Phagotrophy and NH4+ regeneration in a three-member microbial food loop

In a series of batch experiments we compared the efficiencyof nitrogen regeneration of a two- and three-member microbialfood loop consisting of a mixed bacterial assemblage, a small(3–5 µm) heterotrophic flagellate (Paraphysomonassp.), and a large (7–12 µm) heterotrophic flagellate(Paraphysomonas imperforata). In the two-member system the nitrogenregeneration efficiency for NH₄⁺ (R_n) was 41% and the grossgrowth efficiency (GGE) was 57% during active grazing by thesmall flagellate on bacteria. Regeneration of NH₄⁺ continuedduring the stationary phase so that R_n was 75% after 6 daysincubation. When the larger flagellate was introduced at theend of exponential growth of the smaller grazer in the three-membersystem, initially there was rapid regrowth of bacteria, tyingup 15% of the nitrogen originally in the bacteria. The largerflagellate grazed the smaller one with a GGE of 55%. Total nitrogenregeneration efficiency through exponential growth of the largerflagellate was 73%. Because microbial food loops in naturalwaters are far more complicated and with more grazing stepsthan portrayed in this study, we would expect the bulk of nutrientswithin these systems to be recycled with little transfer tohigher trophic levels.     

Modulation of hepatocellular swelling-activated K+ currents by phosphoinositide pathway-dependent protein kinase C

K⁺ channels participate in the regulatory volume decrease (RVD) accompanying hepatocellular nutrient uptake and bile formation. We recently identified KCNQ1 as a molecular candidate for a significant fraction of the hepatocellular swelling-activated K⁺ current (I_KVol). We have shown that the KCNQ1 inhibitor chromanol 293B significantly inhibited RVD-associated K⁺ flux in isolated perfused rat liver and used patch-clamp techniques to define the signaling pathway linking swelling to I_KVol activation. Patch-electrode dialysis of hepatocytes with solutions that maintain or increase phosphatidylinositol 4,5-bisphosphate (PIP₂) increased I_KVol, whereas conditions that decrease cellular PIP₂ decreased I_KVol. GTP and AlF₄^– stimulated I_KVol development, suggesting a role for G proteins and phospholipase C (PLC). Supporting this, the PLC blocker U-73122 decreased I_KVol and inhibited the stimulatory response to PIP₂ or GTP. Protein kinase C (PKC) is involved, because K⁺ current was enhanced by 1-oleoyl-2-acetyl-sn-glycerol and inhibited after chronic PKC stimulation with phorbol 12-myristate 13-acetate (PMA) or the PKC inhibitor GF 109203X. Both I_KVol and the accompanying membrane capacitance increase were blocked by cytochalasin D or GF 109203X. Acute PMA did not eliminate the cytochalasin D inhibition, suggesting that PKC-mediated I_KVol activation involves the cytoskeleton. Under isotonic conditions, a slowly developing K⁺ current similar to I_KVol was activated by PIP₂, lipid phosphatase inhibitors to counter PIP₂ depletion, a PLC-coupled ₁-adrenoceptor agonist, or PKC activators and was depressed by PKC inhibition, suggesting that hypotonicity is one of a set of stimuli that can activate I_KVol through a PIP₂/PKC-dependent pathway. The results indicate that PIP₂ indirectly activates hepatocellular KCNQ1-like channels via cytoskeletal rearrangement involving PKC activation. KCNQ1; patch clamp; phosphatidylinositol 4,5-bisphosphate; regulatory volume decrease     

Contrasting effects of substrate and grazer manipulations on picoplankton in oceanic and coastal waters off Brazil

In two contrasting regions off the coast of Brazil, picoplankton(<1 µm) responses to removal of larger grazers andto the additions of glucose and amino acids were determined.Effects of glucose and amino acid additions (1 µM) onparticulate nitrogen and chlorophyll a concentrations, and onrates of NH₄⁺ uptake and regeneration, were observed after 5h pre-incubation. In the oceanic waters, removal of the >1µm fraction had no significant effect on the chlorophylla of the picoplankton after 5 h. However, the addition of glucosestimulated both uptake and regeneration by a mean of 27%, andthe addition of arginine led to significant decreases in therates of NH₄⁺ uptake and regeneration. In contrast, in the coastalwaters, significant increases in chlorophyll and particulatenitrogen concentrations were found after 5 h incubation in boththe amended samples and in the controls, and mean rates of NH₄⁺uptake and regeneration were affected to a lesser degree bythe additions of either glucose or amino acids than in the oceanicwaters. The oceanic responses were suggestive of carbon limitationof heterotrophic bacteria. In the coastal region, on the otherhand, the supply of organic carbon and nitrogen was likely tohave been sufficient to meet the nutritional requirements ofthe heterotrophic bacteria and cyanobacteria. Grazing by largerorganisms on the picoplankton appeared to play a more significantrole in the nitrogen cycle in the coastal waters than in theoceanic waters.     

