Effects of sulfate on cadmium uptake by Swiss chard: II. Effects due to sulfate addition to soil

Sulfate complexation of Cd in nutrient solution has been shown to have little impact on Cd uptake by plants. This study examined the effect of sulfate added to soil on Cd concentrations in soil solution and Cd uptake by Swiss chard (Beta vulgaris L. cv. Fordhook Giant). Swiss chard was grown in soil which was wetted with complete nutrient solution containing equivalent salt concentrations of NaNO₃ or Na2SO₄. Plant growth was reduced by increasing both NO₃ and SO₄ concentrations in soil solution, with growth reductions similar for both salts. The Cd concentration in soil solution increased P< 0.05) more consistently with increasing concentrations of SO₄ compared to NO₃ in soil solution. Solution speciation, calculated with GEOCHEM-PC, showed significant increases of Cd2+ activities with increasing salt rates. Shoot Cd content in 19-day-old Swiss chard plants was marginally but significantly P <0.05) increased with increasing SO₄ concentration but no effect was observed with increasing NO₃ concentration. These results are compared with earlier work on the marked effect of Cl- salinity on Cd availability in Swiss chard. Possible mechanisms explaining the smaller effect of SO₄ compared to Cl on Cd availability are proposed.     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂SeO₃ to nutrient enriched artificial seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10⁻² M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga find all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

STEADY-STATE LUXURY CONSUMPTION AND THE CONCEPT OF OPTIMUM NUTRIENT RATIOS: A STUDY WITH PHOSPHATE AND NITRATE LIMITED SELENASTRUM MINUTUM (CHLOROPHYTA)1

Selenastrum minutum (Naeg.) Collins was grown over a wide range of growth rates under phosphate or nitrate limitation with non-limiting nutrients added to great excess. This resulted in saturated luxury consumption. The relationships between growth rate and cell quota for the limiting nutrients were well described by the Droop relationship. The observed variability in N cell quota under N limitation as reflected in k_Q·Q_max^?1*, was similar in magnitude to previously reported values but k_Q·Q_max^?1* for P under P limitation was greater than previously reported for other species. These results were evaluated in light of the optimum ratio hypothesis. Our findings support previous work suggesting that the use of a single optimum ratio (k_Qi·K_Qj^?1) is inappropriate for dealing with a species growing under steady-state nutrient limitation. Under these conditions the optimum ratio should be viewed as a growth rate dependent variable. Two approaches for testing the growth rate dependency of optimum ratios are proposed. The capacity for luxury consumption differed between nutrients and was growth rate dependent. At low growth rates, the coefficient of luxury consumption (R_sat) for P was ca. four times that for N. The set of all possible relationships between N and P cell quota under these conditions was reported and these values were then used to establish the cellular N:P niche boundaries for S. minutum. Cell quotas of non-limiting nutrients were not described by the Droop equation. Analysis showed that as the cellular N:P ratio deviates from the optimum ratio, the ability of the Droop equation to describe the relationship between growth rate and non-limiting cell quotas decreases. When non-limiting nutrient cell quotas are saturated, the Droop equation appears to be invalid. Previously reported patterns of non-limiting nutrient utilization are summarized in support of this conclusion. The physiological and ecological consequences of luxury consumption and growth rate dependent optimum ratios are considered.     

The Influence of pH on the Cadmium-Repressed Growth of the Alga Coelastrum proboscideum

The inhibition of growth by different concentrations of CdCl₂ in the range 4,5 × 10^?7 to 5.6 × 10^?7M was studied in the green alga Coelastrum proboscideum Bohlin in inorganic media at pH 4.3, 5.3 and 6.2. The factorial destgn of the experiments was evaluated as an analysis of 2² factors. Below pH 4.0 and above pH 6.5 growth was depressed without adding Cd. Cd concentrations exceeding 5.6 × 10^?8M reduced algal growth significantly with a 50% inhibition at 5.6 × 10^?7M Cd. The Cd concentration of 5.6 × 10^?7M was less toxic at pH 6.2 than at pH 5.3 and 4.3, thus revealing a negative interaction between protons and Cd.     

