Some features of feeding,respiration and energy conversion of Dapnia Magna

Some results of studies with Daphnia magna are presented. These results can be used as background information for toxicologists, but the techniques referred to might well be used for toxicity tests. Daphnia magna is a filter-feeder. With the Coulter Counter it was shown that the feeding mechanism is aselective for size of the food particles. It was also shown that algal cells can pass the gut of Daphnia magna several times before being completely digested. The uptake of food is proportional to the food concentration up to a critical concentration. Above this concentration the food uptake is constant. Respiration is also dependent on the food concentration, and has a maximum value at food concentrations near the critical concentration of the feeding process. Growth efficiency is independent of the food concentration. The effect of temperature on the feeding process is different for low and high food concentrations. Growth efficiency is maximal at 10°C and above 22°C growth efficiency was negative, which means that the population cannot survive under the experimental conditions used, at temperatures above 22°C.     

Studies on populations of Folsomia candida (Insecta: Collembola)

Summary Experiments are described that were designed to investigate the effects of food availability and rate of exploitation on the growth and production of populations of Folsomia candida (Willem). In an initial experiment in which there was excess food it was found that increasing the rate of exploitation resulted in increases in both the numerical and biomass productivity of the populations. In a second experiment it was shown that, when there is severe competition for food, the rate of exploitation does not affect either the biomass or the numerical production. It is concluded that the effect of overcrowding, in the form of competition for space, does contribute to the growth in numbers of populations, but that the supply of food plays a more important role in regulating the population. Anomalous results, showing that exploitation has a lesser effect when there is severe competition for food, are discussed.     

The sampling characteristics of electivity indices

Summary Electivity indices measure the utilization of food types (r) in relation to their abundance or availability in the environment (p). Foods that constitute a larger proportion of the diet than of the available foods are considered preferred; conversely those proportionately underrepresented in the diet are avoided. A food is eaten at random if its proportion in the diet equals its proportion in the environment. A family of electivity indices stemming from Ivlev's (1961) classic monograph exist and differ only in the particular algorithm used to calculate electivity from r and p.For each available index I graphed the values of electivity as contours for all combinations of r and p. These graphs are compared to illustrate the strengths and weaknesses of each index on the basis of the following criteria: 1) the value of the index when r=p for a food, 2) the symmetry of the electivity value as feeding deviates from random, 3) the possible range of index values, 4) the linearity of changes in electivity over the full range of r and p, 5) the sensitivity of the index to sampling errors, 6) the statistical testability of the electivity, and 7) the stability of the electivity value for a food type that changes relative abundance or occurs in combination with different food types. No one index ideally satisfies all the criteria.The host preferences of gypsy moth, Lymantria dispar, feeding on tree foliage in an undisturbed deciduous forest in southwestern Quebec, Canada were used to compare the available indices: Ivlev's electivity, E; Ivlev's forage ratio, E'; Jacob's modified electivity, D; Jacob's modified forage ratio, log Q; Chesson's alpha; Strauss' linear index, L; and Vanderploeg and Scavia's relativized electivity, E ^*. The electivity values calculated by each index differ one from another; host trees shown as preferred by one index will frequently appear avoided according to an alternative index. The rank order electivities for the 19 available host trees, however, are remarkably similar for all but Strauss' linear index, L. Populus grandidentata, Quercus rubra, Ostrya virginiana, and Amelanchier were the most preferred host trees in the sampled forest; Prunus serotina, Acer pensylvanicum, A. rubrum, Betula lutea, and Fraxinus americana were most avoided. The use of Vanderploeg and Scavia's E ^* index is recommended.     

The effect of the nutrient intensity and buffering power of a soil,and the absorbing power,size and root hairs of a root,on nutrient absorption by diffusion

Summary A portion of a single plant root is treated as an absorbing cylindrical sink to which nutrients move by diffusion. Assuming that the rate of uptake of nutrient is proportional to its concentration at the root surface, and that the nutrient, though reacting with the solid, moves only through the soil solution, standard diffusion equations are used to calculate the effect of soil and plant characteristics on the rate of uptake. The treatment is applicable to phosphorus and potassium. Among soil properties uptake should increase directly with the soil solution concentration. It should also increase, but only slowly, with increasing buffering power. It increases with increasing soil moisture. Among plant characteristics, uptake should increase with the root absorbing power until diffusion through the soil becomes limiting. Absorption by unit surface area of root increases as the root radius decreases. A root hair is shown to interfere quickly with the uptake of adjacent hairs. The hairs increase absorption by the root because they can exploit rapidly the soil between the hairs, and they have the effect of extending the effective root surface to their tips.     

