Electrophoretic detection of reversible chlorpromazine · HCl binding at the human erythrocyte surface

The binding of chlorpromazine · HCl at the human erythrocyte surface has been detected through its effect on cellular electrophoretic mobility. Incubation of erythrocytes (approx. 5 · 10⁶/ml) in 23 μM chlorpromazine · HCl resulted in a reduction of negative electrophoretic mobility from the control value of $\text{?1.11 ± 0.01}$ (μm · s^?1)/(V · cm^?1) to $\text{?1.00 ± 0.02}$ (μm · s^?1)/(V · cm^?1) (pH 7.2, ionic strength 0.155). This mobility change was completely reversed when chlorpromazine · HCl was removed by centrifugal washing. Increasing the drug concentration to 70μM did not affect the mobility change, indicating saturation of the electrophoretically detectable drug binding sites over chlorpromazine · HCl concentration range studied here. The effect of the 23 μM chlorpromazine · HCl on electrophoretic mobility was also measured in isotonic media of reduced ionic strength. The drug-induced reduction in negative surface charge density was found to be independent of ionic strength over the range 0.155 (Debye length, 0.8 nm) to 0.00310 (Debye length, 5.7 nm).Fixation of erythrocytes with glutaraldehyde affected neither the normal electrophoretic mobility of discocytes nor the reduced electrophoretic mobility of chlorpromazine · HCl-induced stomatocytes. When these stomatocytes were first fixed with glutaraldehyde, then washed free of chlorpromazine · HCl, they retained the stomatocyte form while regaining a normal control electrophoretic mobility. Conversely, when discocytes fixed in that form were treated with chlorpromazine · HCl, they showed the same mobility change as did fixed or unfixed stomatocytes. The drug-induced mobility change is therefore independent of the shape change, but reflects a contribution to cellular surface charge density from the membrane-bound chlorpromazine · HCl molecules. From the charge reduction, it is estimated that about 10⁶ chlorpromazine · HCl molecules are bound at the electrokinetic cell surface and occupy approximately 0.4% of the total surface area.     

Surface charge and cell volume of synchronized mouse lymphoblasts (L5178-Y)

Cellular electrophoretic mobility, and therefore, surface charge/ unit area, was found to be constant throughout the cell cycle of synchronized L5178-Y mouse lymphoblasts, remaining at – 1.21 μ sec^?1 V^?1 cm. Measured cell volumes of these synchronized cells increased linearly over the cell cycle and at mitosis each cell divided into two cells, each cell having half of the parent volume. An hypothesis is presented which explains the presence of a mobility peak at mitosis in cells which normally are grown attaching to a glass surface on the basis of differential morphological changes during mitosis; cells such as the L5178-Ys, which do not attach to glass normally, do not undergo such morphological changes at mitosis and, therefore, would not demonstrate a mobility peak at that time.     

Surface Anionic Groups in Symbiote-Bearing and Symbiote-Free Strains of Crithidia deanei1

The surface anionic groups of symbiote-bearing and symbiote-free strains of Crithidia deanei were compared by determining cellular electrophoretic mobility, by ultrastructural cytochemistry, and by identification of sialic acids by thin-layer and gasliquid chromatography. Symbiote-free Crithidia deanei has a highly negative surface charge (-0.9984 μm?s^-1? V^-1? cm), which is slightly reduced (-0.8527 μm?s^-1? V^-1? cm) by the presence of the endosymbiote. Treatment of both strains of C. deanei with neuraminidase decreased significantly the electrophoretic mobility of cells toward the cathodic pole, indicating the existence of exposed sialic acid residues responsible for the negative charge on the protozoan cell surface. Thin-layer and gas-liquid chromatography showed that N-glycolyl- and N-acetylneuraminic acids were present in both strains of C. deanei.     

