Growth of grana from "primary" thylakoids in Phaseolus vulgaris

The plastids of young dark-grown bean leaves, exposed to periodiclight are agranal, devoid of chlorophyll b and contain primarythylakoids and chlorophyll a. Transfer of these plants to continuousillumination results in synthesis of new chlorophyll a, chlorophyllb and grana. This study was done in order to study whether andhow the grana are formed from preexisting primary thylakoids.¹⁴C--aminolevulinic acid was used to label the chlorophyll aof the primary thylakoids, and its fate was studied after transferof the plants to continuous light. It was found that chlorophyll b and grana become ¹⁴C-labelled.The total radioactivity of chlorophyll b per bean increasedwith the parallel decrease of that of chlorophyll a. All subchloroplastfractions, obtained after digitonin disruption of chloroplasts,contained chlorophyll a of equal specific radioactivity. Thespecific radioactivity of chlorophyll b was lower than thatof chlorophyll a, and, in addition, it was lower in the granathan in the stroma lamellae fraction. The data suggest that chlorophyll b is formed from chlorophylla; the grana are formed by stacking of preexisting primary thylakoids;chlorophyll b is synthesized faster in the grana than the stromalamellae; the newly formed chlorophyll a molecules are distributedat random throughout the developing photosynthetic membraneand not on specific growing sites. (Received April 24, 1976; )     

Diel variations in gut pigment content, diel vertical migration and estimates of grazing impact for copepods in the southern Benguela upwelling region in October 1987

The gut fluorescence technique was used to estimate ingestionand filtration rates of the adult female copepods Paracalanusparvus, Cenlropages brachiatus and Calanus austrails, and copepoditestages 3, 4 and 5 of C.australis in the southern Benguela upwellingregion. During the study period chlorophyll concentrations withinthe upper 20 m of the water column were high, 5 µg I^–1in mid-shelf waters and 15–30 µg I^–1 in innershelf waters. Copepod gut pigment content was low and constantduring the day then increased sharply during the first 2 h aftersunset. Gut pigment content was 2–6 times higher duringthe night compared with daytime values. Small non-migratingcopepods (Paracalanus parvus) showed the smallest diel differencein gut pigment content and large migrating copepods (Centropagesbrachiatus and Calanus australis) the largest difference. Eggproduction rates were 20 and 50% of maximum at the mid-shelfand inner shelf stations respectively, suggesting food-limitation.Comparison of ingestion rates calculated from egg productiondata with ingestion rates calculated from gut pigment data suggestedthat the copepods were feeding omnivorously at the inner shelfstations but herbivorously at the mid-shelf stations. Assumingthat all of the phytoplankton was available as food, the nearshorecopepod assemblage grazed {small tilde}1% of the standing cropeach day, and the mid-shelf assemblage grazed 5% day^–1.Because of errors and uncertainties associated with the gutfluorescence technique, the feeding impact could be underestimatedby 2–4-fold. We discuss several approaches which couldlead to more precise estimates of feeding rates. ³Present address: Marine Sciences, SUNY, Stony Brook, NY, 11794-5000,USA     

The Influence of Stress Conditions on Chlorophyll Content of Two Range Grasses with Contrasting Photosynthetic Pathways

The influence of various treatments and temperature regimeson total chlorophylls and on the chlorophyll a:b ratio of westernwheatgrass and blue grama plants was investigated at differenttime intervals during the 120-day growth period. Western wheatgrass,a C₃ species, accumulated greater amounts of chlorophyll thandid blue grama plants, a C₄ species. Maximum concentrations(mg gd wt^–1) of chlorophylls in western wheatgrass andin blue grama were recorded at the lower (13/7°C) and higher(30/18°C) temperature regimes. Nitrogen fertilizer alonedecreased the chlorophyll content in both species. The chlorophylla:b ratio in blue grama ranged from an average of 2·00under irrigated plus fertilized conditions to 3·00 undercontrol and fertilized conditions. On the other hand, the chlorophylla:b ratio in western wheatgrass remained constant at 3·00throughout the growing season under various treatments and temperatureregimes.     