Energy-limitation of a sodium-independent amino acid transport in ovarian oocytes of the frog

The frog, Rana pipiens, hibernates through the winter with ovaries containing oocytes which, in size and appearance, are ready for ovulation and maturation. From November through April, the normal time of egg laying, ovulation and maturation can be induced by interrupting hibernation and administering gonadotropic hormones. In the studies reported here, it has been found that oocytes taken from hibernating animals in early winter take up amino acids from a saline medium at a relatively rapid rate. Respiratory inhibition produced by such agents as dinitrophenol (DNP) and anaerobiosis, does not completely stop uptake but slows it down markedly. In late winter, amino acid uptake tends to be slower in normal cells and when DNP or cyanide is added, a marked acceleration of the rate of uptake is observed. The uptake in poisoned cells is accumulative, producing internal concentrations higher than that of the medium. At this concentration of DNP, amino acid incorporation is almost completely stopped. Fluoride abolishes the DNP stimulation of amino acid uptake. Removal of sodium ion from the incubating medium has no effect on either uptake or incorporation. These data are interpreted to mean that a capacity for oxidative phosphorylation in oocytes diminishes during winter hibernation. In the spring either an anaerobic capacity comes into being or becomes capable of being switched on. During this time the rate of amino acid uptake, even in the downhill phase, is limited by energy availability and is not dependent on a sodium gradient.     

Effect of killer toxin K1 on yeast membrane potential reported by the diS-C3(3) probe reflects strain-and physiological state-dependent variations

The rate and extent of uptake of the fluorescent probe diS-C₃(3) reporting on membrane potential inS. cerevisiae is affected by the strain under study, cell-growth phase, starvation and by the concentration of glucose both in the growth medium and in the monitored cell suspension under non-growth conditions. Killer toxin K1 brings about changes in membrane potential. In all types of cells tested,viz. in glucose-supplied stationary or exponential cells of the killer-sensitive strain S6/1 or a conventional strain RXII, or in glucose-free exponential cells of both strains, both active and heat-inactivated toxin slow down the potential-dependent uptake of diS-C₃(3) into the cells. This may reflect “clogging” of pores in the cell wall that hinders, but does not prevent, probe passage to the plasma membrane and its equilibration. The clogging effect of heat-inactivated toxin is stronger than that exerted by active toxin. In susceptible cells,i.e. in exponential-phase glucose-supplied cells of the sensitive strain S6/1, this phase of probe uptake retardation is followed by an irreversible red shift in probe fluorescence maximumλ _max indicating damage to membrane integrity and cell permeabilization. A similar fast red shift inλ _max signifying lethal cell damage was found in heat-killed or nystatin-treated cells.     

THE COMPARATIVE CELL CYCLE AND METABOLIC EFFECTS OF CHEMICAL TREATMENTS ON ROOT TIP MERISTEMS. I. IOXYNIL

In this study we investigated the cell cycle response of Vicia faba and Pisum sativum root tip meristems to ioxynil treatments at two concentrations, (10^−-4m and 10^−-6m ). After 24 h of treatment at 10^−-4m concentration, O₂ uptake and ATP concentrations were significantly reduced. The mitotic index was reduced and the cell cycle population position was shifted to indicate that previously inhibited cells reformed their nuclei and became tetraploid. Prolonged treatment at this concentration resulted in cell death. Treatment with ioxynil at 10^−-6m reduced the rate of entry into mitosis. Abnormal mitotic figures in all stages were observed, and the ploidy level of mitotically inhibited cells was doubled. These observations indicated that at 10^−-6m concentration ioxynil acts as a preprophase inhibitor, that is, it does not act directly on the mitotic apparatus but does affect processes on which mitosis depends.     