EFFECTS OF HARVEST STAGE AND LIGHT ON THE BIOCHEMICAL COMPOSITION OF THE DIATOM THALASSIOSIRA PSEUDONANA1

The marine diatom Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal was cultured under three different light regimes: 100 μmol photon · m^?2· s^?1 on 12:12 h light : dark (L:D) cycles; 50 μmol photon · m^?2· s^?2 on 24:0 h L:D; and 100 μmol photon · m^?2· s^?1 on 24:0 h L:D. It was harvested during logarithmic and stationary phases for analysis of biochemical composition. Across the different light regimes, protein (as % of organic weight) was highest in cells during logarithmic phase, whereas carbohydrate and lipid were highest during stationary phase. Carbohydrate concentrations were most affected by the different light regimes; cells grown under 12:12 h L:D contained 37–44% of the carbohydrate of cells grown under 24:0 h L:D. Cells in logarithmic phase had high proportions of polar lipids (79 to 89% of total lipid) and low triacylglycerol (≤10% of total lipid). Cells in stationary phase contained less polar lipid (48 to 57% of total lipid) and more triacylglycerol (22 to 45% of total lipid). The fatty acid composition of logarithmic phase cells grown under 24:0 h L:D were similar, but the 100 μmol photon · m^?2· s^?1 (12:12 h L:D) cells at the same stage contained a higher proportion of polyunsaturated fatty acids (PUFAs) and a lower proportion of saturated and monounsaturated fatty acids due to different levels of 16:0, 16:1(n-7), 16:4(n-1), 18:4(n-3), and 20:5(n-3). With the onset of stationary phase, cells grown at 100 μmol photon · m^?2· s^?1 (both 12:12 and 24:0 h L:D) increased in proportions of saturated and monounsaturated fatty adds and decreased in PUFAs. Concentrations (% organic or dry weight) of 14:0, 16:0, 16:1(n-7), 20:5(n-3), and 22:6(n-3) increased in cells of all cultures during stationary phase. The amino acid compositions of cells were similar irrespective of harvest stage and light regime. For mariculture, the recommended light regime for culturing T. pseudonana will depend on the nutritional requirements of the animal to which the alga is fed. For rapidly growing bivalve mollusc larvae, stationary-phase cultures grown under a 24:0 h L:D regime may provide more energy by virtue of their higher percentage of carbohydrate and high proportions and concentrations of energy-rich saturated fatty acids.     

Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding dissolved inorganic nitrate uptake in Saccharina latissima and Laminaria digitata (Phaeophyceae)

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds Saccharina latissima and Laminaria digitata (Phaeophyceae) using a “pulse‐and‐chase” assay under fully controlled laboratory conditions. In a subsequent second “pulse‐and‐chase” assay, internal storage capacity (ISC) was calculated based on V_M and the parameter for photosynthetic efficiency F_v/F_m. Sporophytes of S. latissima showed a V_S of 0.80 ± 0.03 μmol · cm^?2 · d^?1 and a V_M of 0.30 ± 0.09 μmol · cm^?2 · d^?1 for dissolved inorganic phosphate (DIP), whereas V_S for DIN was 11.26 ± 0.56 μmol · cm^?2 · d^?1 and V_M was 3.94 ± 0.67 μmol · cm^?2 · d^?1. In L. digitata, uptake kinetics for DIP and DIN were substantially lower: V_S for DIP did not exceed 0.38 ± 0.03 μmol · cm^?2 · d^?1 while V_M for DIP was 0.22 ± 0.01 μmol · cm^?2 · d^?1. V_S for DIN was 3.92 ± 0.08 μmol · cm^?2 · d^?1 and the V_M for DIN was 1.81 ± 0.38 μmol · cm^?2 · d^?1. Accordingly, S. latissima exhibited a larger ISC for DIP (27 μmol · cm^?2) than L. digitata (10 μmol · cm^?2), and was able to maintain high growth rates for a longer period under limiting DIP conditions. Our standardized data add to the physiological understanding of S. latissima and L. digitata, thus helping to identify potential locations for their cultivation. This could further contribute to the development and modification of applications in a bio‐based economy, for example, in evaluating the potential for bioremediation in integrated multitrophic aquacultures that produce biomass simultaneously for use in the food, feed, and energy industries.     