Estimation of ammonium regeneration efficiencies associated with bacterivory in pelagic food webs via a 15N tracer method

Phagotrophic protists are major components of pelagic food webs,both as consumers of bacterial and phytoplankton cells, andas regenerators of inorganic nutrients. In this study, we estimatedthe efficiency of ammonium regeneration by protists feedingon bacteria within natural plank-tonic assemblages, using a¹⁵N tracer method, in which the excretion of ¹⁵N-labeled ammoniumdue to grazing on ¹⁵N pre-labeled bacteria was followed overtime. We tested this approach in experiments based on the additionof heat-killed ¹⁵N-labeled bacteria to laboratory cultures andto samples of coastal seawater. During two experiments, variationin abundance of bacterivores and bacterioplankton resulted innon-constant grazing rates. Deterministic computer models thatused abundance of bacteria and protists as variables were developedto estimate best-fit values of grazing mortality (g, h^–1)and of ammonium regeneration efficiency (R_E, fraction of theinitial ¹⁵N label in added bacteria which is released as ammonium).Estimated ammonium R_E were 0.30–0.35 for one trophic linksystems with both a monospecific culture and a mixed speciesassemblage of bacterivorous flagellates. R_E was higher for multi-trophicstep food webs: 0.60 for 5 µm pre-screened coastal seawaterand 0.90 for whole coastal seawater.     

High Respiratory Activity of Guard Cell Protoplasts from Vicia faba L.

The rate of O₂ uptake was about 29 times higher in guard cellprotoplasts (GCPs) than in mesophyll protoplasts (MGPs) on aChi basis. The O₂ uptake was inhibited by respiratory inhibitors,but stimulated by respiratory uncouplers. On a Chi basis, theactivities of Cyt c oxidase and NADH-Cyt c reductase, mitochondrialenzymes, were about 27 and 35 times higher in GCPs than in MCPs.On a Chi basis, the ATP content was about 9 times higher inGCPs. The amount of ATP in GCPs was decreased by respiratoryinhibitors, an energy transfer inhibitor, and uncouplers ofoxidative phosphorylation. On a volume basis, GCPs had 8- to10-fold higher respiratory activities than MCPs, but had a lowChi content and lacked the activity of NADP-glyceraldehyde-3-phosphatedehydrogenase (NADP-GAPD), the Calvin cycle enzyme. From theseresults, we concluded that oxidative phosphorylation plays amain role in ATP production in guard cells and that guard cellshave a heterotrophic feature. Salicylhydroxamic acid (SHAM)in combination with KCN or NaN₃ strongly inhibited O₂ uptake,indicating the presence of cyanide-resistant respiration inguard cells. Phenylmercuric acetate (PMA), a potent inhibitorof stomatal opening, reduced the ATP content of GCPs by about90%, whereas it had a relatively small effect on the ATP levelof MCPs. The specific effect of PMA on GCPs is discussed. (Received March 24, 1983; Accepted June 8, 1983)     

Infection of sugar cane by the nitrogen-fixing bacterium Acetobacter diazotrophicus