Phytoplankton and zooplankton development in a lowland, temperate river

The longitudinal and seasonal patterns of plankton developmentwere examined over 2 years in a lowland, temperate river: theRideau River (Ontario, Canada). Following an initial decreasein phytoplankton and zooplankton biomass as water flowed fromthe headwaters into the Rideau River proper, there was an increasein chlorophyll a (chl a) and zooplankton biomass with downstreamtravel. At approximately river km 60, both phytoplankton andzooplankton reached their maximum biomass of 27 µg l^–1(chl a) and 470 µg l^–1 (dry mass), respectively.Downstream of river km 60, the biomass of both planktonic communitiesdeclined significantly despite increasing nutrient concentrationsand favorable light conditions. These downstream declines maybe due to the feeding activity of the exotic zebra mussel (Dreissenapolymorpha) which was at high density in downstream reaches(>1000 individuals m^–2). There was no evidence forlongitudinal phasing of phytoplankton and zooplankton, as increasesand decreases in chl a and zooplankton biomass appeared to coincide.Overall, chl a was best predicted by total phosphorus (R²=0.43),whereas zooplankton biomass was best predicted by chl a (R²=0.20).There was no evidence for significant grazing effects of zooplanktonon phytoplankton biomass.     

Effect of Sodium Dodecyl Sulfate on Structure and Spectroscopic Characteristics of Water-Soluble Chlorophyll Protein Complex Isolated from Stems of Lepidium virginicum

The relationship between structure and spectroscopic characteristicsof the watersoluble chlorophyll protein complex isolated fromstems of Lepidium virginicum (CP663S) was studied. Additionof 0.08% SDS induced a red shift of the 663 nm absorption maximum.At the same time, under excitation at 435 nm, the maximum offluorescence emission shifted from 672 nm to 675 nm and thefluorescence yield increased. When CP663S was excited at 480nm, the 660 nm emission band of chlorophyll b became more prominent.Fluorescence lifetime of emission from chlorophyll a increasedon addition of SDS. The energy transfer from chlorophyll b tochlorophyll a was decreased by the SDS addition, as judged bythe fluorescence spectra and lifetime measurement. Symmetricalpositive and negative peaks of the circular dichroism (CD) spectrumaround 669 nm, which indicate the interaction between chlorophylla molecules at short distances, disappeared after addition ofSDS. These SDS-induced changes of spectroscopic characteristicsoccurred in similar SDS concentration ranges and were reversible.SDS polyacrylamide gel electrophoresis cleaved CP663S into subunits.Chlorophyll molecules moved with protein moieties. Glutaraldehydetreatment suppressed the effects of SDS on absorption, fluorescenceand CD characteristics. We conclude that chlorophyll moleculesin CP663S are in the hydrophobic region of the protein and theinteraction between chlorophyll a molecules occurs at shortdistances. Changes of spectroscopic characteristics are a resultof cleavage of CP663S. ¹Present address: National Institute for Basic Biology, Okazaki444, Japan. (Received November 22, 1982; Accepted May 31, 1983)     

Are Mistletoes Shade Plants? CO2Assimilation and Chlorophyll Fluorescence of Temperate Mistletoes and their Hosts

Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO₂assimilation, chlorophyllfluorescence and the chlorophyll content of temperate host–parasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO₂assimilation (3.59 ±0.41 µmol m^-2 s^-1) than I. micranthus(2.42 ± 0.20µmol m^-2 s^-1), and C. serratus(2.41 ± 0.43 µmolm^-2 s^-1) showed higher CO₂assimilation than T. antarctica(0.67± 0.64 µmol m^-2 s^-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO₂assimilationand electron transport suggests that the lower CO₂assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO₂assimilation (3.21 ±0.37 µmol m^-2 s^-1) than mistletoes (2.54 ± 0.41µmol m^-2 s^-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO₂assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (q_p), non-photochemical quenching (q_n), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand     

Phytoplankton pigments at the Weddell-Scotia confluence during the 1993 austral spring

During a 1993 austral spring cruise, a complex biomass was encounterednear South Orkney Island that ranged from a low-biomass, Chaetocerostortissimus assemblage south of the front towards the ice edge,to a high-biomass, Thalassiosira gravida-dominated assemblageat the northern edge. The maximum levels of chlorophyll (Chl)a (up to 6 mg m^–3) were higher than those observed inprevious high-performance liquid chromatography-based studiesof pigments in the pelagic Southern Ocean. The non-photosyntheticpigment chlorophyllide a comprised up to 75% of the chlorophyllouspigments in the southern assemblage, but < 5% in the northernassemblage. Concentrations of the xanthophylls diadinoxanthin(DD) and diatoxanthin (DT), used as indicators of mean irradiance,indicated low-light-adapted populations. Low-light DD + DT/Chla ratios in surface waters indicated that vertical mixing limitedphytoplankton residence time in the near-surface layer, andthus limited exposure to maximum irradiance. Deck incubationsof natural assemblages indicated that the dark epoxidation reaction(i.e. the return of DT to DD) was a two-step reaction with theinitial rate being more rapid (t^1/2 = 9.5 min) than the second(t^1/2 = 55 min). Fucoxanthin, a major diatom pigment, was morestable chemically in the water column than Chl a, and the verticalprofiles of fucoxanthin followed those of chlorophyllide a insome cases. The formation and apparent stability of chlorophyllidea and fucoxanthin are important considerations when estimatingphotosynthetically active biomass over large regions of theocean.     

