Effect of intermittent CO2 enrichment during nutrient starvation on tertiary treatment of wastewater by alginate-immobilized Scenedesmus bicellularis

A method of accelerating the removal of ammonium and phosphate by the unicellular microalga Scenedesmus bicellularis is presented for municipal tertiary wastewater treatment using immobilized cells to obtain a high quality of effluents. Microalgal cells grown in defined medium were harvested by centrifugation and stored at 4°C in the dark for 8 months before immobilization. The concentrated cell suspension was then immobilized in alginate films supported on polypropylene screens. Immobilized cells were incubated in a water-saturated air stream enriched with CO₂ at 750, 1,000, or 1,500 ppm for 3 h periods followed by 2 h periods without enrichment. The quantitative effects of these three CO₂ enrichments on nutrient uptake from secondary municipal wastewater effluent were compared to a control laboratory air at 320 ppm under the same conditions of illumination, photoperiod, and humidity. The exposure cycle of 48-h nutrient deprivation in air with CO₂ enrichment followed by 2 h of nutrient uptake from wastewater was repeated three times with a residual NH₄---N content dropping to 0% after 105 min for the 1,500 ppm CO₂ treatment and to 34% of the initial level after 120 min for the control treatment. Complete PO₄---P removal required more than 2 h. The chlorophyll a contents obtained with 1,000 and 1,500 ppm CO₂ enrichments were comparable. This study establishes that intermittent CO₂ enrichment during nutrient deprivation of immobilized microalgal cells in a water-saturated air stream may accelerate tertiary wastewater treatment.     

Plasma glucose kinetics and tissue uptake in brown trout in vivo: effect of an intravascular glucose load

The object of the present study was to elucidate whether a glucose load modifies glucose uptake by tissues in brown trout in vivo. By the use of 2-[1,2-³H]-deoxyglucose, plasma glucose disappearance rate and tissue glucose uptake were measured after an intraaortic glucose load of 500 mg·kg^-1 (glucose load group) and under normoglycemic conditions (control). We also attempted to determine whether fasting modifies the glucose load disposal (fasted glucose load group). The procedure used to calculate 2-deoxyglucose uptake by tissues was evaluated, and the levels of 2-deoxyglucose uptake were compared with those of 2-deoxyglucose phosphorylation. Uptake and phosphorylation rates were similar in all tissues, except in brain and heart. In all the groups glucose uptake rates were highest in spleen, kidney, brain and gills, and lowest in red muscle, heart and white muscle. However, white muscle was the main site of glucose uptake on a whole tissue basis. The glucose load led to strong, long-lasting hyperglycemia, in spite of the increases observed in plasma insulin levels and in glucose uptake rate by the whole body (control: 4.9 mol·min^-1·kg^-1; glucose load group: 6.5 mol·min^-1·kg^-1). This higher rate was due to the higher glucose uptake only in white and red muscles (four- and threefold, respectively). Fasting halved the uptake of glucose by both red and white muscles in the load condition. In consequence the use of exogenous glucose decreased with fasting (fasted glucose load group: 5.1 mol·min^-1·kg^-1), causing still longer hyperglycemia.Abbreviations bw body weight - 2DG 2-[1,2-³H]-deoxyglucose - 2DG-P 2-[1,2-³H]-deoxyglucose phosphate - dpm disintegrations per min - FGL fasted glucose load group - GL glucose load group - G-6-Pase glucose-6-phosphatase - LG L-[1-¹⁴C]-glucose - MS-222 3-aminobenzoic acid ethyl ester methanesulphonate salt     

Soil water dynamics in an oak stand

A model describing water uptake by plants with particular attention to the soil-root interface under transient conditions is derived and discussed. Field data on a daily scale enable the unknown parameters of the model to be determined with the help of an identification technique. The model is then used to analyse the experimental results presented in part I of this paper. The loss of total conductivity of the soil-tree system under drought conditions whereas the metabolism of the trees seems to remain unaffected can be explained by the increase of the soil-root resistance. In fact this resistance becomes the limiting factor when the volumetric soil water content decreases (below =0.33 for the superficial layer and 0.36 for the deeper one in the studied case). Such values can be frequently encountered at the end of summer.     

