Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean

Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of 1991–1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K ⁻¹ _par) and the satellite-weighted depth. The temporal variability was resolved every 2–3 days and was observed to be greater within years than between years. Three-year averages (n=223) revealed that 10.2 ± 3.6% of total Chl a and 14.8 ± 6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values were twice as high within K ⁻¹ _par, 24.1 ± 8% of total Chl a and 34 ± 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time scales of seasonal blooms. We observed that the patterns of Chl a vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within K ⁻¹ _par and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K ⁻¹ _par and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean, especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences. Accepted: 27 August 1999     

The impact of phytoplankton on spectral water transparency in the Southern Ocean: implications for primary productivity

Spectral water transparency in the Northern Weddell Sea was studied during Austral spring. The depth of the 1-% surface irradiance level (euphotic depth) varied between 35 and 109 m and was strongly influenced by phytoplankton biomass. Secchi depths were non-linearly related to euphotic depth. In phytoplankton-poor water, the most penetrating spectral region was restricted to a relatively narrow waveband in the blue (488 nm), but the range was broader, between 488 and 525 nm when phytoplankton were abundant. Water transparency in the red spectral range was always low and only to a small extent affected by phytoplankton. Two independent procedures were used to quantify the impact of phytoplankton on spectral water transparency: (1) Regression analysis of spectral in situ vertical light attenuation coefficients in the sea, against coincident chlorophyll concentrations. This method gave chlorophyll-specific light attenuation coefficients; the y-intercept could be interpreted as a measure of light attenuation by pure water plus non-algal material. (2) Spectra of in vivo light absorption derived by spectroscopy, using phytoplankton enriched to varying degrees onto filters. Thus chlorophyll-specific absorption cross-sections were determined. Estimates obtained by both procedures were in close agreement. By integrating over the spectrum of underwater irradiance, in situ chlorophyll-specific absorption cross sections of phytoplankton suspensions, related to all photosynthetically active radiation, were calculated. Light absorption by phytoplankton for photosynthesis is accomplished mainly in the blue spectral range. Also dissolved and particulate organic matter contributed to the attenuation of blue light. Because in water poor in phytoplankton, underwater irradiance was progressively restricted to blue light, chlorophyll-specific absorption cross-sections of phytoplankton, averaged over the spectrum of photosynthetically active irradiance, increased with water depth. In water with elevated phytoplankton biomass, overall light attenuation was generally enhanced. However, because the spectral composition of underwater light changed relatively little with depth, except immediately below the water surface, light absorption cross-sections of phytoplankton changed little below 10 m depth. Vertical differences in the proportions of underwater light absorbed by the phytoplankton community here were mainly dependent on biomass variations. Because of the comparatively small attenuation of blue light by non-algal matter, the efficiency of light harvesting by phytoplankton at any given concentration of chlorophyll in Antractic waters is greater than in other marine regions. At the highest phytoplankton biomass observed by us, as much as 70% of underwater light was available for phytoplankton photosynthesis. When phytoplankton were scarce, <10% of underwater light was harvested by phytoplankton.Contribution within the European Polarstern Study (EPOS), supported by the Deutsche Forschungsgemeinschaft, Grant Ti 115/16-1 to MMT, the European Science Foundation, and by the Alfred Wegener Institut für Polar-und Meeresforschung, Bremerhaven     

On the compatibility of carbon uptake rates calculated from stable and radioactive isotope data: implications for the design of experimental protocols in aquatic primary productivity

Basic differences between the ¹³C and the ¹⁴C techniques ofmeasuring carbon uptake by phytoplankton exist at the levelof the isotopic analysis. With the first method, a ratio ofisotopic abundances is measured on the sample, whereas an absoluteamount of isotope is estimated with the second method. If acarbon source other than the labeled one is utilized by thephytoplankton during incubation, the stable isotope method maybe biased. Specific uptake values will be underestimated bythis effect. It is, however, possible to obtain unbiased estimatesof the ¹³C-labeled carbon uptake by using an equation containinga term describing the final particulate carbon concentration.Only under this condition will carbon uptake rates derived from¹³C isotope data be always compatible with the ¹³C method ofmeasuring primary production ^*This paper is the result of a study made at the Group for AquaticPrimary Productivity (GAP), Second International Workshop heldat the National Oceanographic Institute, Haifa, Israel in April–May1984.     