Seasonal variability of phytoplankton populations in the middle Adriatic sub-basin

The seasonal variability of phytoplankton assemblages in themiddle Adriatic sub-basin is described. The investigated areacrossed the middle Adriatic from the Italian to the Croatiancoasts. Hydrographic data, chlorophyll (Chl) a and phytoplanktonwere collected on a seasonal basis from May 1995 to February1996. Highest phytoplankton densities (up to 6 x 10⁶ cells dm^–3)were observed in spring and autumn in the western side, withinthe diluted waters. The vertical distribution of Chl a exhibiteda pronounced subsurface maximum associated, in coastal waters,with micro-planktonic diatoms. Phytoplankton assemblages weredominated by phytoflagellates in all the periods investigated.Diatom maxima were observed in spring and autumn: their verticaldistribution generally reflected the Chl a pattern and in thewestern coastal area peaks are due to large diatom species (Pseudo-nitzschiaspp.). In offshore waters, dinoflagellates strongly prevailover diatoms and provide a relevant contribution to the totalbiomass, especially in highly stratified conditions. Coccolithophoridswere mostly encountered in surface layers and their highestcontribution to the total biomass was observed in the LevantineIntermediate Water.     

Notes on a Mesodinium rubrum red tide in San Francisco Bay (California, USA)

Discrete red patches of water were observed in South San FranciscoBay (USA) on 30 April 1993, and examination of live samplesshowed that this red tide was caused by surface accumulationsof the pigmented ciliate Mesodinium rubrum. Vertical profilesshowed strong salinity and temperature stratification in theupper 5 m, peak chlorophyll fluorescence in the upper meter,and differences in the small-scale density structure and fluorescencedistribution among red patches. Events preceding this Mesodiniumred tide included: (i) heavy precipitation and run-off, allowingfor strong salinity stratification; (ii) a spring diatom bloomwhere the chlorophyll a concentration reached 50 mg m^–3;(ii) depletions of dissolved inorganic N and Si in the photiczone; and (iv) several days of rapid warming and stabilizationof the upper surface layer. These conditions may be generalprerequisites for M.rubrum blooms in temperate estuaries. ¹Present address: Station Marine d'Endoume, Centre d'Oceanologiede Marseille, rue Batterie des Lions, 13007 Marseille, France     

The optical properties of a turbid reservoir and its phytoplankton in relation to photosynthesis and growth (Mount Bold Reservoir, South Australia)

In situ light measurements were used to obtain information oninherent and apparent optical properties. The average verticalattenuation coefficient K_d(ave) varied from 1.1 to 4.6 In unitsm^–1 During three periods the variation in K_d(ave) correlatedwith changes in chlorophyll a concentration and specific attenuationcoefficients K_s, of 0.013, 0.014 and 0.022 m² mg Chl a^–1were calculated. Chlorophyll-specific diffuse absorption coefficients(A,) for these periods were 0.012. 0.013 and 0.017 m² mg Chla^–1 and only varied significantly from estimates of K_sin the period when scattering was intense. Absorption coefficientsa(z^mid) and scattering coefficients b(z^mid) calculated for themid-point of the euphotic zone ranged between 0.45 and 2.9 mand 3.5–52.0 m respectively. Chlorophyll-specific absorptioncoefficients K_a, of 0.005, 0.006 and 0.007 m² mg Chl a^–1and scattering coefficients K_b of 0.05. 0.09 and 0.191 m² mgChl a^–1 were measured during the three periods. The highK_b value occurred when gas-vacuolate cyanobactena were dominant.Algal photosynthesis and light absorption were related throughthe maximum quantum yield _m which varied between 0.019 and 0.11mol C Einstein^–1 while average quantum yields _a, variedbetween 0.006 and 0.024 with a mean of 0.013 mol C Einstein^–1A comparison of changes in the mean irradiance of the mixedzone and chlorophyll concentration indicated that growth waslight limited below 0.04–0.05 Einsteins absorbed mg Chla^–1 day^–1.     