DNA uptake by imbibition and expression of a foreign gene in rice

Uptake of DNA by imbibition of dry and viable rice ( Oryza sativa L.) embryos from a DNA solution and expression of a foreign gene were detected using two different vectors contaíning gusA (β-glucuronidase) and hpt (hygromycin phosphotransferase) as reporter genes. The frequency of transient expression of gusA and hpt genes using the CaMV35S promoter was about 30 to 50%. The main sites of gusA gene expression were meristems of roots and vascular bundles of leaves. Also, DNA uptake, integration and expression of the hpt gene in selected rice were investigated by various PCR methods and Southern blot analysis of genomic DNA. It was shown that the hygromycin phosphotransferase (HPT) DNA was present in the rice genome in an integrated form and not as a plasmid form.     

Micronutrient composition of xylem sap and needles as a result of P-fertilization in maritime pine

Xylem sap and foliar compositions (P, Cu, Zn, Mn) were examined over 4 months in control and P-fertilized maritime pine in a 7-year-old plantation. The absorption of copper, zinc, and boron appears to be reduced by phosphate fertilization. Manganese concentrations are positively related to P-supply increase. Foliar analysis and sap provides the same type of information in terms of antagonism or synergism between elements but the response to treatment is more often significant with sap throughout the seasons and is completely non-existent on a single classical autumn diagnosis with foliar concentration (i.e. Zn and Cu). In consequence foliar analysis is not sensitive enough for copper or zinc deficiency diagnoses in young plantations where nutritional growth disorders appear in a short period of spring, and xylem chemistry appears to be a convenient tool in monitoring micronutrient disorders in pine plantations.     

Effect of cations,including heavy metals,on cadmium uptake by Lemna polyrhiza L.

Cations, including calcium, magnesium, potassium, sodium, copper, iron, nickel and zinc, inhibited (up to 40%) extracellular binding and intracellular uptake of cadmium by Lemna polyrhiza in solution culture. Test plants showed a high capacity of extracellular cadmium binding which was competitively inhibited by copper, nickel and zinc; however, calcium, magnesium and potassium caused non-competitive inhibition. Iron and sodium increased K _m and decreased V _max, thereby causing mixed inhibition of extracellular binding. Intracellular cadmium uptake displayed Michaelis-Menten kinetics. It was competitively inhibited by calcium, magnesium, iron, nickel and zinc. Monovalent cations (sodium and potassium) caused non-competitive and copper caused mixed inhibition of intracellular cadmium uptake. Thus, high levels of cations and metals in the external environment should be expected to lower the cadmium accumulation efficiency of L. polyrhiza.     

Characterization of the blue light-induced extracellular alkalinization associated with the monovalent anion uptake by Monorapidium braunii. Competition between NO3 and Cl−

The blue light-elicited monovalent anion-dependent alkalinization of the medium of Monoraphidium braunü (Legnerová, 202–7d) was characterized for the NO-³ and Cl- uptake. The maximal H⁺ uptake rates for these two anions have a similar optimum pH around 8.5, and quite similar K^s values for high (38 üM for Cl- and 35üM for NO-³) and low (320 üM for Cl- and 335 üM for NO-³) affinities. The steady H⁺ uptake associated with the uptake and reduction of NO-³ showed a K^s of 125 üM. which in this alga corresponds to the NO-³ reductase (EC 1.6.6.2) K^m for NO-³. The only and striking difference found in the uptake properties of these anions was the delay time between the switching on of the blue light and the start of the alkalinization, which increased from 10 to 90 s as the initial pH decreased from 8.5 to 6.5 in the presence of NO-³, whereas for Cl- uptake this delay time (10s) did not vary in relation to the initial pH. When the NO-³ concentration in the medium was low (100 üM), the presence of relatively high concentrations of Cl- (3 üM), on the one hand, greatly stimulated the maximal alkalinization rates but, on the other, Cl- severely reduced the steady NO-³-dependent rate of alkalinization. The data indicate that Cl- inhibits competitively NO-³ uptake with a Kⁱ of 750 üM. Moreover, high concentrations of NO-³ (above 5 üM) reduced its own maximal, but not the steady, uptake rates. The above results allow us to propose that most of the components of the individual NO-³ and Cl- transport systems are under identical light control and, as the competition data suggest, that these two anions may be taken up by the same transport system.     