THF INFLUENCE OF IRRADIANCE ON THF BIOCHEMICAL COMPOSITION OF THE PRYMNESIOPHYTE ISOCHRYSIS SP. (CLONE T-ISO)1

The effects of irradiance on the biochemical composition of the prymnesiophyte microalga, Isochrysis sp. (Parke; clone T-ISO), a popular species for mariculture, were examined. Cultures were grown under a 12:12 h light: dark (L:D) regime at five irradiances ranging from 50 to 1000 μE·m ²·s^?1 and harvested at late-logarithmic phase for analysis of biochemical composition. Gross composition varied aver the range of irradiances. The highest levels of protein were present in cells from cultures grown at 100 and 250 μE·m ³·s¹, and minimum levels of carbohydrate and lipid occurred at 50 μE·m^?2·s^?1. Because the cell dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Protein percentages were highest at Wand 100 μE·m^?2·s^?1 and carbohydrate at 100 μE·m^?2·s^?1. The composition of amino acids did not differ over the range of irradiances. Glutamate and aspartate were always present in high proportions (9.0–13.5%); histidine. methionine, tryptophan, cystine, and hydroxy-proline were minor constituents (0.0–2.6%). Glucose was the predominant sugar in all cultures, ranging from 23.0% (50 μE·m^?2·s^?1) to 45.0% (100 μE·m^?2·s^?1) of total polysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class components and fatty acids showed little change with irradiance. The main fatty acids were 14:0, 16:0, 16:1(n-7), 18:1(n-9), 18:3(n-3). 18:4(n-3), 18:5(n-3), and 22:6(n-3). Proportions of 22: 6(n-3) increased, whereas l8:3(n-3). 18:3(n-6). and 18:4(n-3) decreased, with increasing irradiance. Pigment concentrations were highest in cultures grown at 50 μE·m^?2·s^?1, except for fucoxanthin and diadinoxanthin (100 μE·m^?2·s^?1). The concentrations of accessory pigments correlated with chlorophyll a, which decreased in concentration with increasing irradiance. On the basts of biochemical composition, an irradiance of 100 μE·m^?1·s^?1 (12:12 h L:D cycle)for the culture of Isochrysis sp. (clone T-ISO) may provide optimal nutritional value for maricultured animals, although feeding trials are now necessary to substantiate this.     

CRITICAL IRRADIANCE LEVELS AND THE INTERACTIVE EFFECTS OF QUANTUM IRRADIANCE AND DOSE ON GAMETOGENESIS IN THE GIANT KELP,MACROCYSTIS PYRIFERA1

Gametophytes of Macrocystis pyrifera (L.) C. Ag. were cultured under a series of quantum irradiances in three photoperiod regimes. The quantum irradiances in each photoperiod were adjusted to provide equal daily irradiation dosages between photoperiods which allowed a critical examination of the interactions between quantum irradiance and quantum dose in determining gametophyte fertility. The lowest quantum irradiance which stimulated gametogenesis in more than 50% of the female gametophytes was 5 μE·m^?2·s^?1. The saturating irradiance was ca. 10 μE·m^?2·s^?1 at photoperiods of 12 h or greater. In terms of daily quantum dose, the lowest dose at which greater than 50% gametogenesis occurred was 0.2 E·m^?2·d^?1. However, this critical quantum dose was higher (0.4 E·m^?2·d^?1) when instantaneous irradiances were less than 5 μE·m^?2·s^?1. The saturation quantum dose was also affected by the rate at which the quantum dose was received and varied from 0.4 to 0.8 E·m^?2·d^?1. Gametophytes in all three photoperiods reached 100% fertility at quantum irradiances above 5 μE·m^?2·s^?1. Photoperiod effects were small and could be accounted for by quantum dosage effects.     

Simple oscillations in photosynthesis of higher plants

Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO₂ uptake and O₂ evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O₂. The minimum CO₂ concentration required for the appearance of oscillations was 600 μl · l^?1. The higher the CO₂ concentration, the stronger the oscillations. The effect of CO₂ concentration was saturated at 1000 μl CO₂ · l^?1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm^?2 · s^?1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm^?2 · s^?1. Oscillations could also be generated by increasing the CO₂ concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C₃ plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C₄ plants, Zea mays and Amaranthus retroflexus L.     

The charge mobilities in fused ring Oligothiophenes and their derivatives: influence of molecular structures

Fused ring oligothiophenes and their derivatives, as active organic semiconductors, are widely used in electronic devices. The influence of molecular conjunction length on reorganization energy, electronic coupling and charge mobility of two fused ring oligothiophenes are investigated theoretically. The charge mobility of 2, 5-di(thiophen-2-yl)thieno [3, 2-b]thiophene (T?T²?T) with longer molecular conjunction length is 0.226 cm²V^?1s^?1, which is nearly 3 times larger than that of 2, 2-bithieno[3, 2-b]thiophene (T²?T²) as 0.085 cm²V^?1s^?1. The investigation will provide a new perspective to design high mobility organic semiconductors.     

