Optical assessment of phytoplankton nutrient depletion

The ratio of light absorption at 480 and 665 nm by 90% acetoneextracts of marine phytoplankton pigments has been examinedas a potential indicator of phytoplankton nutritional statusin both laboratory and field studies. The laboratory studiesdemonstrated a clear relationship between nutritional status(carbon/nitrogen ratio) and the absorption ratio that was independentof light and temperature climate. The absorption ratio for nutrient-repletecells was shown to vary between taxonomic groups. However, theinter-specific variation was less than the differences observedbetween nutrient-replete and nutrient-depleted cells. The fielddata suggest that the absorption ratio may be a useful indicatorof nutritional status of natural phytoplankton populations,and can be used to augment the interpretation of other data.     

Glucose uptake by chicken embryo hearts at various stages of development

d-glucose, but not l-glucose, was found to readily enter the cells of 5- to 6-day chick embryo heart. This suggests the operation of a specific transport system for glucose. The rate of glucose uptake was found to decrease as development proceeds from 5 to 15 days of development, but no further decrease was found between 15 and 20 days. Uptake of glucose is a saturable process, from 5–6 days of embryonic life on. The large decrease in glucose uptake between 5 and 10 days of development is found to be associated with a fourfold increase in the apparent K_m of the uptake process. From 10 days of development onward, the apparent K_m remains about 40 mM. The rate of 2-deoxyglucose uptake also decreased from 5 to 15 days of embryonic life with no further decrease from 15 to 20 days. Glucose competitively inhibits the uptake of 2-deoxyglucose with a K_i close to the K_m for glucose uptake. The uptake of 2-deoxyglucose is stimulated by physiological levels of insulin as early as 5–6 days, although the extent to which insulin enhances uptake is not quite as great as at 15 days of development.     

Rates of oxygen uptake by embryonic anterior horn tissue isolated at various developmental stages.

Neuroepithelial cells of the presumptive spinal cord (stage 11) consume oxygen, albeit at a low rate. As neurons differentiate in the presumptive motor horns the rate of oxygen consumption increases to approximately 70 mumoles/g wet wt/hr by stage 26. It is suggested that the rate of oxygen consumption per unit volume of neuron then remains constant as subsequent development ensues but since the neurons become more widely spaced the oxygen consumption per unit volume of anterior horn tissue decreases.     

Nitrogenous nutrient uptake by phytoplankton and ammonium regeneration by microbial assemblage in Lake Biwa

In situ rates of nitrate, ammoniwn and urea uptake by the phytoplanktonassemblage, and the regeneration rate of ammonium by the microbialassemblage, in Lake Biwa were measured using the nitrogen 15tracer method from 1985 to 1987. The rate of total nitrogen(sum of ammonium, nitrate and urea) uptake was in the rangeof 62–594 ng N^–1 r^–1 h^–1. The percentagecontribution of ammonium uptake was 41–92%, that of urea4–58% and that of nitrate <1–28% of total uptake.The annual mean new production which was supported by nitrateuptake was 18% of the total production in 1986. The phytoplanktonassemblage in Lake Biwa preferentially utilized regeneratednitrogen, such as ammonium and urea, whose concentration wasmuch lower than that of nitrate throughout the observation penodwithout in summer. The in situ nitrogen uptake rate was almostsufficient to meet the nitrogen requirement of the phytoplanktonassemblage, except in midsummer when the nitrate concentrationwas below the detection limit of 0.3 µg N r^–1. Inthe trophogemc layer, the rate of ammonium regeneration was66–272 ng N 1^–1 h^–1 Although the ambient ammoniumconcentration in the trophogenic layer was maintained at aroundthe half-saturation constant for ammonium uptake kinetics, theammomum uptake rates were always highly correlated with ammoniumregeneration rates. From the size fractionation experimentsand estimates from the literature, it was suggested that themicrobial assemblage <1 µm may have been the most importantagent responsible for the ammonium regeneration processes inthe trophogenic layer.     

