David L. Correll

Relationship between phytoplankton cell size and the rate of orthophosphate uptake: in situ observations of an estuarine population

Orthophosphate uptake by a natural estuarine phytoplankton population was estimated using two methods: (1) 32P uptake experiments in which filters of different pore sizes were used to separate plankton size-fractions; (2) 33P autoradiography of phytoplankton cells. Results of the first method showed that plankton cells larger than 5 μm were responsible for 2% of the total orthophosphate uptake rate. 98% of the total uptake rate occurred in plankton composed mostly of bacteria, which passed the 5 μm screen and were retained by the 0.45 μm pore-size filter. There was no orthophosphate absorption by particulates in a biologically inhibited control containing iodoacetic acid. Orthophosphate uptake rates of individual phytoplankton species were obtained using 33P autoradiography. The sum of these individual rates was very close to the estimated rate of uptake by particulates larger than 5 μm in the 32P labelling experiment. Generally, smaller cells were found to have a faster uptake rate per μm3 biomass than larger cells. Although the nannoplankton constituted only about 21% of the total algal biomass, the rate of phosphate uptake by the nannoplankton was 75% of the total phytoplankton uptake rate. Results of the plankton autoradiography showed that the phosphate uptake rate per unit biomass is a power function of the surface: volume ratio of a cell; the relationship is expressed by the equation Y=2x10-11X1.7, where Y is μgP μm-3 h-1 and X is the surface: volume ratio. These results lend support to the hypothesis that smaller cells have a competitive advantage by having faster nutrient uptake rates.

Comparison of precipitation and land runoff as sources of estuarine nitrogen

Abstract The seasonal and year-to-year variation of bulk precipitation as a source of total N, nitrate and ammonia is reported for a 7-year period at the Rhode River, a subestuary of Chesapeake Bay, U.S.A. These values are placed in perspective by comparison with analogous nitrogen loading due to watershed discharges. Although year-to-year variations were important, in an average year about the same amount of readily available nitrogen entered the system via precipitation as entered in land runoff and, during the summer and fall, precipitation was the largest source.

Atrazine toxicity to submersed vascular plants in simulated estuarine microcosms

Abstract Photosynthesis in Potamogeton pectinatus L. and Zostera marina L. was inhibited by 650 μg 1 −1 of dissolved atrazine, but was stimulated by 75 μg 1 −1 . Photosynthesis in Zannichellia palustris L. was inhibited at both of these concentrations while in Vallisneria americana Michx inhibition was significant at the higher concentration but minor at the lower concentration. Atrazine at 120 μg 1 −1 in solution caused 100% mortality of Vallisneria within 30 days. At 12 μg 1 −1 mortality of Vallisneria was 50% after 47 days and the production of new plants at the ends of runners and leaf area increase of survivors were significantly reduced. Treatment with 3.2 μg 1 −1 had relatively minor effects and results from exposure to 1.3 μg 1 −1 were indistinguishable from controls. Data were also taken on the partitioning of atrazine between the abiotic phases in the microcosms and on rate of atrazine breakdown.

Phytochrome in etiolated annual rye: IV. Physical and chemical characterization of phytochrome

Abstract Isolated phytochrome was demonstrated to be free from all but trace impurities by high speed velocity and equilibrium ultracentrifugation, polyacrylamide electrophoresis, and gel filtration in Sephadex G-200. The results from these techniques and from electron microscopy, amino acid analyses, and tryptic peptide separations were consistent with the native phytochrome molecules existing as 14-S hexamers and 9-S tetramers of 2-S monomer units. The monomer unit appears to be chemically identical, existing as a single polypeptide chain of approx. 42 000 molecular weight. These monomer units appear to be associated through noncovalent type bonds. Fluorescence studies indicated that when the 660 nm-absorbing form of phytochrome was excited at 290 nm, it fluoresced intensely at 340 nm and slightly at 672 nm. When excited at 370 nm, it fluoresced at 672 nm.