Significant nitrogen fixation has recently been demonstratedin Brazilian sugar cane (Saccharum officinarum) cultivars knownto form associations with a number of diazotrophs, includingAcetobacter diazotrophicus, an acid-tolerant endophytic bacteriumwhich grows best on a sucrose-rich medium. In a series of experiments,aseptically-grown sugar cane plantlets were rooted in a liquidmedium and inoculated with A. diazotrophicus originally isolatedfrom field-grown sugar cane. After 4, 7, 9, and 15 d, plantswere examined under light, scanning and transmission electronmicroscopes and the presence of A. diazotrophicus on and withinplant tissues was confirmed by immunogold labelling. By 15 d,external bacterial colonization was seen on roots and lowerstems, particularly at cavities in lateral root junctions. Theloose cells of the root cap at root tips were a site of entryof the bacteria into root tissues. Both at lateral root junctionsand root tips, bacteria were also seen in enlarged, apparentlyintact, epidermal cells. After 15 d, bacteria were present inxylem vessels at the base of the stem, many connected via mucusto spiral secondary thickening. There was no obvious pathogenicreaction to the bacteria within the xylem. From these observations,it is proposed that, under experimental conditions, A. diazotrophicusfirstly colonized the root and lower stem epidermal surfacesand then used root tips and lateral root junctions to enterthe sugar cane plant where it was distributed around the plantin the transpiration stream. It is further suggested that thexylem vessels in the dense shoots of mature plants are alsoa possible site of N₂-fixation by diazotrophs as they providethe low pO₂ and energy as sucrose necessary for nitrogenaseactivity. Key words: Acetobacter diazotrophicus, endophyte, infection, nitrogen fixation, sugar cane.     

Inherent optical properties of the Irish Sea and their effect on satellite primary production algorithms

Three cruises were conducted in the Irish Sea during May, Juneand July 2001 to determine the variability in inherent opticalproperties (IOP), photo physiological parameters and primaryproduction (PP) and to assess the effect of IOP on satellitePP algorithms. The absorption coefficients of phytoplankton(a_ph), coloured dissolved organic material (a_CDOM) and nonalgalparticles (a_NAP) were higher during May than June and July.A radiative transfer model was used to model the in-water lightfield based on a_ph (case 1) and a_ph, a_CDOM and a_NAP (case 2).When PP was compared using these light fields, there was a 46%difference in estimates. The case 2 in-water light field wascoupled to a wavelength resolving satellite model of PP (PP_case2)and had a low root mean square error (RMS) (0.27 log₁₀PP) comparedwith in situ PP_case2. IOP absorption, especially a_CDOM, hada significant effect on the performance of this algorithm, butscattering of light by suspended particulate material had asmall effect. A look-up table was generated from the in situa_ph, a_CDOM and a_NAP measurements, which can be used in conjunctionwith satellite products to produce satellite maps of PP. Therewas <25% difference between in situ PP_case2 and the satellitePP maps, which suggests that they could be produced routinelyand accurately to monitor PP in the Irish Sea and other coastaland estuarine areas.     

Growth and grazing losses of prokaryotes in the central Atlantic Ocean

The trophic relation between prokaryotes and heterotrophic nanoflagellateswas studied during two latitudinal cruises in the central AtlanticOcean. The losses to predation on prokaryotes were determinedin 12 locations covering a wide range of trophic situations,from ultraoligotrophic [<0.05 mg chlorophyll a (Chl a) m^–3]to moderately eutrophic waters (>1 mg Chl a m^–3). Inthese locations, the abundance of prokaryotes (P) covaries withthat of heterotrophic nanoflagellates, thus suggesting thatresources controlled the abundance of heterotrophic nanoflagellates(HNF). Besides, the losses to predation were positively relatedto prokaryotic and heterotrophic nanoflagellate biomass, whichpoints toward higher consumption rates associated with largerconcentrations of preys and predators. Conversely, decliningtrends between prokaryotic production (P_P) and the fractionof this production lost to predation revealed higher relativelosses in the environments with lower productions. Our studyshows for the central Atlantic that 35% of prokaryotic biomass(B_P), equating to between 40 and 83% of P_P can be ingested dailyand that 55% of the variability observed in the rate of prokaryoticloss to predation was related with the HNF. As predators grazeon many prey types, in an oligotrophic system containing manyprey species but little numeric loading, there will still beprey for predators but not enough hosts for viruses. In thissense, our study confirms the importance of the prey–predatorrelationship between prokaryotes and heterotrophic nanoflagellatesin the flow of carbon of the less productive regions of theocean.     