RESPONSES OF FRESHWATER ALGAE TO INHIBITORY VANADIUM CONCENTRATIONS: THE ROLE OF PHOSPHORUS1

We found that species-specific differences exist among a variety of freshwater algae and cyanobacteria in the extent to which growth and photosynthesis are inhibited by vanadium. A major factor controlling the degree of inhibition by vanadium was the phosphorus state (P-sufficient vs. P-deficient) of the organisms. In P-sufficient cultures, vanadium was inhibitory when the vanadium concentration exceeded the phosphate concentration. In P-deficient cultures, the depression of photosynthesis by vanadium increased with increasing phosphorus deficiency. Our conclusion that vanadium competed with phosphate for uptake sites was supported by the following three observations: 1) the decreased influx of ³²P-PO ₄ into P-deficient cells in the presence of vanadium, 2) the amelioration of vanadium inhibition of photosynthesis by the addition of phosphate, and 3) the accumulation of vanadium by cells. At vanadium concentrations that severely inhibited growth, the cells of Scenedesmus obliquus (Turp.) Kruger were larger than normal and contained more vacuoles, lipid, and starch bodies than normal cells. Four-celled coenobia were replaced by unicells. Scenedesmus acutusf: alternans Hortobagyi cells from vanadium-inhibited cultures had 7.5 times more vanadium per cell than control cultures and contained numerous granules that did not stain for polyphosphate and may be composed of condensed vanadate molecules. The cellular P quota and turnover time of PO₄in the medium are important regulators of the extent of inhibition by vanadium.     

NUTRITIONAL STUDIES OF THE EDIBLE SEAWEED PORPHYRA TENERA. II. NUTRITION OF CONCHOCELIS1

The nutrition of the free-living phase of Conchocelis of P. tenera was studied axenically. Conch-ocelis preferred NO₃, as nitrogen source. Urea and NH₄ in low concentration, asparagine, and lysine were very good N sources. Several other amino acids were also utilized but growth was less abundant. Inorganic and organic phosphates were utilized; they were required at relatively low concentrations. Glycerophosphate gave excellent growth in a comparatively wide range of concentrations (0.1-5 mg P %). The optimal Ca concentration was 10-100 mg %. Needs for boron, manganese, zinc, strontium, rubidium, lithium, and iodine were demonstrated. The iodine effect was remarkable (peak growth with 1μg %); the effective concentration range was very narrow. Iron, cobalt, and bromine seemed to be adequately supplied as impurities of the macro-nutrients. A modified artificial medium (ASP₁₂I) for the Conchocelis phase is presented.     

ALGORITHM FOR APPLICATION OF FOURIER ANALYSIS FOR BIORHYTHMIC BASELINES OF PHARMACODYNAMIC INDIRECT RESPONSE MODELS

The change of an indirect pharmacological response R(t) can be described by a periodic time-dependent production rate k_in (t) and a first-order loss constant k_out. If k_in(t) follows some biological rhythm (e.g., circadian), then the response R(t) also displays a periodic behavior. A new approach for describing the input function in indirect response models with biorhythmic baselines of physiologic substances is introduced. The present approach uses the baseline (placebo) response R_b(t) to recover the equation for k_in(t). Fourier analysis provides an approximate equation for R_b(t) that consists of terms (usually two or three) of the Fourier series (harmonics) that contribute most to the overall sum. The model differential equation is solved backward for k_in(t), yielding the equation involving R_b(t). A computer program was developed to perform the square L²-norm approximation technique. Fourier analysis was also performed based on nonlinear regression. Cortisol suppression after inhalation of fluticasone propionate (FP) was modeled based on the inhibition of the secretion rate k_in(t) using ADAPT II. The pharmacodynamic parameters k_out and IC₅₀ were estimated from the model equation with k_in(t) derived by the new approach. The proposed method of describing the input function needs no assumption about the behavior of k_in(t), is as efficient as methods used previously, and is more flexible in describing the baseline data than the nonlinear regression method. (Chronobiology International, 17(1), 77–93, 2000)     

SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂eO₃ to nutrient enriched artifical seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10_-2 M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga and all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