Comparison of bacterial and algal utilization of orthophosphate in an estuarine environment

Bacterial utilization of orthophosphate in an estuarine environment has been differentiated from algal utilization by using flow-filters of 5.0, 1.2 and 0.45 μm poresize. Examination by light microscopy showed that most of the bacterial population passed through a 5.0-μm filter, whereas most algae were retained. In all experiments, bacterial and algal cell numbers and biomass were estimated. P-uptake by algae and bacteria was closely correlated with cell biomass. P-uptake by algae was high only in the summer months, whereas P-uptake by bacteria was high throughout the year. Neither algal nor bacterial P-uptake, however, was correlated with temperature or dissolved orthophosphate, total organic phosphate or total phosphate concentrations. Cell biomass of algae at a given time had a high correlation with dissolved organic phosphate levels in 2 weeks prior to sampling (r=0.830) and a low correlation in the 2 weeks following sampling (r=0.0005). Algal cell numbers had a high correlation with bacterial cell numbers (r=0.950). The biomass of algae and bacteria also had a high correlation (r=0.902). The rate of P-uptake from the water by algae and bacteria varied with season and with the species composition of the natural population.

Autoradiographic study to detect metabolically active phytoplankton and bacteria in the Rhode River estuary

The rate of utilization of inorganic carbon (C) and phosphate (P) by phytoplankton and bacteria in the Rhode River estuary has been estimated using liquid-emulsion autoradiography during four times of the year. Metabolic activity of phytoplankton was estimated by calculating silver grains above individual species. From these counts, the relative C and P uptake rates of individual species per unit of biomass and per volume of water were estimated. Examination of the autoradiograms showed that the metabolically most active, algae were smaller than 10 μm. Both C and P were paken up by these smaller species at a higher rate than their proportion of the total biomass per volume of water would indicate. Uptake of C and P per unit of cell volume varied within a species and among the various phytoplankton at the different seasons of the year. Metabolic activity of planktonic bacteria in safranin-stained autoradiograms was also estimated by counting bacteria with associated grains and cells without grains. The ratio of 33p-labeled to unlabeled bacteria was highest in November. This high metabolic activity of bacteria in November corresponded with high P uptake rates of the phytoplankton at that time. Throughout this study, only 28 to 42% of the total phytoplankton biomass was metabolically active and, 63 to 85% of the bacteria.

Phytochrome in etiolated annual rye III. Isolation of photoreversible phytochrome

Abstract An isolation procedure for phytochrome which includes only 5 major steps and can be carried to completion in 3 days is reported. All of the steps are adaptable to either smaller or larger scale operations. It is necessary for maximum yield to carry out the isolations under green safelights. A yield of about 300 mg of photoreversible phytochrome protein per 20 kg of initial plant material may be obtained. This represents about 25% of the photoactivity in the initial extract. The isolated phytochrome is stable in the dark at 2° for over 1 month. A prerequisite to the isolation of phytochrome is the selection of seeds which will yield seedlings with high levels of stable phytochrome. The photoactivity per mg of phytochrome isolated from such a selected lot of seeds, after progressively longer storage of the seeds, declined although the absorption spectra remained the same qualitatively. This loss was found to be due to a decrease in stability of the phytochrome chromophore. Experiments on the incorporation of radioactive amino acids indicated that the phytochrome isolated came from a preformed protein present in the dry seeds. It was concluded that the instability of phytochrome extracted from etiolated seedlings grown from stored seeds was due to damage incurred by the protein in storage. This protein damage would be likely to expose the chromophore to environmental stress during the isolation steps which would destroy its photoreversibility.