A role for ERK1/2 in EGF- and ATP-dependent regulation of amiloride-sensitive sodium absorption

Receptor-mediated inhibition of amiloride-sensitive sodium absorption was observed in primary and immortalized murine renal collecting duct cell (mCT12) monolayers. The addition of epidermal growth factor (EGF) to the basolateral bathing solution of polarized monolayers reduced amiloride-sensitive short-circuit current (I_sc) by 15–25%, whereas the addition of ATP to the apical bathing solution decreased I_sc by 40–60%. Direct activation of PKC with phorbol 12-myristate 13-acetate (PMA) and mobilization of intracellular calcium with 2,5-di-tert-butyl-hydroquinone (DBHQ) reduced amiloride-sensitive I_sc in mCT12 monolayers by 46 ± 4% (n = 8) and 22 ± 2% (n = 8), respectively. Exposure of mCT12 cells to EGF, ATP, PMA, and DBHQ caused an increase in phosphorylation of p42/p44 (extracellular signal-regulated kinase; ERK1/2). Pretreatment of mCT12 monolayers with an ERK kinase inhibitor (PD-98059; 30 µM) prevented phosphorylation of p42/p44 and significantly reduced EGF, ATP, and PMA-induced inhibition of amiloride-sensitive I_sc. In contrast, pretreatment of monolayers with a PKC inhibitor (bisindolylmaleimide I; GF109203x; 1 µM) almost completely blocked the PMA-induced decrease in I_sc, but did not alter the EGF- or ATP-induced inhibition of I_sc. The DBHQ-mediated decrease in I_sc was due to inhibition of basolateral Na⁺-K⁺-ATPase, but EGF-, ATP-, and PMA-induced inhibition was most likely due to reduced apical sodium entry (epithelial Na⁺ channel activity). The results of these studies demonstrate that acute inhibition of amiloride-sensitive sodium transport by extracelluar ATP and EGF involves ERK1/2 activation and suggests a role for MAP kinase signaling as a negative regulator of electrogenic sodium absorption in epithelia. mitogen-activated protein kinase; epithelial ion transport; epithelial sodium channel     

The photoautotrophic culture of chlorophyllous cells

Photosynthesis in chlorophyllous cells in heterotrophic cultureswas investigated. Chlorophyllous cells from the amur cork-tree,scotch broom and tobacco, all of which had relatively high chlorophyllcontents (70 to 120 µg/g fresh weight) were selected throughoutcallus induction and cell subculture. When cultured under variouslight intensities, growth was stimulated by increases in lightintensity. This stimulation depended on the chlorophyll contentsof the cells. It disappeared on the addition of photosynthesisinhibitors (DCMU or 2-chloro-4,6-bis(ethylamino)-s-triazine).These phenomena indicate that photosynthesis accounted for athird to a half of cell growth under strong illumination. These heterotrophic cultures were then developed as autotrophiccultures. When these chlorophyllous cells were cultured withaeration using CO₂-enriched air in the light condition, thescotch broom and tobacco chlorophyllous cells grew photoautotrophically.Nearly the same amount of growth as with 3% sucrose in the darkwas observed in an autotrophic culture with aeration using aircontaining 1% CO₂. The green tobacco cells have been subculturedautotrophically for about one year. (Received November 28, 1977; )     

A comparative study on the effect of O2 on photosynthetic carbon metabolism by Chlorobium thiosulfatophilum and Chromatium vinosum

The reductive carboxylic acid cycle appears to be the majorcarbon assimilation pathway in green sulfur bacteria, Chlorobiumthiosulfatophilum. While cyanide was relatively ineffectivein inhibiting the bacterial photosynthetic CO₂ fixation, photosynthesiswas strongly impaired in an O₂-containing atmospheric environment.No glycolate formation was detected in Chlorobium under an O₂atmosphere. In the purple sulfur bacteria, Chromatium vinosum,however, photosynthesis was highly sensitive to cyanide, andin a short-term incubation (up to 10 min) photosynthetic CO₂fixation was found to be relatively indifferent to an O₂-containingatmosphere of up to 100% O₂. Significant formation of glycolatewas demonstrated upon a very brief exposure to O₂, whereas thetotal photosynthetic CO₂ fixation was slightly affected. However,ribulose-1,5-bisphosphate carboxylase activity in Chromatiumextract was competitively inhibited by O₂ in a similar mannerto the higher plant enzyme, K¹(O₂) value being 0.7 mM at pH8.2. The percentage of incorporation of ¹⁴CO₂ into glycolateand glycine under an O₂-containing atmosphere declined withincreasing levels of bicarbonate concentrations in the medium.The Warburg effect and biosynthetic mechanisms involving glycolatein photosynthetic bacteria are discussed. ¹ This is paper XXXIX in the series "Structure and Functionof Chloroplast Proteins". Paper XXXVIII is reference (6) Asamiand Akazawa (1977). This research was supported in part by grantsfrom the Ministry of Education of Japan (111912), the TorayScience Foundation (Tokyo), and the Japan Securities ScholarshipFoundation (Tokyo). (Received January 28, 1977; )     