Sequence variation at cpDNA regions of watermelon and related wild species: implications for the evolution of Citrullus haplotypes

Sequencing analysis of one coding and four noncoding cpDNA regions was conducted to infer biogeographic and evolutionary relationships in the genus Citrullus. Eighteen taxa from diverse geographical areas were included. A low number of parsimony informative characters (1.1%) was observed at the ～4 kb section of cpDNA. Variability within Citrullus was detected primarily at noncoding regions of high A + T content. Substitution rates varied from 0-0.48% for ndhF with A + T content of 68.4% to 0.39- 1.69% for the intergenic region of atpA with A + T content of 82.8%, mainly resulting in indels and transversions. Indels at several regions acted as valuable parsimony informative markers. Citrullus lanatus var. lanatus, the cultivated watermelon, and C. ecirrhosus and C. rehmii from Namibia, lacked molecular variability. The genus Citrullus is supported monophyletically and shows two main clades, one of which contains C. colocynthis. In the other clade, C. rehmii is sister to a clade containing C. ecirrhosus and C. lanatus. Two clades were recovered within C. lanatus, consisting of domesticated watermelon and wild citron, var. citroides. Five haplotypes within C. colocynthis were used to deduce colonization routes of the species. Biogeographic patterns point to separate colonization events into Africa and the Far East.     

Alterations in the production and concentration of selected alkaloids as a function of rising atmospheric carbon dioxide and air temperature: implications for ethno-pharmacology

The influence of recent and projected changes in atmospheric carbon dioxide concentration [CO₂] with and without concurrent increases in air temperature was determined with respect to growth characteristics and production of secondary compounds (alkaloids) in tobacco (Nicotiana tabacum L.) and jimson weed (Datura stramonium L.) over a ca. 50‐day period. Rising [CO₂] above that present at the beginning of the 20th century resulted in consistent, significant increases in leaf area, and above ground dry weight (both species), but decreased leaf area ratio (LAR) and specific leaf area (SLA) in jimson weed. Increased temperature resulted in earlier development and increased leaf area for both species, but increases in above ground final dry weight were observed only for jimson weed. The secondary compounds evaluated included the alkaloids, nicotine, atropine and scopolamine. These compounds are generally recognized as having impacts with respect to herbivory as well as human physiology. Rising [CO₂] reduced the concentration of nicotine in tobacco; but had no effect on atropine, and increased the concentration of scopolamine in jimson weed. However, because of the stimulatory effect of [CO₂] on growth, the amount of all three secondary compounds increased on a per plant basis in both species. Temperature per se had no effect on nicotine or scopolamine concentration, but significantly increased the concentration and amounts of atropine per plant. Overall, the underlying mechanism of CO₂ induced changes in secondary compounds remains unclear; however, these data suggest that the increase in [CO₂] and temperature associated with global climate change may have significant effects not only with respect to herbivory, but on the production of secondary compounds of pharmacological impact.     

High rates of net primary production and turnover of floating grasses on the Amazon floodplain: implications for aquatic respiration and regional CO2 flux