Dynamic responses of photosystem II and phycobilisomes to changing light in the cyanobacterium Synechococcus sp. PCC 7942

We have examined the molecular and photosynthetic responses of a planktonic cyanobacterium to shifts in light intensity over periods up to one generation (7 h). Synechococcus sp. PCC 7942 possesses two functionally distinct forms of the D1 protein, D1∶1 and D1∶2. Photosystem II (PSII) centers containing D1∶1 are less efficient and more susceptible to photoinhibition than are centers containing D 1∶2. Under 50 μmol photons· m^?2·s^?1, PSII centers contain D1∶1, but upon shifts to higher light (200 to 1000 μmol photons·m^?2·s^?1), D1∶1 is rapidly replaced by D 1∶2, with the rate of interchange dependent on the magnitude of the light shift. This interchange is readily reversed when cells are returned to 50 μmol photons·m^?2·s^?1. If, however, incubation under 200 μmol photons·m^?2·s^?1 is extended, D1∶1 content recovers and by 3 h after the light shift D1∶1 once again predominates. Oxygen evolution and chlorophyll (Chl) fluorescence measurements spanning the light shift and D1 interchanges showed an initial inhibition of photosynthesis at 200 μmol photons·m^?2·s^?1, which correlates with a proportional loss of total D1 protein and a cessation of growth. This was followed by recovery in photosynthesis and growth as the maximum level of D 1∶2 is reached after 2 h at 200 μmol photons·m^?2·s^?1. Thereafter, photosynthesis steadily declines with the loss of D1∶2 and the return of the less-efficient D1∶1. During the D1∶1/D1∶2 interchanges, no significant change occurs in the level of phycocyanin (PC) and Chl a, nor of the phycobilisome rod linkers. Nevertheless, the initial PC/Chl a ratio strongly influences the magnitude of photo inhibition and recovery during the light shifts. In Synechococcus sp. PCC 7942, the PC/Chl a ratio responds only slowly to light intensity or quality, while the rapid but transient interchange between D1∶1 and D 1∶2 modulates PSII activity to limit damage upon exposure to excess light.     

Voltage dependent potassium fluxes and the significance of action potentials in Acetabularia

Membrane potential, V_m, and K⁺(⁸⁶Rb⁺) fluxes have been measured simultaneously on individual cells of Acetabularia mediterranea. During resting state (resting potential approx. ?170 mV) the K⁺ influx amounts to 0.24–0.6 pmol · cm^?2 · s^?1 and the K⁺ efflux to 0.2–1.5 pmol · cm^?2 s^?1. According to the K⁺ concentrations inside and outside the cell (40 : 1) the voltage dependent K⁺ flux (zero at V_m = E_K = ?90 mV) is stimulated approx. 40-fold for V_m more positive than E_K.It is calculated that during one action potential (temporary depolarization to V_m more positive than E_K) a cell looses the same amount of K⁺, which leaks in during 10–20 min in the resting state (V_m = ?170 mV). Since action potentials occur spontaneously in Acetabularia, they are therefore suggested to have a significant function for the K⁺ balance of this alga.     

Relationships between irradiance and photosynthesis for marine benthic green algae (Chlorophyta) of differing morphologies