Uptake and metabolism of myo-inositol by L1210 leukaemia cells.

The initial rate of uptake of [3H]myo-inositol by L1210 murine leukaemia cells is directly proportional to the extracellular concentration and unaffected by several analogues of myo-inositol even at millimolar concentrations. Scyllitol, a geometric isomer of myo-inositol, partially inhibited the uptake of myo-inositol (40% at 0.1 mM). A portion of the uptake of myo-inositol was not inhibited even at 5 mM-scyllitol. At steady-state the intracellular concentration of [3H]myo-inositol is directly proportional to the extracellular concentration. Addition of myo-inositol to medium does not enhance the growth of L1210 cells; these cells can maintain an extracellular concentration of 20 microM-myo-inositol even when grown in myo-inositol-free medium. Synthesis of myo-inositol from glucose by L1210 cells was demonstrated by use of [13C]glucose and m.s. L1210 cells maintain myo-inositol pools by a combination of synthesis de novo and uptake of exogenous myo-inositol by either passive diffusion or a low affinity carrier.     

Uptake of Nitrate by Mutants of Arabidopsis thaliana, Disturbed in Uptake or Reduction of Nitrate

The uptake of nitrate by wildtype plants and chlorate-resistant mutants of Arabidopsis thaliana (L.) Heynh. was studied by intermittent or continuous measurement of the nitrate concentration of the ambient solution. The uptake rate in the wildtype and the nitrate reductase-less mutant B 25 showed a dual-phase relation ship with concentration. Each phase showed Michaelis-Menten kinetics although multiphasic patterns within each phase could not be excluded. A dual-phase relationship was also found in the uptake mutant B I. Here, however, phase II did not follow Michaelis-Menten kinetics and uptake rate of nitrate in the phase II concentration range was considerably lower in the B 1 mutant than in the wildtype. It is concluded that the mutation in B I has disturbed phase II of the nitrate uptake, without affecting phase I, which leads to the suggestion that uptake of nitrate in Arabidopsis is mediated by at least two independent uptake mechanisms. The nitrate uptake rate showed an optimum at pH 8, and it was not stimulated by the presence of calcium. Ammonium had different effects on nitrate uptake: a direct effect, when it was present during the uptake of nitrate, resulting in a release of nitrate and a reduced rate of uptake, and an indirect inhibitory effect, possibly caused by assimilation products of ammonium, which is most pronounced after growth on ammonium as the sole nitrogen source or in long-lasting uptake experiments in the presence of ammonium. Chlorate also showed a multiple effect, an inhibiting one which proved to be competitive and, at very low concentrations of chlorate, a stimulating one. Evidence was obtained that chlorate and nitrate arc taken up by the same carrier.     

Regulation of uridine uptake by serum and insulin in density-inhibited 3T3 cells

Stimulation of nucleoside uptake in quiescent 3T3 cells by insulin and serum is preceded by a substantial lag phase. Our findings point to the length of the lag phase as a major target for regulation. The length of such phase varies markedly with the concentration of insulin (10^?9-10^?6 M) or serum (0.5–10%) but it is not eliminated by high, saturating levels of the activating agents. Further, variations in the temperature at which the stimulation process occurs 24–39°C), addition of compounds like prostaglandin E₁ (1–5 μg/ml) or theophylline (0.4 mM) and differences in the age of the cultures primarily affect the length of the lag time while the final uptake rates achieved are remarkably constant. Analysis of the temporal order of the events in the lag phase reveals that there is a discrete temperature-sensitive period located in the early and middle part of the lag, while the prostaglandin E₁-sensitive step(s) appear to be toward the end of the lag. The transition from the basal to the stimulated rate of uptake is abrupt. Indeed, the kinetics of activation does not fit a simple exponential law but a high power of an exponential, suggesting that the switching mechanism involves cooperative steps. Since the transition is abrupt, the nucleoside uptake system exists largely in two alternative states either switched off or on. The regulation of the lag period is by the control of the time at which this switch occurs. On the basis of the data presented here, we propose a working hypothesis of uptake stimulation.     