We investigated whether rates of net primary production (NPP) and biomass turnover of floating grasses in a central Amazon floodplain lake (Lake Calado) are consistent with published evidence that CO₂ emissions from Amazon rivers and floodplains are largely supplied by carbon from C4 plants. Ground‐based measurements of species composition, plant growth rates, plant densities, and areal biomass were combined with low altitude videography to estimate community NPP and compare expected versus observed biomass at monthly intervals during the aquatic growth phase (January–August). Principal species at the site were Oryza perennis (a C3 grass), Echinochloa polystachya, and Paspalum repens (both C4 grasses). Monthly mean daily NPP of the mixed species community varied from 50 to 96 g dry mass m^?2 day^?1, with a seasonal average (±1SD) of 64±12 g dry mass m^?2 day^?1. Mean daily NPP (±1SE) for P. repens and E. polystachya was 77±3 and 34±2 g dry mass m^?2 day^?1, respectively. Monthly loss rates of combined above‐ and below‐water biomass ranged from 31% to 75%, and averaged 49%. Organic carbon losses from aquatic grasses ranged from 30 to 34 g C m^?2 day^?1 from February to August. A regional extrapolation indicated that respiration of this carbon potentially accounts for about half (46%) of annual CO₂ emissions from surface waters in the central Amazon, or about 44% of gaseous carbon emissions, if methane flux is included.     

Variation with age in the photosynthetic carbon fixation pattern by leaves of Amaranthus paniculatus and Oryza sativa: Change in the primary carboxylation but no shift from C4 or C3 pathway

Abstract The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C₄ plant) and Oryza sativa L. (a C₃ plant) varied with age. Younger leaves of A. paniculatus incorporated ¹⁴CO₂ into malate and aspartate while senescent leaves fixed predominantly into phosphoglycerate (PGA) and sugar phosphates. Only developing leaves of O. sativa formed malate/aspartate whereas mature and senescent leaves produced PGA/sugar phosphates as the initial labelled products. Correspondingly the ratio of phosphoenolpyruvate/ribulose bisphosphate (RuBP) carboxylase activities was higher in younger leaves of A. paniculatus and developing leaves of O. sativa than in older leaves. However, pulse chase experiments revealed that the main donors of carbon to end products, irrespective of leaf stage, were C₄ acids and PGA in A. paniculatus and O. sativa respectively. The results suggest that although an apparent change from initial β-carboxylation to RuBP carboxylation occurs during leaf ontogeny in both the plants, the overall leaf photosynthesis remains C₄ or C₃. The high rate of ¹⁴CO₂ incorporation into PGA/sugar phosphates by senescent leaves of A. paniculatus is suggested to be partly due to the increased intercellular spaces in their mesophyll, allowing greater access of CO₂ directly to RuBP carboxylase in the bundle sheath.     

Beach erosion and nest site selection by the leatherback sea turtle Dermochelys coriacea (Testudines: Dermochelyidae) and implications for management practices at Playa Gandoca, Costa Rica

Leatherback sea turtles (Dermochelys coriacea) nest on dynamic, erosion-prone beaches. Erosive processes and resulting nest loss have long been presumed to be a hindrance to clutch survival. In order to better understand how leatherbacks cope with unstable nesting beaches, I investigated the role of beach erosion in leatherback nest site selection at Playa Gandoca, Costa Rica. I also examined the potential effect of nest relocation, a conservation strategy in place at Playa Gandoca to prevent nest loss to erosion, on the temperature of incubating clutches. I monitored changes in beach structure as a result of erosion at natural nest sites during the time the nest was laid, as well as in subsequent weeks. To investigate slope as a cue for nest site selection, I measured the slope of the beach where turtles ascended from the sea to nest, as well as the slopes at other random locations on the beach for comparison. I examined temperature differences between natural and relocated nest sites with thermocouples placed in the sand at depths typical of leatherback nests. Nests were distributed non-randomly in a clumped distribution along the length of the beach and laid at locations that were not undergoing erosion. The slope at nest sites was significantly different than at randomly chosen locations on the beach. The sand temperature at nest depths was significantly warmer at natural nest sites than at locations of relocated nests. The findings of this study suggest leatherbacks actively select nest sites that are not undergoing erosive processes, with slope potentially being used as a cue for site selection. The relocation of nests appears to be inadvertently cooling the nest environment. Due to the fact that leatherback clutches undergo temperature-dependent sex determination, the relocation of nests may be producing an unnatural male biasing of hatchlings. The results of this study suggest that the necessity of relocation practices, largely in place to protect nests from erosion, should be reevaluated to ensure the proper conservation of this critically endangered species.     