Rates of microbial degradation of dissolved organic carbon from phytoplankton cultures

Dissolved organic carbon (DOC) decay was measured for samplesfrom cultures of the diatoms Chaetoceros gracilis and Phaeodactylumtricornutum, the flagellate Isochrysis galbana, the dinoflagellateAlexandrium tamarense, and a natural algal assemblage from theNorthwest Arm, Nova Scotia, Canada, by a high-temperature catalyticoxidation (HTCO) method. Decay rate constants were determinedusing first-order reaction kinetics in the multi-G model ofBerner (In Early Diagenesis, a Theoretical Approach, PrincetonUniversity Press, 1980). Decay rates as high as 0.37 day^–1wereobtained, which demonstrated that DOC released by phytoplanktonmight be highly labile to bacterial utilization and could bedegraded significantly within hours. Decay rates for most speciestested followed much the same pattern, with K₀₁ values around0.3–0.4, K₀₂ values around 0.03, and K₀₃ and K₀₄ valuesaround 10^–3 day^–1. DOC released by the senescentcells of A.tamarense was found to be essentially bacteria resistant,in contrast to that of the other species tested. The decay ofDOC was directly temperature dependent over the 10–20°Crange. Six methods for DOC preservation were tested. Acidificationwith HCl and refrigerated storage was demonstrated to be themost convenient and practical method. This method can be usedfor both short- and long-term preservation of DOC samples containinghighly labile organic compounds.     

PHOTOCHEMICAL INTERCONVERSION BETWEEN PRECURSORS OF PHYCOBILIN CHROMOPROTEIDS IN TOLYPOTHRIX TENUIS

1. The photochemical conversion between the precursors of phycocyaninand phycoerythrin in Tolypothrix tenuis was investigated.
2. Itwas found that the conversion of phycocyanin-precursor intophycoerythrin-precursor was induced by green light, and thereverse reaction by red light. These reactions proceeded exponentially, indicating that the photochemical process was acceleratedautocatalytically by the reaction-product.
3. The rates of thesephotochemical reactions were found to beunaltered by varyingthe incubation temperature (0? to 35?)and the composition ofthe gas atmosphere (presence or absenceof CO₂ and of O₂ orby an inhibitor of photosynthesis, p-chlorophenyldimethylurea.
4. The action spectra of the photochemical interconversions betweenprecursors of phycobilin chromoproteids were found to be distinctlydifferent from the absorption spectra of chlorophyll and carotenoids.The most effective wavelength for inducing the conversion ofphycocyanin- into phycoerythrin-precursor (541 mµ) isnear the absorption maximum of phycoerythrin (565 mµ),and that of the reverse reaction (641 mµ) is near theabsorption maximum of phycocyanin (620 mµ). Additionaldata, indicating that the phycobilin chromoproteids themselvesdo not participate in these processes as light absorber, werealso presented.
5. On the basis of these results, a possiblemechanism of the photochemicalinterconversion between the precursorsof phycobilin chromoproteidsis proposed.

(Received March 13, 1962; )     