Photosynthesis-irradiance relationships were determined in the field for five species of littoral and shallow sublittoral marine benthic green algae (Chlorophyta) of differing morphologies. Each species exhibited a linear increase in photosynthetic rate with increasing irradiance up to a maximum light-saturated value. Full sunlight (1405 to 1956 μE·m^?2·s^?1) inhibited photosynthesis of all species except the thick, optically dense, Codium fragile (Sur.) Har. Compensation irradiances ranged from 6.1 μE·m^?2·s^?1 for Enteromorpha intestinalis (L.) Link to 11.4 μE·m^?2·s^?1 for Ulva lobata (Kütz) S. & G. and did not reveal a consistent relationship to seaweed morphology. Saturation irradiances were determined statistically (I_k) and visually from graphical plots. with the latter technique resulting in values three to eight times higher and different comparative rankings of species than the former. I_k saturation irradiances were highest for Chaetomorpha linum (Müll.) Kütz. (81.9 μE·m^?2·s^?1) and lowest for Codium fragile (49.6 μE·m^?2·s^?1) and did not reveal a relationship with seaweed morphology. Regression equations describing light-limited photosynthetic rates and the relative magnitudes of the maximal net photosynthetic responses both strongly suggested a relationship with seaweed morphology. Highest net photosynthetic rates were obtained for the thin, sheet-like algae Ulva lobata (9.2 mg C·g dry wt^?1·h^?1), U. rigida C. Ag. (6.5 mg C·g dry wt^?1·h^?1) and the tubular form, Enteromorpha intestinalis (7.3 mg C·g dry wt^?1·h^?1), while lowest rates occurred for Codium fragile (0.9 mg C·g dry wt^?1·h^?1). Similarly, steepest light-limited slopes were found for the algae of simpler morphology, while the most gradual slope was determined for Codium fragile, the alga with greatest thallus complexity.     

A SIMPLE METHOD FOR ISOLATING FILAMENTS AS “ALGAL SEED STOCK” FROM MONOSTROMA LATISSIMUM (CHLOROPHYTA) GERMLINGS,AND APPLICATION FOR MASS CULTIVATION1

Germlings were grown from Monostroma latissimum Wittr. reproductive cells on nylon ropes. Holdfast threads and some uniseriate filaments were observed to have penetrated the fibers of the dispersed ropes. The algal filaments were easily isolated and prepared for cultivation, in comparison to the methods of enzymatically isolated algal protoplasts. Under low light (60–100 μmol photons · m^?2 · s^?1), the algal filaments grew to form a filamentous mass. When cultivated under stronger light (300–600 μmol photons · m^?2 · s^?1), they grew to initially form tubular thalli and then, when cultivated under light intensities >700 μmol photons · m^?2 · s^?1, formed foliaceous thalli. Consequently, the filaments were homogenized into small sections and then sewed on the nylon rope for algal mass cultivation. Under high‐intensity natural light, they grew to form leafy thalli.     

CRITICAL LEVELS OF LIGHT AND TEMPERATURE REGULATING THE GAMETOGENESIS OF THREE LAMINARIA SPECIES (PHAEOPHYCEAE)1

Gametophytes of three Laminaria species occurring near Helgoland, North Sea, were cultivated 4 wk in a 12:12 LD regime at different temperatures in artificial light fields, and in the sea at different water depths. In the artificial light fields underwater spectral distribution was simulated according to Jerlov water Types 5, 7, 9. Blue light in the simulated light fields amounted to 17, 12 or 4% of total quanta. The rate of vegetative growth did not depend on spectral distribution, was light-saturated at 4–6 W · m^?2, and increased with temperature up to 15 C. L. saccharina (L.) Lamour. exhibited the highest tolerance towards temperature, light and UV. Gametophytes survived 1 wk at 21 C ± 0.1, but not 22 C ± 0.1. Gametophytes of L. hyperborea (Gunn.) Fosl. and L. digitata (Huds.) Lamour. survived 1 wk at 20 C ± 0.1, but not at 21 C ± 0.1. In sunlight, and in the light field of a xenon lamp, 50% of L. saccharina gametophytes were killed by a quantum dose of 50 μEin · cm^?2, and 100% of the plants by 90 μEin · cm^?2. Approximately half of these quantum doses killed the corresponding percent of the other species gametophytes. Appreciably higher quantum doses were survived in visible light, with red being the most detrimental. Fertility depended on a critical quantum dose of blue light which decreased almost exponentially with decreasing temperature. The quantum dose (400–512 nm) required for induction of fertilization of 50% of the female gametophytes (males react similarly) was 90 μEin · cm^?2 at 5 C, 110 μEin · cm^?2 at 10 C, 230 (560 in L. digitata)μEin · cm^?2 at 15 C, and 560 (L. hyperborea) or about 850 (other 2 species) μEin · cm^?2 at 18 C. In the sea the gametophytes survived the dark winter months in the unicellular stage, with almost no vegetative growth of the primary cell, due to lack of light. In early spring the female gametophytes matured in the unicellular, and the males in a few-celled stage at the depth of 2 m, as did the laboratory cultures under conditions inducing maximal fertility.     