A common binding site for primary prostanoids in vascular smooth muscles: a definitive discrimination of the binding for thromboxane A2/prostaglandin H2 receptor agonist from its antagonist

Differences in binding characteristics between agonists and antagonists for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor were examined in rat cultured vascular smooth muscle cells (VSMC). Scatchard analysis indicated the existence of two binding sites for the TXA2/PGH2 agonist, whereas a single class of recognition sites for the receptor antagonists were observed with approximately the same maximum binding capacity (Bmax) as a high-affinity binding site of the agonist. Weak binding inhibition by approx. 100 nM of primary prostanoids (PGE1, PGF2 alpha and PGD2) was detected only with the TXA2/PGH2 agonist, and not with the antagonist. Primary prostanoids as well as TXA2/PGH2 agonists (U46619 and STA2) suppressed the [3H]PGF2 alpha and [3H]PGE1 binding with almost the same potency, whereas TXA2/PGH2 antagonists (S-145, SQ29,548 and ONO3708) did not. The Bmax value of the binding sites was roughly identical in PGF2 alpha, PGE1 and a low-affinity binding site of U46619. These results suggest the existence of two binding sites for TXA2/PGH2 in VSMC, i.e., a high-affinity binding site corresponding to that of the TXA2/PGH2 antagonists and a low-affinity binding site in common with primary prostanoids.     

Stable coordination of the inhibitory Ca2+ ion at the metal ion-dependent adhesion site in integrin CD11b/CD18 by an antibody-derived ligand aspartate: implications for integrin regulation and structure-based drug design

A central feature of integrin interaction with physiologic ligands is the monodentate binding of a ligand carboxylate to a Mg(2+) ion hexacoordinated at the metal ion-dependent adhesion site (MIDAS) in the integrin A domain. This interaction stabilizes the A domain in the high-affinity state, which is distinguished from the default low-affinity state by tertiary changes in the domain that culminate in cell adhesion. Small molecule ligand-mimetic integrin antagonists act as partial agonists, eliciting similar activating conformational changes in the A domain, which has contributed to paradoxical adhesion and increased patient mortality in large clinical trials. As with other ligand-mimetic integrin antagonists, the function-blocking mAb 107 binds MIDAS of integrin CD11b/CD18 A domain (CD11bA), but in contrast, it favors the inhibitory Ca(2+) ion over the Mg(2+) ion at MIDAS. We determined the crystal structures of the Fab fragment of mAb 107 complexed to the low- and high-affinity states of CD11bA. Favored binding of the Ca(2+) ion at MIDAS is caused by the unusual symmetric bidentate ligation of a Fab-derived ligand Asp to a heptacoordinated MIDAS Ca(2+) ion. Binding of the Fab fragment of mAb 107 to CD11bA did not trigger the activating tertiary changes in the domain or in the full-length integrin. These data show that the denticity of the ligand Asp/Glu can modify the divalent cation selectivity at MIDAS and hence integrin function. Stabilizing the Ca(2+) ion at MIDAS by bidentate ligation to a ligand Asp/Glu may provide one approach for designing pure integrin antagonists.     

APPLIED ISSUES: Size‐dependent mortality of migratory silver eels at a hydropower plant,and implications for escapement to the sea