NUTRITIONAL REQUIREMENTS OF HAEMATOCOCCUS PLUVZALIS AND RELATED SPECIES1

All the described species and varieties of the genus Haematococcus were available. After isolation in pure culture they were used studying their nutritional requirements. H. buetschlii and H. droebakensis had already been shown by Droop to need vitamin B₁₂. H. capensis typ., H. capensis var. borealis, and H. zimbabwiensis were found to do so also. The 7 strains of H. pluvi-alis from various localities investigated showed slight physiological deviations, although morphologically they were so similar that they should not be described as varieties. A dilute inorganic nutrient solution with trace elements and iron kept in solution by EDTA was suitable either as such or supplemented with growth-promoting compounds. The growth was speeded by low concentrations of acetate and by enhancing photosynthesis. No strain of H. pluvialis absolutely required cobalamin, although it stimulated. Thiamine had a much more pronounced effect; for some strains it was indispensable. Although the response varies slightly from strain to strain, a luxuriant growth for all was obtained only with acetate and B₁, and usually enhanced by B₁₂. A peculiar feature of H. pluvialis is the catching up of cultures initially retarded by thiamine deficiency (probably due to slow B_l synthesis). When H. pluvialis multiplied fast its appearance differed from that considered typical: no red pigment and the cell wall not inflated. In nature it evidently lives under conditions unfavorable for good growth although suitable for survival in competition with other organisms.     

Cadmium and copper interactions on the accumulation and distribution of Cd and Cu in birch (Betula pendula Roth) seedlings

The effect of different external cadmium (Cd) and copper (Cu) regimes on the concentration of Cd and Cu in roots and shoots of birch (Betula pendula Roth.) seedlings was investigated. The seedlings were grown for 12 days in a weak nutrient solution (containing all essential nutrient elements including 0.025 µM Cu) at pH 4.2 with combinations of additional 0–2 µM CdCl₂ and 0–2 µM CuCl₂. Root and shoot concentrations of Cu were decreased by Cd in all treatments which included 0.1–2 µM of additional Cu in the treatment solution. When no extra Cu was added, only the shoot concentration of Cu was decreased by Cd whereas the root concentration was not affected. The shoot concentration of Cd was decreased by 0.5 and 2 µM of additional Cu in the treatment solution. The root concentration of Cd was decreased by Cu only when the concentration of additional Cu in the treatment solution was equal to or exceeded the concentration of Cd.     

An algebraic model for the kinetics of covalent enzyme inhibition at low substrate concentrations

This article describes an integrated rate equation for the time course of covalent enzyme inhibition under the conditions where the substrate concentration is significantly lower than the corresponding Michaelis constant, for example, in the Omnia assays of epidermal growth factor receptor (EGFR) kinase. The newly described method is applicable to experimental conditions where the enzyme concentration is significantly lower than the dissociation constant of the initially formed reversible enzyme–inhibitor complex (no “tight binding”). A detailed comparison with the traditionally used rate equation for covalent inhibition is presented. The two methods produce approximately identical values of the first-order inactivation rate constant (k_inact). However, the inhibition constant (K_i), and therefore also the second-order inactivation rate constant k_inact/K_i, is underestimated by the traditional method by up to an order of magnitude.     

Kinetic behavior of heterogeneous populations in completely mixed reactors

The kinetic behavior of heterogeneous microbial populations was studied in a continuous flow completely mixed reactor operated at various dilution rates. Glucose was used as the growth-limiting nutrient. The physiological growth parameters for cells harvested from continuous flow reactors were determined using batch experiments. It, was found that the growth parameters, maximum growth rate (μ_m), saturation constant (k_s), and cell yield (Y) vary for each dilution rate, and cannot be considered as precise constants in depicting the kinetic behavior of heterogeneous populations. In addition, it was found that the yield coefficients obtained from batch experiments were always lower than those obtained from continuous flow experiments. Levels of substrate and biological solids calculated for different dilution rates using growth constants from batch experiments did not agree with the experimental values observed in steady-state experiments. However, when the yield values from, the continuous flow experiments were used in conjunction with batch values for μ_m and k_s the theoretical and experimental dilute-out curves agreed fairly closely (within the range needed for engineering prediction) until the culture began to wash out of the unit. In general, the data substantiated the use of the single phase relationship between growth rate and substrate concentration described by the Monod equation, μ = μ_mS/(k_s + s).     

