring at a Fe³⁺---Fe²⁺ ratio of 1:1. Evidence is also presented to suggest that the superoxide and the hydrogen peroxide that are formed during the autoxidation of citrate---Fe²⁺ can either stimulate or inhibit lipid peroxidation by affecting the yield of citrate---Fe³⁺ from citrate---Fe²⁺. No evidence was obtained for the participation of the hydroxyl radical in the initiation of lipid peroxidation by citrate---Fe²⁺.     

Facultative parthenogenesis and sex-ratio evolution

Summary Phenotypic models of selection are used to determine the effect of facultative parthenogenesis on the production of males in a spatially variable environment when (i) sex determination is under strict genetic control, and (ii) when sex may be environmentally determined. The results show that when sex is under strict genetic control and there is some chance of maturing in isolation, selection favors a female-biased sex ratio. When sex can be environmentally induced by cues which indicate high density, selection favors a mixture of genetic and environmental control, such that half the individuals always become female and the other half become females when isolated and become males when not isolated.     

Changes in gill histology of fathead minnows and yellow perch transferred to soft water or acidified soft water with particular reference to chloride cells

Summary Fathead minnows, Pimephales promelas, and yellow perch, Perca flavescens, were transferred from moderately soft Lake Superior water (hardness 45mg/l as CaCO₃) to very soft diluted Lake Superior water (hardness 4.5mg/l). Sulfuric acid was added in some treatments by means of a multichannel diluter. In very soft water, chloride cells proliferated in the gills, especially in the epithelium of the secondary lamellae. When exposed to acid, chloride cells were damaged and less abundant in the secondary lamellae, and blood osmolality was reduced at pH 5.0 (x = 188 mOsm/kg, 9 days exposure; normal 280 mOsm/kg) for the minnows and pH 4.1 (x = 218 mOsm/kg, 58 days exposure; normal 329 mOsm/kg) for the perch. Certain chloride cells which form gland-like clusters in the primary lamellae of perch gills showed little damage even at pH 4.1. The present study supports the view that chloride cells proliferate in very soft fresh water to help maintain ionic balances, and that damage to these cells in acidified soft water may be related to diminished ionoregulatory capacity. The greater acid tolerance of chloride cells of, and the higher blood osmolality maintained by, perch could help to explain the greater tolerance of this species to low pH. In some cases, a species' ability to acclimate to very soft water and acidified soft water may depend upon the number, distribution, and physiology of its chloride cells.     

The dispersal unit of Dacrycarpus dacrydioides (A. Rich.) de Laubenfels (Podocarpaceae) and the significance of the fleshy receptacle

FOUNTAIN, D. W., HOLDSWORTH, J. M. & OUTRED, H. A., 1989. The dispersal unit of Dacrycarpus dacrydioides (A. Rich.) de Laubenfels (Podocarpaceae) and the significance of the fleshy receptacle. Dacrycarpus dacrydioides (formerly Podocarpus dacrydioides ) is an arborescent gymnosperm endemic to New Zealand. The high water content (43%) and sensitivity of viability towards desiccation, suggest the seeds are of the 'recalcitrant' type. The 'fruits' comprising a seed borne on a fleshy receptacle arc shed in large numbers. The development of the seed precedes the full development of succulence in the receptacle and at maturity the seed has a high relative water content (RWC) relative to the receptacle. Within the maturing reproductive unit, the receptacle buffers the seed against the effects of water stress. After shedding, seeds are rapidly desiccated in moving air, and viability is impaired below approximately 80"' RWC and abolished at 34", seed RWC. The presence of the receptacle during drying confers resistance to desiccation-associated damage. Five phases of desiccation sensitivity are distinguished in recognition of the protective role of the receptacle. It is suggested that the advantages associated with prolonging seed viability may have contributed to the evolutionary development of succulence in the reproductive unit. This might be considered as a selection pressure in a manner similar to the proposal that such fleshy structures are associated with seed dispersal by birds.