Total uptake of nutrients at different stages of the growth of groundnut and the ratios in which various nutrient elements exist in groundnut plant

Summary A pot experiment was conducted with groundnut crop in two red soils with various levels of application of calcium, phosphorus, potassium and magnesium. The plants were analysed at vegetative, reproductive and post harvest stages for the uptake of nutrients. Up to vegetative stage, the crop absorbed 10 per cent of the total requirement of nitrogen, phosphorus, calcium and magnesium. During the reproductive stage the crop removed about 40 to 50 per cent of the above nutrients. Between reproductive and harvest stages groundnut absorbed the remaining amount of the nutrients.Forms a part of the Ph.D. thesis of the first author approved by Tamil Nadu Agricultural University.     

Growth and nutrient uptake of coniferous seedlings: Comparison among 10 species at various seedbed densities

Summary The evaluation of biomass production and uptake of N, P, K, Ca, and Mg for various plant components (roots, stems, and foliage) and totals by 10 species of 2-0 coniferous seedlings grown at a controlled range of densities in a highly productive forest nursery documents considerable differences among species and seedling parameters. The species are ranked by biomass and nutrient-element relationships on a unit area of seedbed basis, quantifying the magnitude of the differences among the species at the various density levels. The 10 species include Abies balsamea, Larix leptolepis, Picea abies, Picea glauca, Picea mariana, Picea pungens, Pinus resinosa, Pinus strobus, Pinus sylvestris, and Pseudotsuga menziesii.Contribution of the Forest Resources Council, School of Environmental and Resource Management, State University of New York College of Environmental Science and Forestry, Syracuse, New York 13210.Contribution of the Forest Resources Council, School of Environmental and Resource Management, State University of New York College of Environmental Science and Forestry, Syracuse, New York 13210.     

Urea fertilization effects on nutrient uptake and growth of Platanus occidentalis during plantation establishment

Summary The benefit of fertilizer application during establishment of a tree plantation depends on effective nutrient uptake and the utilization of the nutrients in growth. Five urea treatments (0, 50, 75, 150, and 450 kg N/ha) were applied in a completely randomized plot design to a field planted with American sycamore (Platanus occidentalis L.) seedlings to evaluate growth responses and nitrogen use efficiency during the first season of plantation establishment. The site was in the Oak Ridge Reservation in eastern Tennessee on a highly weathered soil. Harvests were conducted on 3 occasions during a 22 week experimental period, and dry weights of stems, leaves, and large and small roots were measured. Chemical analyses were conducted on plant tissues from the 0, 75, and 450 kg N/ha treatments. Plant dry weight increased with urea application and growth analysis showed that this was mainly associated with increase in leaf area and to a minor extent with increase in net assimilation rate. Root weight increased significantly with urea application. The specific absorption rate of roots for several nutrients was greater at higher urea levels for the first 2 harvest periods, but this pattern reversed during the 3rd growth period. Surprisingly, manganese uptake and the specific absorption rate for manganese were enhanced with higher urea application. The acidifying effect of urea nitrification is a likely explanation for the increased Mn availability, and nitrate leaching and/or nitrogen immobilization contributed to low uptake of urea-N by the seedlings. The proportion of the applied nitrogen incorporated into the seedlings was 1.5 and 0.6% for the 75 and 450 kg N/ha urea treatments, respectively. Broadcast fertilizer application is not an effective way of supplying nutrients to seedlings during plantation establishment.     

Macro nutrient cation uptake by plants

Summary In pot experiments with barley, mustard, leek, lettuce and spinach, and in a field experiment with 30 cultivars of barley uptakes of K, Mg, Ca, Na and N were studied at varying concentrations and activities of these cations in the soil solution.The sum of macro cations (K, Mg, Ca, Na) in meq per 100 g aerial plant parts were independent of the chemical composition of the soil solution, but dependent on plant species and on the N concentration in the plant.The ratios of mean net inflows of Mg, Ca and K into plants and corresponding cation activity ratios (a_Mg/a_Ca and ) in the soil solution were linearly related and highly correlated under conditions in which growth rate and/or rate of incorporation into new tissues constituted the rate determining step of cation uptake. Consequently, mean net inflows of K, Mg and Ca were independent of ion concentration and ion activity of K, Mg or Ca in the soil solution under the conditions of constant activity ratio.The results agree with the concept that plants have a finite cation uptake capacity, and that plants are in a equilibrium-like state with the activities of K, Mg, and Ca ions in the soil solution. The results indicate that both ratios and content of exchangeable cations should be considered in our evaluation of soil test data.     