Effects of pH and heavy metal concentrations in solution culture on the proton release,growth and elemental composition ofAlyssum murale andRaphanus sativus L.

The proton release by a species that can hyperaccumulate nickel (Alyssum murale) and by a non-accumulator (Raphanus sativus L.) was studied at different pH and heavy metal concentrations in solution culture. Both factors influenced the growth and composition of the plants.A. murale was more sensitive than radish to a decrease of pH from 7.0 to 6.0 in the growth medium; plant yield and proton production diminished with decreasing pH. However, yields and proton production of radish only decreased at pH 5.5. The differences in the amounts of protons produced between the hyperaccumulator species and radish were not large enough to conclude that decreasing pH in the rhizosphere ofA. murale is a mechanism for heavy metal solubilization.Nickel concentrations inA. murale followed the typical pattern of an accumulator plant — more Ni was accumulated in the shoots than in the roots. Lower concentrations of Zn and Cd occurred in the shoots than in roots ofA. murale, and also of Ni in radish. The concentrations of Co inA. murale shoots were increased when Zn, Ni and Cd were absent from the nutrient solution. However, Co concentrations in radish shoots were independent of the concentrations of other heavy metals in the growth medium.     

COMPARISON OF HALF-SATURATION CONSTANTS FOR GROWTH AND NITRATE UPTAKE OF MARINE PHYTOPLANKTON 2

Growth rates and rates of nitrate uptake by N-depleted cells were measured for an oceanic diatom, Chaetoceros gracilis, and a neritic diatom, Asterionella japonica, as functions of nitrate concentration of the medium. Both growth and N-uptake rates appeared to be hyperbolic with nitrate concentration and could be fit to an equation of Michaelis-Menten form: where v is rate, V^m. is the maximum rate, S is nitrate concentration, and K_sis the half-saturation constant. K_svalues for uptake and growth were similar if not identical for each species. Uptake experiments can provide a presumptive measure of K_sfor growth, thought to be an ecologically significant characteristic of a species.     

Short-and long-term effects of cadmium on transmembrane electric potential (E m) in maize roots

In this study, the effects of Cd on root growth, respiration, and transmembrane electric potential (E _m) of the outer cortical cells in maize roots treated with various Cd concentrations (from 1 μM to 1 mM) for several hours to one week were studied. The E _m values of root cells ranged between −120 and −140 mV and after addition of Cd they were depolarized immediately. The depolarization was concentration-dependent reaching the value of diffusion potential (E _D) when the Cd concentration exceeded 100 μM. The values of E _D ranged between −65 to −68 mV (−66 ± 1.42 mV). The maximum depolarization of E _m was registered approx. 2.5 h after addition of Cd to the perfusion solution and in some cases, partial (Cd > 100 μM) or complete repolarization (Cd < 100 μM) was observed within 8–10 h of Cd treatment. In the time-dependent experiments (0 to 168 h) shortly after the maximum repolarization of E _m a continuous concentration-dependent decrease of E _m followed at all Cd concentrations. Depolarization of E _m was accompanied by both increased electrolyte leakage and inhibition of respiration, especially in the range of 50 μM to 1 mM Cd, with the exception of root cells treated with 1 and 10 μM Cd for 24 and 48 h. Time course analysis of Cd impact on root respiration revealed that at higher Cd concentrations (> 50 μM) the respiration gradually declined (∼ 6 h) and then remained at this lowest level for up to 24 h. All the Cd concentrations used in this experiment induced significant inhibition of root elongation and concentrations higher than 100 μM stopped the root growth within the first day of Cd treatment. Our results suggest that Cd does not cause irreversible changes in the electrogenic plasma membrane H⁺ ATPase because fusicoccin, an H⁺ ATPase activator diminished the depolarizing effect of Cd on the E _m. The depolarization of E _m in the outer cortical cells of maize roots was the result of a cumulative effect of Cd on ATP supply, plasmalemma permeability, and activity of H⁺ ATPase.     