Microbial decomposition of dissolved organic matter in a hypertrophic pond

Planktonic heterotrophic bacteria in lakes utilize the labile fraction of dissolved organic carbon (DOC), although information about seasonal changes in labile DOC in hypertrophic lakes in terms of absolute amount and relative proportion of the total DOC is still limited. We conducted DOC decomposition experiments using GF/F filtrates in water samples from hypertrophic Furuike Pond, together with monitoring of DOC concentration and bacterial abundance in water samples from the pond, to examine seasonal changes in the amount of labile DOC and growth of bacteria on labile DOC. DOC concentrations fluctuated between 2.7 and 11 mg C l⁻¹, and bacterial abundance fluctuated between 1.5 × 10⁶ and 1.0 × 10⁸ cells ml⁻¹. In the DOC decomposition experiment when grazers of bacteria were removed, small portions of DOC (18% ± 12%) were labile for decomposition by bacteria, and the growth yield of bacteria on labile DOC ranged between 3.3% and 19%. Furthermore, addition of nitrogen to water samples enhanced bacterial growth. Thus, not only labile DOC but also nitrogen limited bacterial growth in the pond. Considering the results in the present study together with those of previous studies, bacterial abundance in Furuike Pond is subjected to bottom-up control, such as by limitation of DOC and nitrogen throughout the year, although top-down control of bacterial abundance such as by grazing is seasonally important. Received: May 1, 2001 / Accepted: July 22, 2001     

Vitamins, phytoplankton and bacteria: symbiosis or scavenging?

The conclusion that over 25% of global primary production dependson direct algal/bacterial symbiosis involving vitamin B₁₂ [Croftet al., (2005) Algae acquire vitamin B₁₂ through a symbioticrelationship with bacteria. Nature, 438, 90–93] is patentlyfalse, for it is based on a misconception of the probable levelof the vitamin B₁₂ requirement in marine pelagic algae. A reviewof the various published attempts at measuring this requirementsuggests that it is likely to be so low that oceanic and coastalconcentrations of the vitamin would usually be sufficient tosustain the populations that occur without the assistance ofdirect algal/bacterial symbiosis. The levels measured are discussedin relation to method (batch or continuous culture) and protocolsused. Requirement values considered by the author to be acceptablerange from 0.1 to 0.3 pM for the vitamin growth saturation constant(K_S) and from 30 to 100 µL algal biomass pmol^–1vitamin for the yield.     

Isolation of the Photoactive Reaction Center Complex that Contains Three Types of Fe-S Centers and a Cytochrome c Subunit from the Green Sulfur Bacterium Chlorobium limicola f. thiosulfatophilum, Strain Larsen

The photoactive reaction center (RC) complex from the greensulfur bacterium Chlorobium limicola f. thiosulfatophilum, strainLarsen, was isolated after solubilization and ammonium sulfatefractionation followed by ion-exchange chromatography. The spectrumof the complex was almost identical with that of the similarRC complex isolated by Feiler et al. [(1992) Biochemistry 31:2608–2614] except for the presence of cytochrome c₅₅₁instead of c₅₅₃ in the latter study. A molecular ratio of BChla to P840 of the isolated RC complex was assayed to be 25–35.SDSPAGE analysis revealed that the isolated complex containedthree major polypeptides with apparent molecular masses of 68,41 and 21 kDa, respectively. The 21-kDa polypeptide was identifiedto be a heme-binding protein by staining the gel for peroxidaseactivity. The cytochrome c₅₅₁ was oxidized by flash light ina biphasic manner with half times of 90 and 390 µs, respectively,that coincided with the reduction half times of P840⁺. Threedistinct iron-sulfur centers assigned to F_A, F_B and F_x, respectively,from their g-values were detected by EPR spectroscopy at cryogenictemperature. These results suggest that the present preparationcontains a minimal functional unit of the RC of this bacterium,and that this complex appears to lie on a evolutionary linebetween RC's of purple bacteria and photosystem I. (Received August 18, 1992; Accepted October 28, 1992)     

Variability of the amplification factor of light absorption by filter-retained aquatic particles in the coastal environment

The amplification of light absorption by aquatic particles retainedon glass-fiber filters, the so-called ß factor, has beenmeasured for 29 stations located in the varying coastal environmentof the northern basin of the Adriatic Sea. The spectral valuesof the optical density of particles have been determined onglass-fiber filters by the standard transmittance (T) methodas well as by the transmittance-reflectance (T-R) method, whichperforms an accurate correction for light backscattering bythe particles, and on glass slides by the modified filter–transfer–freeze(FTF) method, which eliminates the pathlength amplification.It has been shown that the relationships between the opticaldensities of particles on glass slides (OD_sus) and on glass-fiberfilters (OD_f) have a low dispersion when OD_f is measured bythe T-R method: in this case, the use of a single expressionfor all stations adds an error that does not exceed the typicaluncertainty of the measurement of the filter-retained particleabsorption. On the contrary, the OD_sus versus OD_f plots obtainedby the T method exhibit considerable variability, apparentlydue to the approximate correction for light backscattering performedby this method, and do not permit the use of a single equationfor all stations.     