DNA Synthesis Cycle in Blepharisma*

SYNOPSIS. Observations made with tritiated thymidine uptake indicate that Blepharisma cannot utilize this precursor directly from the organic medium. An intermediary, such as a food organism (bacteria or Tetrahymena, is needed. These food organisms are not only capable of incorporating thymidine from the medium, but must also break it down or prepare it in a form that is utilizable for Blepharisma. DNA synthesis phase in Blepharisma occurs 17 hours after division. Maximum incorporation is obtained 18 and 19 hours postdivision and lasts thru 24 hours. This is followed by a 1–2 hour postsynthesis phase and division.     

Relationship between substrate concentration,growth rate,and respiration rate of Escherichia coli in continuous culture

Summary Using a continuous flow technique the relationship between growth rate and substrate concentration was investigated with glucose as the limiting factor of a culture of Escherichia coli. Graphical and numerical analysis of the experimental data demonstrated that the application of the Michaelis-Menten equation produced erroneous results, whereas, the constants obtained from the Teissier equation were in agreement with the experimental data. On this basis, new equations defining the steady state cell and substrate concentration in continuous flow cultures were developed and tested against experimental data.Comparison of the specific growth rates, substrate uptake rates and oxygen consumption rates demonstrated that all were directly proportional to each other and could be related to each other by mathematical equations. Specifically it was shown that as the growth rate increased from 0.06 to k _m =0.76 the substrate uptake rate increased from 134 to 1420 mg glucose per gram cell weight per hour and the oxygen consumption rate increased from 48.6 to 505 mg O₂ per gram cell weight per hour. Independent of the growth rate 37% of the carbohydrate consumed were oxidized. The yield factor varied from 0.44 at low growth rates to 0.54 at high growth rates. Analysis of the growth rate-substrate uptake rate relationship indicated that a minimum substrate uptake rate of 55 mg glucose per gram cell weight per hour existed below which cell reproduction would cease. This was supported by the fact that steady state conditions could not be maintained in the culture at D values below 0.02 when the substrate supply rate decreased below 45 mg glucose per gram cell weight per hour.Material contained in this paper was submitted as a thesis in partial fulfillment of the requirements for the Ph. D. degree of Dr. R. S. Lipe.     

Cell surface changes during the differentiation of Dictyostelium discoideum : Interaction of cells with Concanavalin A

The parameters affecting the agglutination of cells of Dictyostelium discoideum by Concanavalin A (ConA) have been investigated. Under the incubation conditions employed, incubation time does not markedly affect agglutination, but there are distinct optima for cell density and gyration speed. Agglutination does not occur at low temperatures, but the transition temperature between the unagglutinated and fully agglutinated states is markedly influenced by ConA concentration. The rate of aggregation of strain NC-4 is considerably reduced by ConA. In contrast, the differentiation of strain Ax-2 in the presence of ConA is either unaffected or only slightly inhibited, depending on the incubation conditions. Succinylated-ConA binds to the same sites as the unmodified lectin, but has no effect on the differentiation of strain NC-4, suggesting that ConA binding sites are not directly involved in cell-cell contacts vital to the differentiation of D. discoideum. There is a gradual decrease in the susceptibility of cells of D. discoideum to agglutination by ConA as the cells pass from exponential growth phase to stationary growth phase in axenic medium and from vegetative amoebae to aggregates on a solid substratum. These results provide quantitative evidence for a gradual change in carbohydrate containing binding sites during differentiation.     

Food limitation of asexual reproduction in a spionid polychaete

Summary

The rate of asexual fragmentation in the spionid polychaete Pygospio elegans is shown to increase in the presence of augmented food levels and is a density-dependent response. Asexual reproduction does not occur when the animals are reproducing sexually.     

Recent developments for making gastric evacuation and daily ration determinations

Synopsis Gastric evacuation rate estimates often suffer from an important bias caused by fitting experimentally-derived data distributions that are inherently constricted by the X-axis (Y = 0). Monte Carlo simulations were used to evaluate the bias. Truncating constricted distributions prior to curve fitting was suggested as a means to circumvent the problem. A food consumption model developed by D.S. Robson was presented. It employs the integral of the function fit to percentage gastric evacuation data, and does not require an a priori assumption of exponential gastric evacuation. The methods were illustrated using experimental gastric evacuation data and stomach contents data for fishery-caught yellowfin tuna, Thunnus albacares.     