A mathematical description of short-term effects of β-lactam antibiotics on bacterial growth in vitro

Bacterial growth at moderately high concentrations of β-lactam antibiotics and within the first few hours of exposure cannot be described by a simple exponential equation. The quadratic function InN _t=InN ₀+k₀t?1/2at², in whichk ₀ is the initial growth rate constant anda a rate inhibition constant, is a better approximation. Whena is used as a single parameter, the effect of a particular antibiotic can be described as a concentration-effect relation. This approach also permits comparison of antibiotics, e.g., nafcillin and cloxacillin. The relation betweenk ₀ anda in the interaction between nafcillin and chloramphenicol shows that chloramphenicol antagonizes the effect of nafcillin.     

NUTRITIONAL REQUIREMENTS OF HAEMATOCOCCUS PLUVIALIS AND RELATED SPECIES1

All the described species and varieties of the genus Haematococcus were available. After isolation in pure culture they were used studying their nutritional requirements. H. buetschlii and H. droebakensis had already been shown by Droop to need vitamin B₁₂. H. capensis typ., H. capensis var. borealis, and H. zimbabwiensis were found to do so also. The 7 strains of H. pluvialis from various localities investigated showed slight physiological deviations, although morphologically they were so similar that they should not be described as varieties. A dilute inorganic nutrient solution with trace elements and iron kept in solution by EDTA was suitable cither as such or supplemented with growth-promoting compounds. The growth was speeded by low concentrations of acetate and by enhancing photosynthesis. No strain of H. pluvialis absolutely required cobalamin, although it stimulated. Thiamine had a much more pronounced effect; for some strains it was indispensable. Although the response varies slightly from strain to strain, a luxuriant growth for all was obtained only with acetate and B₁, and usually enhanced by B₁₂. A peculiar feature of H. pluvialis is the catching up of cultures initially retarded by thiamine deficiency (probably due to slow B₁ synthesis). When H. pluvialis multiplied fast its appearance differed from that considered typical: no red pigment and the cell wall not inflated. In nature it evidently lives under conditions unfavorable for good growth although suitable for survival in competition with other organisms.     

Optimal design for CSTR's in series using reversible Michaelis-Menten reactions

An analytical expression is derived for the optimal design of a series of CSTR's performing reversible Michaelis-Menten kinetics in the liquid phase. The optimal design is based on minimum overall volume ofN reactors in series required to achieve a certain degree of substrate conversion. The reversible Michaelis-Menten equation is also able to explain competitive product inhibition and irreversible Michaelis-Menten kinetics. The reversible Michaelis-Menten kinetics covers three types of enzymatic reactions depending on the values of the rate constant for the forward (k _s) and reverse (k _p) reactions. An optimum design is obtained in the three cases ofK _s=K_p, K_s>K_p andK _s<K_p. The minimum overall reactors volume is compared with the more convenient equal-sized CSTR's. The effect of enzyme deactivation on the minimum overall reactors volume is investigated. The performance of a series of CSTR's is compared with plug-flow reactor. Glucose isomerization which exhibits reversible Michaelis-Menten kinetics is used as a model system for optimization.     

Toxicity of cadmium to twoStreptomyces species as affected by clay minerals

Summary The effect of cadmium on the growth ofStreptomyces rimosus andS. bottropensis (both isolated from soil) was investigated. The modifying effect of the presence of the clay minerals kaolinite, bentonite and vermiculte on Cd toxicity was also included. After four days no growth was observed at 100 ppm CdCl₂ ofS. bottropensis and at 150 ppm in case ofS. rimosus. After six days some growth ofS. rimosus occurred at 150 ppm CdCl₂ and ofS. bottropensis at 100 ppm. Addition of the three clay minerals decreased the Cd toxicity considerably.     

Effect of berberine on growth of the callus cultures of several species

A bacteriostatic concentration of berberine much inhibited growth of the callus cultures ofLithospermum erythrorhizon, Datura inooxia andCarthamus tinctorius, but little inhibited the callus growth ofMacleaya cordata. On the other hand, the high concentration of berberine tended to stimulate the callus growth ofCoptis japonica var.japonica. Among callus cultures of the five species described above, 4-desoxypyridoxine inhibited growth of the callus cultures ofD. innoxia andC. tinctorius. In these two callus cultures, recovery effects of some of the vitamin B₆ group (10 μg/ml) on the inhibition of callus growth by berberine (100 μg/ml) or 4-desoxypyridoxine (50 μg/ml) were observed.