Chick kidney microsomal cytochrome P-450 involvement in the metabolism of 25-hydroxyvitamin D3

Suspensions of 2 to 5% rat thymocytes were incubated at 35 °C in buffered balanced salt solution (pH 7.3) with lactate and β-hydroxybutyrate as fuels. The dependence of 3-O-[Me-³H]methylglucose influx on external and internal 3-O-methylglucose concentrations was studied. Entry was almost rectilinear during the first minute. From the dependence of methylglucose entry (into sugar-free cells) on external methylglucose concentration, we judged the entry K_m to be about 7.7 mm and the entry V to be about 0.64 μmol · min^?1 · (ml of packed cell volume)^?1. Methylglucose inside the cell enhanced influx, hence equilibrium exchange was faster than entry. The dependence of equilibrium exchange on methylglucose concentration (inside and outside being equal) indicated a K_m of about 25 mm and a V of about 2.1 μmol · (min)^?1 · (ml of cell volume)^?1. This effect of internal sugar indicated that entry into sugar-free cells is limited mainly by the return of empty carrier to the outside surface and that loading the carrier on the inside enhances its outward mobility. The K_m and V for influx into cells containing 21 mm methylglucose were 5.9 mm and 1.17 μmol · min^?1 · (ml of packed cells)^?1. The effect of 21 mm internal sugar on lowering the influx K_m from about 7.7 mm to about 6 mm was reproducible and contributed to the evaluation of the constants of the transport rate law. It indicated that loading of the carrier at the external surface reduces its mobility, in contrast to the effect of loading on the inside. Mechanical explanations for this behavior are discussed.     

The Surface Charge of Tritrichomonas foetus

The surface charge of Tritrichomonas foetus was evaluated by means of the binding of colloidal iron hydroxide particles at pH 1.8 and cationized ferritin particles at pH 7.2 to the cell surface, as visualized by electron microscopy and by direct measurements of the electrophoretic mobility (EPM), of cells suspended in solutions of different ionic strength and pH. At pH 7.2, T. foetus has a negative surface charge with a mean EPM of ?1.03 μmμs^?1μV^?1μcm. At lower pH, there is a decrease in the negative surface charge with an isoelectric point at pH 1.2. At higher pH (> 9.0), there is an increase in the surface charge reaching an EPM of ?2.5 μmμs^?1μV^?1μcm. These results indicate that the surface of T. foetus contains both negatively and positively charged dissociating groups. Binding of colloidal iron hydroxide and cationized ferritin particles throughout the cell surface of the protozoon was observed. Treatment of T. foetus with neuraminidase or trypsin reduced significantly the EPM of the cells. Enzyme-treated cells recovered their normal EPM when incubated for 6 h in fresh culture medium by a process that is inhibited by puromycin.     

PHYSIOLOGICAL VARIATION AND ELECTROPHORETIC BANDING PATTERNS OF GENETICALLY DIFFERENT SEASONAL POPULATIONS OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Clones of Skeletonema costatum (Grev.) Cl. isolated from Narragansett Bay, R.I., during different seasons were grouped according to their electrophoretic banding patterns. The growth rates, pg chlorophyll · cell^?1, carbon uptake · cell^?1· h^?1, and carbon uptake · pg chl^?1· h^?1 were measured at 20°C, in a 14:10 h L:D cycle at 180 μE · m^?2· s^?1. Statistically significant sources of variation were found among groups of clones in growth rate, pg chl · cell^?1, and carbon uptake · pg chl^?1· h^?1. It was concluded that there is a significant relationship between the physiological characteristics of clones isolated from populations in different seasons and patterns of genetic variation inferred from the electrophoretic studies. However, genetic diversity detected by banding patterns tends to underestimate the total genetic diversity in natural populations. The groups of clones most common in summer bloom populations had significantly higher growth rates, lower values of pg chl · cell^?1, and higher rates of carbon uptake · pg chl^?1· h^?1 at 20°C than did the group of clones most common in winter bloom populations. However, differences among groups in these parameters at 20°C alone cannot account for the seasonal cycling of genetically variable populations of Skeletonema in Narragansett Bay. The range of growth rates among clones of this species is 0.1–5.0 divisions · d^?1 under a single set of temperature and light conditions. Chlorophyll concentrations range from 0.2–1.7 pg chl · cell^?1 and carbon uptake · pg chl^?1· h^?1 varies by a factor of 7 among clones. The range of physiological variation in this species means that it is difficult to use laboratory studies of single clones to analyze the responses of natural populations of Skeletonema.     