Regulation of K+ and NO3− fluxes in roots of sunflower (Helianthus annuus) after changes in light intensity

Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K⁺ and NO₃⁻ uptake by roots, both uptake of K⁺ and NO₃⁻ and secretion into the xylem of young sunflower plants ( Helianthus annuus L.) were measured after changes in light intensity.
No close correlation was observed between the uptake of NO₃⁻ and that of K⁺; an increase in light intensity produced a much greater stimulation of NO₃⁻ uptake than of K⁺ uptake. On the other hand, secretion of NO₃⁻ into the xylem was tightly coupled to that of K⁺, and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K₂-malate shuttle on the regulation by the shoot of K⁺ and NO₃⁻ secretion in the xylem, which is linked to NO₃⁻ uptake, while K⁺ uptake is independent of this regulation mechanism.     

Zinc deficiency does not enhance LDL uptake by P 388 D1 macrophages in vitro

The aim of the study was to investigate the effect of zinc depletion on the susceptibility of Wistar rat low-density lipoproteins (LDL) to peroxidation and their uptake by macrophages, before and after in vitro oxidation. The rats were fed for 7 wk a Zn-adequate diet (100 ppm) ad libitum (AL), a Zn-deficient diet (0.2 ppm) ad libitum (ZD), or a Zn-adequate diet according to the pair-feeding method (PF). Zinc status was determined and, for each group, blood was pooled, and LDL were isolated and labeled with¹²⁵Iodine. An aliquot of each LDL sample was oxidized using Fe^II 10 μM/ascorbate 250 μM. Oxidized and nonoxidized (native) LDL were incubated with P 388 D1 macrophages, and their rates of uptake and degradation by macrophages were measured. Before oxidation, LDL uptake and degradation were not modified by the diet, suggesting that Zn deficiency did not modify rat LDL in vivo. After oxidation, both LDL uptake and degradation were significantly enhanced in the three groups. Nevertheless, we did not observe a significant effect of Zn deficiency. This observation suggests that, in our experimental conditions, Zn deficiency did not modify LDL catabolism.     

Is low rooting density of faba beans a cause of high residual nitrate content of soil at harvest ?

It was the aim of this study was to evaluate the hypothesis that low rooting density of faba beans is the major reason for the comparable low depletion of N_min-nitrogen from the rooted soil volume during the vegetation period. Therefore a simulation study was carried out using data from a two-year field experiment with faba beans and the reference crop oats. Since the nitrate dynamics in the soil is closely coupled with the water budget, the model simulated also the water uptake by plants, movement and content in the soil applying a numerical solution of the Richard's equation. The nitrogen budget part of the model includes calculation of vertical nitrate movement in the soil, mineralisation of nitrate from organic matter and nitrate uptake by the crop. Vertical nitrate movement was simulated with the convection-dispersion equation. Mineralisation was computed from a simple first order kinetic approach using only one fraction of mineralisable organic matter. Nitrate uptake was assumed to be determined either by the nitrogen demand of the crop, which was estimated from a logistic growth equation that was fitted to measured data of N-accumulation, or by the maximum nitrate transport rate towards the root surface. The latter was computed from a steady state solution of the diffusion - mass flow equation for cylindrical co-ordinates.For oats the model calculated a maximum nitrate transport rate towards roots that was quite close to the measured N-uptake of that crop. For faba beans, however, the calculated maximum nitrate transport towards roots was much lower than total N-uptake and lower than for oats. Consequently, simulated N_min-contents below faba beans were during the growing season about 20-30 kg N ha^–1 higher than below oats. This difference matches quite close with the observed differences between the two crops. Therefore it was concluded that low nitrate uptake resulting from low rooting density is the main reason for higher residual nitrate contents below faba beans at harvest time.