Modelling the interacting effects of nutrient uptake, light capture and temperature on phytoplankton growth

A model of phytoplankton growth developed by analogy with chemicalkinetics (CR model) in Baird and Emsley (J. Plankton Res., 21,85–126, 1999) is explored further. The CR model parameterizesall biochemical reactions involved in phytoplankton growth byone parameter: the maximum growth rate. Phytoplankton growthrate is then calculated from an interaction of the maximum growthrate, and the physical limit to extracellular nutrient uptakerates and light capture. In this paper, the CR model was re-derived,with two corrections and a number of modifications to increaseits generality. During derivation, the model's behaviour wascompared with chemostat cultures at a variety of dilution rates,nutrient inputs and temperatures. Model output was then plottedagainst observations of a semi-continuous culture of Isochrysisgalbana. Finally, the CR model was used to predict the growthrate of phytoplankton communities extracted from two temperatelakes under varying nutrient, light and temperature regimes.The CR model explained 37% of the variability of phytoplanktongrowth rate in cultures at environmental conditions similarto those of the lakes, compared with 25% explained by a non-linearbest fit to 324 growth experiments. The following paper in thisissue develops the CR model further, using it to predict stablecarbon isotope fractionation.     

Vitrification of rat embryos at various developmental stages

The effect of developmental stage on the survival of cryopreserved rat embryos was examined. Wistar rat embryos at various developmental stages were vitrified by a 1-step method with EFS40, an ethylene glycol-based solution, or by a 2-step method with EFS20 and EFS40. After warming, the survival of the embryos was assessed by their morphology, their ability to develop to blastocysts (or expanded blastocysts for blastocysts) in culture, or their ability to develop to term after transfer. Most (91-100%) of the embryos recovered after vitrification were morphologically normal in all developmental stages. However, the developmental ability of 1-cell embryos was quite low; exposing them to EFS40 for just 0.5 min decreased the in vitro survival rate from 76 to 9%. The survival rates of 2-cell embryos and blastocysts, both in vitro and in vivo, were significantly higher with a 2-step vitrification process than with a 1-step vitrification process. Very high in vitro survival rates (94-100%) were obtained in 4- to 8-cell embryos and morulae in the 1-step method. Although survival rates in vivo of 4-cell (40%) and 8-cell (4%) embryos vitrified by the 1-step method were comparatively low, the values were similar to those obtained in non-vitrified fresh embryos. When morulae vitrified by the 1-step method were transferred to recipients, the in vivo survival rate (61%) was high, and not significantly different from that of fresh embryos (70%). These results show that rat embryos at the 2-cell to blastocyst stages can be vitrified with EFS40, and that the morula stage is the most feasible stage for embryo cryopreservation in this species.     

Endocytosis of EGF-receptor complexes at various cell cycle stages

Parameters of EGF-receptor complex endocytosis have been studied in the early and late G1 phase and in mitosis. As a model, mouse mammary epithelial cells HC11 were used, whose growth depends on EGF presence in the medium. The Scatchard analysis has demonstrated that the surface receptors are represented by two receptor populations: 4800 high affinity (KD = 10(-11) M) receptors, and 73,000 low affinity (KD = 4.10(-9) M) receptors. Incubation of cells with the growth factor (5 ng/ml) resulted in a decrease in 125I-EGF binding, with its level being low until entering the S-phase. Under these conditions, receptors disposed on the plasma membrane presented a homogeneous population (KD = 8.10(-11) M, 14,000 receptors per cell). No reliable difference was revealed between the EGF-receptor complexes, internalized in early and late G1 phases, in respect to the internalization rate, level of recycling, degradation, and dynamics of compartmentalization. However, endocytosis of EGF-receptor complexes was found to be completely blocked in mitosis at the stage of internalization.     

Inorganic polyphosphate functions at various stages of cell evolution

An important property of all chemical components of the living cells is their polyfunctionality.However, the complex of their functions may significantly change in the process of evolution. This can be well illustrated by the example of polyphosphates. In procaryotes, polyphosphates are involved in many biochemical and physiological processes and their metabolic regulation. Their metabolism is first closely connected with adenyl metabolism and bioenergetics. In the lower eucaryotes, the cells of which are evidently of endosymbiotic origin, polyphosphate metabolism of various organelles is considerably different and closely connected with the specificity of their function. In these organisms, polyphosphates are involved in metabolic and probably in genetic regulation of phosphate and adenyl metabolism. However, they first play the role of an osmotically inert reserve of inorganic phosphorus. In the higher animals having the hormonal and nervous systems of cell metabolism regulation, the function of polyphosphates as a metabolic regulator disappears. However, they apparently still function as regulators of gene expression and some transport processes.     