Carotenoid photobleaching induced by photosystem II action in the membrane fragments of the blue-green alga Anabaena variabilis : Action of O2

Carotenoid photobleaching induced by photosystem II action wasstudied using membrane fragments of the blue-green alga Anabaenavariabilis. Special attention was paid to the action of O₂. Carotenoid photobleaching elicited by carbonyl cyanide m-chlorophenylhydrazone(CCCP) depended on O₂. However, the addition of H₂O₂, sodiumsilicotungstate or potassium ferricyanide (Ferri), an electronacceptor for reaction center II action, removed the O₂-dependency.These results indicate that O₂ acts as the electron acceptorfor this reaction. When both CGCP and Ferri were present, a short illumination(0.25 sec) caused a rapid photobleaching followed by a slowrecovery in the subsequent dark period. The spectrum of theabsorption decrease in the light was identical with that ofthe absorption increase in the subsequent dark, indicating thata reversible process is involved in the carotenoid photobleaching.The size in the dark recovery relative to the light bleachingbecame larger under anaerobic conditions and smaller under higherpartial pressure of O₂. The reuslts were interpreted as indicatingthat O₂ does not function in the primary process including areversible bleaching step, but is involved in the slow and irreversiblebleaching process. (Received April 3, 1978; )     

Sample preconditioning for measurement of fluorescence induction of chlorophyll a in marine phytoplankton

Conditions for measuring fluorescence induction curves (time-scalems) of in vivo chlorophyll ^a were studied using cultures ofDunaliella tertiolecta Butcher (Chlorophyceae) and of Thalassiosirapseudonana Hustedt (3H) (Bacillariophyceae), and samples ofnatural phytoplankton populations from the Grand Banks. Thearea above the fluorescence induction curve (A_DCMU) and themaximum fluorescence intensity (F_max) measured in the presenceof 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) were computedby microcomputer. Cells must be ‘conditioned’ or‘adapted’ prior to obtaining a fluorescence inductioncurve; dark-adaptation resulted in a lower A_DCMU and F_max thandid adaptation in far-red (720 nm) light, and was the conditioningmethod chosen. A_DCMU and F_max increased linearly with increasingirradiance up to 32.8 W m^–2 the highest actinic irradianceavailable. Information on the light history of D. tertiolectawas obtained by following the time-course of change in A_DCMUand in F_max for cells exposed for 10 min to far-red or to bluelight. The rise-time of the fluorescence induction curve andvalues of F_max were greater for samples of D. tertiolecta concentratedonto glass-fiber filters than for liquid samples, however, valuesof A_DCMU for filtered and liquid samples were not significantlydifferent. Samples of Grand Banks phytoplankton collected ontoglass-fiber filters and frozen for 28 d exhibited a significantdecrease in F_max and in A_DCMU relative to the same freshly-filteredsamples. Filtration and freezing of samples is not recommended. ^*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.     

Biosynthetic mechanism of glycolate in Chromatium I. Glycolate pathway

The pattern of radioactivity distribution in several amino acidsof Chromatium cells exposed to ¹⁴CO₂ was determined. By transferringthe bacterial cells from an atmosphere of nitrogen to oxygenthere occurred a transient decrease of ¹⁴CO₂ incorporation intoaspartate and glutamate, whereas that into glycine showed aprominent increase. The labeling of both serine and alaninedid not show a marked change under such conditions. The, activitiesof glycolate oxidase and glycolate dehydrogenase in crude extractsof the bacterial cells were very low. The formation of glycolic acid only occurred during the oxidativemetabolism of Chromatium cells grown on bicarbonate as a C source,being negligibly small in bacteria under nitrogen or after growthon malate or acetate. The activities of both ribulose- 1,5-bisphosphateoxygenase and phosphoglycolate phosphatase in the extract preparedfrom the bicarbonate-grown bacterial cells were very low andapparently could not account for the glycolic acid formationthrough these enzymic reactions. Metabolic patterns of glycolicacid in Chromatium are discussed in relation to the photorespiratoryphenomenon. (Received February 24, 1975; )