1. The European eel population has decreased drastically during recent decades, and new EU‐legislation calls for measures to change this negative trend. This decline has been attributed to a number of factors, including habitat fragmentation by structural barriers that prevent eels moving between freshwater and the sea. The success of downstream migrating adult silver eels migrating past a hydroelectric plant (HEP) in Sweden was examined by radio‐telemetry, and the results were considered in a historical context by analysing catch data from the river for 1957–2006. 2. The choice of routes and passage success were quantified for three treatment groups and one control group of silver eels. The first treatment, the reservoir group (n = 50), was released into the reservoir upstream of the HEP, and these fish could proceed downstream by passing through the HEP (20 mm rack and turbines) or by entering the spill gates into the former channel, bypassing the HEP. The second treatment group (inside rack, n = 15) was released downstream of the 20‐mm rack and had to pass through the turbines to continue migration to the sea. The third treatment group consisted of dead radio‐tagged eels (n = 6) that were released into the turbines to study the extent of drifting by dead individuals. Finally, the control group (n = 50) was released downstream of the HEP to test for effects of confounding factors. 3. Most live individuals displayed migratory behaviour and continued to proceed downstream after release. Only 8% of the fish released in the reservoir or downstream of the HEP (control) did not migrate. The probability of reaching the next HEP, 24 km further downstream, was high for the control group (96%) and the reservoir‐released individuals that passed the HEP via the spill gates and the former channel (83%). Survival was low and size‐dependent for the individuals that passed the turbines (40%) and even lower for the individuals that had to pass through the rack and the turbines (26%). The overall passage success for eels released in the reservoir was 30%, including both routes. 4. Annual catch data from 1957 to 2006 showed that the number of eels in the River Ätran has decreased. Despite this decrease, escapement biomass has remained unchanged, because of the fact that the mean size of eels has doubled. Passage data from 2007 show that changes in size and abundance have resulted in a reduction of relative escapement to the sea to values that are 21–24% of what they were in 1957–66. However, this low level of escapement could potentially be rectified if appropriate measures facilitating HEP passage are successfully implemented, since the potential escapement biomass in the river, owing to the large size of the eels, has changed little since the 1950s.     

Regulation of photosynthesis: Analysis of a model for sensitivity of delayed luminescence oscillation and the CO<Subscript>2</Subscript> fixation rate to variation of the model parameters

The oscillation behavior of delayed luminescence was addressed using the earlier proposed mathematical model [Karavaev and Kukushkin, Biofizika 38, 958 (1993)]. The oscillation frequency and damping factor were calculated by Lyapunov analysis. In calculations, each of the model parameters was varied in a broad range. The results suggest that, besides the oscillation mode observed experimentally, there may be other oscillations that are more rapidly damped. Analysis of how variation in the model parameters affects the CO₂ fixation rate has shown that CO₂ assimilation differently depends on the light absorbed by photosystems I and II.     

Cadmium and copper uptake and accumulation by Sesbania rostrata seedling, a N-fixing annual plant: implications for the mechanism of heavy metal tolerance

Sesbania rostrata, an annual tropical legume, has been found to be tolerant to heavy metals, with an unknown mechanism. It is a promising candidate species for revegetation at mine tailings. In this study, sequential extractions with five buffers and strong acids were used to extract various chemical forms of cadmium and copper in S. rostrata, with or without Cd or Cu treatments, so that the mechanisms of tolerance and detoxification could be inferred. Both metals had low transition rates from roots to the aboveground of S. rostrata. The transition ratio of Cd (4.00%) was higher than that of Cu (1.46%). The proportion of NaCl extracted Cd (mostly in protein-binding forms) increased drastically in Cd treated plants from being undetectable in untreated plants. This suggests that Cd induced biochemical processes producing protein-like phytochelatins that served as a major mechanism for the high Cd tolerance of S. rostrata. The case for Cu was quite different, indicating that the mechanism for metal tolerance in S. rostrata is metal-specific. The proportion of water-insoluble Cu (e.g. oxalate and phosphate) in roots increased significantly with Cu treatment, which partially explains the tolerance of S. rostrata to Cu. However, how S. rostrata copes with the high biotic activity of inorganic salts of Cu, which increased in all parts of the plant under Cu stress, is a question for future studies. Sesbania rostrata is among the very few N-fixing plants tolerant to heavy metals. This study provides evidence for the detoxification mechanism of metals in Sesbania rostrata.     