MULTIPLE CHROMOPHORE SPECIES IN PHYTOCHROME

Abstract— Buffered aqueous solutions of pure phytochrome, when irradiated at 730 nm, had a main absorption band at about 660 nm and a shoulder or secondary band at 580–600 nm. When irradiated at 660 nm, these absorption bands bleached and a pair of bands at 670 and 725–730 nm appeared. When 660 nm irradiated samples were placed in the dark the 730 nm absorption slowly bleached and the 670 nm absorption band shifted to 660 nm. The kinetics of the bleaching indicated that two populations of PFR existed initially. These two populations decayed by first order kinetics with ks of 4.8 × 10‐4 sec‐1 and 3.1 × 10‐‐5 sec‐1at 25°. While the bleaching of PFR was occumng, the appearance of the 660 nm and 580–600 nm absorption bands characteristic of PR took place. The kinetics of the increase in the 580 and 660 nm absorption bands indicated that it was arising from two populations of reactants by two first order reactions with ks of 6.4 × 10‐4 sec‐1 and 3.1 × 10‐5sec‐1 at 25°. When the sodium chloride concentration of the solvent was changed the proportions of the kinetically different populations were altered. In some conditions, especially in the presence of air. reversible but non‐reciprocal changes in the four absorption bands were observed. These effects were evident after the lapse of many hours in the dark. When native phytochrome was treated with sodium dodecyl sulfate all absorption bands but the 580–600 nm absorption band were bleached and photoreversibility was lost. When native phytochrome was treated with glutaraldehyde, the 730 nm absorption band was bleached but photoreversibility was retained. It was concluded that at least four species of chromophore exist in phytochrome with absorption maxima at 580, 660, 670 and 730 nm. Each chromophore is capable of being bleached by appropriate irradiation or in the dark by chemical reactions rather than photochemical reactions. The reactions are probably coupled redox reactions between the 580–660 nm pair and the 670–730 pair of chromophores. Discrepancies observed in the reciprocity of the absorption changes in these paired bands are probably due to various degrees of uncoupling and secondarily to the redox potential of the solvent when such uncoupling occurs.

Phytochrome in etiolated annual rye : I. Changes during growth in the amount of photoreversible phytochrome in the coleoptile and primary leaf.

SummaryDuring a seven-fold increase in length the content of the coleoptile in photoreversible phytochrome increased four-fold and that of the primary leaf nine-fold. The phytochrome content, during growth, expressed on a fresh- or dry-weight basis did not vary greatly for either organ. Phytochrome per mg dry weight (ΔOD730/mg=0.5) was nearly the same in the leaf as in the coleoptile. Coleoptiles studied had a constant DNA content of 4.1 μg per organ. DNA content of the leaf increased with age. Phytochrome per DNA was much higher in the coleoptile than in the primary leaf and increased with growth in each of these organs. Thus, there was not a constant amount of phytochrome per cell in either tissue with increasing age and there was not the same amount of phytochrome per cell in the coleoptile as in the primary leaf at any age.

Relationship of nitrogen discharge to land use on Rhode River watersheds

Abstract Eight Rhode River subwatersheds were monitored with flow volume-integrating apparatus for area yield discharge of total nitrogen, total kjeldahl nitrogen and nitrate nitrogen. Land use data for each subwatershed were also estimated from aerial photographs and ground truth surveys. Regression analyses of area yield discharge for the year versus percent managed land (row crops + pasture + residential) have high ( R 2 = 0.65−0.68) correlations for all three nitrogen parameters. Correlations were relatively high for nitrate nitrogen in each season; however, little relationship was found between percent disturbed land and total Kjeldahl nitrogen in the spring. Correlations were higher in five variable multiple linear regressions utilizing four land use categories. Nitrate nitrogen had a strong correlation with percent row crops, the highest correlation being in the winter and the lowest in the fall. Total Kjeldahl nitrogen had a high correlation with row crops in the summer when this form of nitrogen was discharged at high rates. Variations in percentages of four land use categories were sufficient to explain 98% of the variation between watersheds in discharges of total nitrogen for the year. High percentages of the variability in discharge of Kjeldahl and of nitrate nitrogen between watersheds were also explainable by land use variation for the year and for most season-parameter combinations. A second set of multiple linear regressions utilizing basin characteristics related to transport mechanisms resulted in generaly similar coefficients of determination for all three parameters.