Effects of nutrient recycling by zooplankton and fish on phytoplankton communities

In laboratory experiments we tested the hypothesis that nutrients supplied by fish and zooplankton affect the structure and dynamics of phytoplankton communities. As expected from their body size differences, fish released nutrients at lower mass-specific rates than Daphnia. On average, these consumers released nutrients at similar N:P ratios, although the ratios released by Daphnia were more variable than those released by fish. Nutrient supply by both fish and Daphnia reduced species richness and diversity of phytoplankton communities and increased algal biomass and dominance. However, nutrient recycling by fish supported a more diverse phytoplankton community than nutrient recycling by Daphnia. We conclude that nutrient recycling by zooplankton and fish have different effects on phytoplankton community structure due to differences in the quality of nutrients released. Received: 21 December 1998 / Accepted: 31 May 1999     

Uptake of sorbitol by chick embryo heart cells at various stages of development.

Sorbitol enters chick embryo heart cells from five days of development on. The rate of sorbitol entry becomes slower as development proceeds and the data suggest this is principally due to an increase in the apparent Km of transport, the Vmax remaining relatively constant. The uptake of sorbitol displays saturation kinetics and is believed on this ground to be carrier-mediated. Sorbitol does not appear to be actively transported since it is not concentrated against a gradient and its uptake is not inhibited by iodoacetate or 2, 4-dinitrophenol. Sorbitol does not appear to be taken up via the glucose transport system since uptake is not stimulated by insulin or inhibited by glucose or phloretin.     

Vitrification of mouse embryos at various stages by open-pulled straw (OPS) method

This study was performed to pursue the optimal condition for the cryopreservation of mouse morulae by a two-step OPS method and to investigate the feasibility of the optimal condition for vitrification of embryos at other developmental stages. First, the mouse morulae were vitrified in OPS using one-step procedure-that is, embryos were vitrified after direct exposure to EDFS30 (15% ethylene glycol (EG), 15% dimethyl sulfoxide (DMSO), Ficoll and sucrose), or two-step method-that is, embryos were first pretreated in 10%E + 10%D (10% EG and 10% DMSO in mPBS) for 30 sec, then exposed to EDFS30 for 15 to 60 sec, respectively. After vitrification and warming, the embryos were morphologically evaluated and assessed by their development to blastocysts, expanded/hatched blastocysts, or to term after transfer. The result showed that all the vitrified-warmed morulae had similar blastocyst rate compared to that of control (91.7% vs. 100%), and the highest developmental rate to expanded blastocysts (100%) or hatched blastocysts (62.3%) was observed when the morulae were pretreated with 10%E + 10%D for 0.5 min, exposed to EDFS30for 25 sec before vitrification and warming in 0.5 M sucrose for 5 min. After transfer, the survival rate (33.1%) in vivo of the vitrified morulae was higher (P > 0.05) than that of the fresh embryos (24.6%). Secondly, embryos at different stages were cryopreserved and thawed following the above program. Most (93.4 to 100%) of the embryos recovered after vitrification were morphologically normal at all the developmental stages. The blastocyst rates of the vitrified one-cell (52.5 to 66.7%) and the two-cell (63.3 to 68.9%) embryos were lower (P < 0.05) than those of the vitrified four-cell embryos (81.7 to 86.4%), the eight-cell embryos (90.0 to 93.3%), morulae (96.7 to 100%), and the expanded blastocysts rate (98.3 to 100.0%) of the vitrified early blastocysts. The highest survival rate in vivo of vitrified embryos were from the early blastocysts (40.4%), which was similar to that of fresh embryos (48.6%). The data demonstrate that the optimal protocol for the cryopreservation of morulae was suitable for the four-cell embryos to early blastocyst stages and that the early blastocyst stage is the most feasible stage for mouse embryo cryopreservation under our experimental conditions.