Thermolysis of coenzymes B12 at physiological temperatures: activation parameters for cobalt-carbon bond homolysis and a quantitative analysis of the perturbation of the homolysis equilibrium by the ribonucleoside triphosphate reductase from Lactobacillus leichmannii

The kinetics of the thermolysis of 5'-deoxyadenosylcobalamin (AdoCbl, coenzyme B12) in aqueous solution, pH 7.5, have been studied in the temperature range 30-85 degrees C using AdoCbl tritiated at the adenine C2 position and the method of initial rates. Combined with a careful analysis of the distribution of adenine-containing products, the results permit the dissection of the competing rate constants for carbon-cobalt bond homolysis and heterolysis. After correction for the temperature-dependent occurrence of the much less reactive base-off species of AdoCbl, the activation parameters for homolysis of the base-on species were found to be delta H++homo,on = 33.8 +/- 0.2 kcal mol-1 and delta S++homo,on = 13.5 +/- 0.7 cal mol-1 K-1, values not significantly different from those determined by Hay and Finke (J. Am. Chem. Soc. 108 (1986) 4820), in the temperature range 85-115 degrees C. In contrast, the heterolysis of base-on AdoCbl was characterized by a much smaller enthalpy of activation (delta H++het,on = 18.5 +/- 0.2 kcal mol-1) and a negative entropy of activation (delta S++het,on = -34.0 +/- 0.7 cal mol-1 K-1) so that heterolysis, which is minor pathway at elevated temperatures, is the dominant pathway for AdoCbl decomposition at physiological temperatures. Using literature values for the rate constant for the reverse reaction, the equilibrium constant for AdoCbl homolysis at 37 degrees C was calculated to be 7.9 x 10(-18). Comparison with the equilibrium constant for this homolysis at the active site of the ribonucleoside triphosphate reductase from Lactobacillus leichmannii shows that the enzymes shifts the equilibrium constant towards homolysis products by a factor of 2.9 x 10(12) (17.7 kcal mol-1) by binding the thermolysis products with an equilibrium constant of 7.1 x 10(16) M-2, compared to the bonding constant for AdoCbl of 2.4 x 10(4) M-1.     

Development and validation of a gas chromatography/ion trap-mass spectrometry method for simultaneous quantification of cocaine and its metabolites benzoylecgonine and norcocaine: application to the study of cocaine metabolism in human primary cultured renal cells

Acute renal failure is a common finding in cocaine abusers. While cocaine metabolism may contribute to its nephrotoxic mechanisms, its pharmacokinetics in kidney cells is hitherto to be clarified. Primary cultures of human proximal tubular cells (HPTCs) provide a well-characterized in vitro model, phenotypically representative of HPTCs in vivo. Thus, the present work describes the first sensitive gas chromatography/ion trap-mass spectrometry (GC/IT-MS) method for measurement of cocaine and its metabolites benzoylecgonine (BE) and norcocaine (NCOC) using a primary culture of HPTCs as cellular matrix, following solid phase extraction (SPE) and derivatization with N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA). The application of this methodology also enables the identification of two other cocaine metabolites: ecgonine methyl ester (EME) and anhydroecgonine methyl ester (AEME). The validation of the method was performed through the evaluation of selectivity, linearity, precision and accuracy, limit of detection (LOD), and limit of quantification (LOQ). Its applicability was demonstrated through the quantification of cocaine, BE and NCOC in primary cultured HPTCs after incubation, at physiological conditions, with 1 mM cocaine for 72 h. The developed GC/IT-MS method was found to be linear (r2 > 0.99). The intra-day precision varied between 3.6% and 13.5% and the values of accuracy between 92.7% and 111.9%. The LOD values for cocaine, BE and NCOC were 0.97±0.09, 0.40±0.04 and 20.89±1.81 ng/mL, respectively, and 3.24±0.30, 1.34±0.14 and 69.62±6.05 ng/mL as LOQ values.