A simple experimental approach to the Determination of carrier transport parameters for unlabeled substrate analogs

A method is described by which affinities and transport rates for unlabeled substrate analogs are readily determined, and which is based on the effect of an unlabeled analog upon the rate of transport of a labeled substrate present at a low concentration on the trans side of the membrane. The procedure is widely applicable since it does not depend on assumptions about rate-limiting steps and holds for both active and non-active systems. Here it is applied in an experimental study of the facilitated diffusion system for choline in erythrocytes, and it is shown that the transport parameters for a test substrate obtained by this method are the same as those found when the transport of the substrate is followed directly.     

Inhibitory and Toxic Effects of Blue-green Algae on Daphnia

The effects of the planktonic blue-green algae, Aphanizomenon gracile, Synechococcus elongatus, and Microcystis aeruginosa, on survival, growth, and food uptake of Daphnia pulicaria were determined. Synechococcus and Aphanizomenon were unsuitable food when offered alone, but did not affect the daphnids negatively when mixed with Scenedesmus. Microcystis was the only one found to be toxic. In pure suspensions of this blue-green, the daphnids did not survive more than 48 hours; they lived a little longer if Scenedesmus was supplied additionally. Growth was markedly reduced when only 50 μg carbon/l of Microcystis was added to the normal Scenedesmus food. It ceased at a concentration of 250 μg C/l. This can be explained by the reduction of food uptake. Very small quantities of Microcystis (10 μg C/l) present in the normal food caused a significant reduction of the filtering rate. Filtering inhibition was associated with the cells. Filtrate of Microcystis suspensions was not effective. Thus, the daphnids must ingest the blue-green cells in order to become toxified. Dual-labelling experiments showed that Microcystis cells are filtered from the medium by Daphnia with the same efficiency as Scendesmus and are not rejected. Toxicity of Microcystis is considered to be an effective defence mechanism against grazing pressure.     

Rapid-growth responses of corn root segments: Effect of citrate-phosphate buffer on elongation

Summary Chloroplasts from the alga, Vaucheria dichotoma (L.) Ag., are taken up into protoplasts of carrot (Daucus carota L.) during polyethylene-glycol treatment. Since chloroplasts are found with equal frequency in uni- and multinucleate protoplasts, chloroplast uptake does not depend on protoplast fusion. However, higher frequencies of chloroplast uptake are observed when experimental conditions favor greater aggregation of protoplasts. The intracellular localization of chloroplasts is confirmed by electron microscopy, and it is shown that the chloroplasts, once within the protoplasts, are not surrounded by a limiting membrane of carrot origin.     

Potassium and phosphate uptake of cucumber plants at different ammonia supply

Summary Experiments on cucumber plants grown in nutrient solution were conducted in order to study long and short time effects of ammonia on growth, nutrient element uptake and respiration of roots.Shoot yield and potassium concentration in tissue of plants treated 18 days with varied ammonia concentration were decreased. However, it was not assumed that K deficiency caused the yield reduction. The ammonia effect on K content was more pronounced in roots than in shoots.The decreased K concentration of plant tissue was linked to a diminished ability of plant roots to absorb potassium. The maximum rate of potassium uptake was lowered by ammonia during both, long- and short-time treatment. The results indicated that the NH₃ influence on potassium uptake was due to effects on metabolism and permeability of roots because changes of K uptake rate occurred immediately after starting the NH₃ treatment. Furthermore, it is shown that ammonia inhibited respiration of roots.During the short-time treatment net potassium efflux of roots was observed at higher NH₃ concentrations. The extent of K efflux depended on K concentration of both, root tissue and nutrient solution.Pretreating the plants for 12 hours with ammonia also resulted a decline in K uptake rate. However, plant roots subjected to ammonia concentrations up to 0.09 mM completely recovered during 24 hours after removing the NH₃ treatment whereas at higher NH₃ concentrations only a partial recovery occurred.Furthermore, it was shown that ammonia also influenced P uptake by plant roots.