The yield of chlorophyll a fluorescence as a means to test the various deexcitation mechanisms in the antenna system of green plants

With the aid of measurements of the fluorescence yield, the efficiency of the various deexcitation mechanisms of an exciton in the light-harvesting system has been determined. For this purpose, the fluorescence of dark-adapted as well as of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-treated and preilluminated leaves of Zea mays L. was excited by single ultrashort laser pulses of different energies. The experimental results have served for the fitting of solutions of rate equations, which describe the deexcitation by linear relaxation processes like fluorescence and radiationless transitions, by annihiation of excitons, and by traps both in the ground state and in an excited state. We have obtained the following results: a ratio of antenna chlorophyll molecules to Photosystem II traps of 600:1, an annihilation constant γ = 2·10^?8 cm³·s^?1, a mean trapping time of $\text{t}\text{?}\text{=0.5}\text{ns}$, a trapping probability for traps in the ground state of 2·10^?8 cm³·s^?1, and 6·10^?9 cm³·s^?1 for traps in an excited state.     

Characterization of the uptake of sucrose and glucose by isolated seed coat halves of developing pea seeds. Evidence that a sugar facilitator with diffusional kinetics is involved in seed coat unloading

Uptake of ¹⁴C-labelled sucrose and glucose by isolated seed coat halves of pea (Pisum sativum L. cv. Marzia) seeds was measured in the concentration range <0.1 μM to 100 mM. The initial influx of sucrose was strictly proportional to the external concentration, with a coefficient of proportionality (k) of 6.2 μmol·(g FW)^?1·min^?1·M^?1. Sucrose influx was not affected by 10 μM carbonylcyanide m-chlorophenylhydrazone (CCCP), but it was inhibited by 40% in the presence of 2.5 mM p-chloromercuribenzenesulfonic acid (PCMBS). Influx with diffusional kinetics was also observed for glucose (k = 4.8 μmol·(g FW)^?1·min ^?1·M ^?1) and mannitol (k = 5.1 μmol·(g FW)^?1·min^?1·M^?1). For glucose an additional saturable system was found (K_m = 0.26 mM, V _max = 4.2 nmol·(g FW)^?1·min^?1), which appeared to be completely inhibited by CCCP and partly by PCMBS. In contrast to the diffusional pathway, uptake by this saturable system was slightly pH-dependent, with an optimum at pH 5.5. The influx of sucrose appears to be by the same pathway as the efflux of endogenous sucrose, which was inhibited by 36% in the presence of 2.5 mM PCMBS (De Jong A, Wolswinkel P, 1995, Physiol Plant 94: 78–86). It is argued that passive transport may be the only mechanism for sucrose transport through the plasma membrane of seed coat parenchyma cells. The estimated permeability coefficient of the plasma membrane for sucrose (P = 3.5·10^?7 cm·s^?1) is more than 1 × 10⁶-fold higher than that reported for artificial lipid membranes. This relatively high permeability is hypothesized to result from pore-forming proteins that allow the diffusion of sucrose. Furthermore, it is shown that a sucrose gradient across the plasma membrane of the seed coat parenchyma of only 22 mM will suffice to result in the net efflux of sucrose which is required to feed the embryo.     

Effects of Side Chains on Thiazolothiazole‐Based Copolymer Semiconductors for High Performance Solar Cells

New thiazolothiazole‐dithienosilole copolymer semiconductors bearing side chains of different type, size, and topology were synthesized and used to demonstrate the influence of side chains on morphology, charge transport and photovoltaic properties. The field effect mobility of holes varied from 0.01‐0.03 cm²V^?1s^?1 in PSOTT and PSEHTT to 0.12 cm²V^?1s^?1 in PSOxTT. The average power conversion efficiency of solar cells under 1.0 sun illumination could be varied from 2.1% in PSOxTT and 4.1% in PSOTT to 5.0% in PSEHTT. The highest photovoltaic efficiency achieved in PSEHTT, that has all‐branched alkyl side chains and face‐on π‐stacking orientation, was corroborated by its enhanced charge photogeneration observed by transient absorption spectroscopy.