The influence of water circulation on chlorophyll-turbidity relationships in Lake Okeechobee as determined by remote sensing

The spatial distribution of phytoplankton can be difficult toassess in shallow, productive aquatic systems due to frequentalgal blooms, high turbidity and sediment-resuspension events.We conducted a study to assess the distribution of suspendedparticles in Lake Okeechobee, Florida, utilizing both Landsat(1974–75) or Advanced Very High Resolution Radiometer(AVHRR) (1987) satellite remote sensing. Surface water sampleswere collected by helicopter to determine in situ chlorophyll-aand turbidity levels at 20 stations on four dates in 1974–75and six dates in 1987. Remotely sensed reflectance values agreedwell with in situ particle densities at the 20 in-lake stations(average R²: Landsat = 0.81, AVHRR = 0.53) and independent,synoptic boat mapping of algal blooms (r² = 0.79, P < 0.01).Basin-wide maps of chlorophyll and turbidity, as well as additionalspatial sampling, both indicated that these parameters are notnecessarily coupled in Lake. Our data concur with the hypothesisthat the spatial distributions of chlorophyll and turbidityare shaped by different forces. The highest concentrations ofchlorophyll occurred in the vicinity of tributary nutrient inputsat the lake's perimeter, while turbidity increased towards thecenter of the lake, reflecting predominant water circulationpatterns. ²Present address: Department of Biology & Romberg TiburonEnvironmental Center, San Francisco State University, San Francisco,CA 94132, USA ³Present address: Idaho Division of Environmental Quality, 1420North Hilton, Boise, ID 83706-1260, USA ⁴Present address: 5642 Santiago Circle, Boca Raton, FL 33433,USA     

Separation and Partial Characterization of Membranes from Prochloron sp.

Two differently colored membrane preparations were separatedfrom the prochlorophyte, Prochloron sp., by mechanical disintegrationof the cells followed by sucrose density gradient centrifugation.An orange-colored preparation, containing zeaxanthin as themajor constituent pigment, seemed to comprise the cytoplasmicmembrane. The other green-colored membrane preparation, containingß-carotene and chlorophyll a and b as major pigmentconstituents, was identified as the thylakoid membrane. Thetwo types of membranes were compared as to their absorptionspectra and buoyant densities. ¹ This work is one of the results of the 8th International Expeditionon Prochloron organized by Dr. R. A. Lewin, University of Californiaat San Diego. ⁵ Present address: Solar Energy Research Group, The Algatron,The Institute of Physical and Chemical Research (RIKEN), Wako-shi,Saitama 351, Japan. ⁶ Present address: National Institute for Basic Biology, Okazaki444, Japan. (Received October 19, 1984; Accepted January 7, 1985)     

CHLOROPHYLL FORMATION IN ISOLATED PUMPKIN COTYLEDONS IN THE PRESENCE OF KINETIN AND CHLORAMPHENICOL

Investigations have been made on the changes in the levels ofprotochlorophyll, chlorophyll a and chlorophyll b in relationto the kinetin induced expansion of isolated pumpkin cotyledonsin the presence and absence of chloramphenicol. It has been shown that rise in pigment level keeps pace withexpansion growth of the cotyledons. Kinetin markedly promotes the synthesis of protochlorphyll withoutmuch affecting the rate of its photoreduction to chlorophyll. Chloramphenicol strongly inhibits the development of both chlorophylla and b. The inhibition seems to be due to its interferenceboth with the synthesis of protochlorophyll and its subsequentconversion to chlorophyll. The inhibitory effect of chloramphenicol on the formation ofchlorophyll a is greater than on that of chlorophyll b, suggestingthereby the probability of divergent pathways for the formationof the two chlorophylls. (Received December 21, 1966; )     

Photoconversion of a Water-Soluble Chlorophyll Protein from Chenopodium Album: Resonance Raman and Fourier Transform Infrared Study of Protein and Pigment Structures

A water-soluble Chl a/b-protein complex, CP668, from Chenopodiumalbum converts to another form of protein complex, CP743, uponlight illumination. Structural changes of pigments and proteinsupon photoconversion were studied using resonance Raman (RR)and Fourier transform infrared (FTIR) spectroscopies. RR spectraof CP668 and CP743 and a light-induced FTIR difference spectrumshowed that the macrocyle C=C bands of Chl a in CP668 considerablychanged upon conversion to the pigment (not chemically identifiedyet) in CP743. The C=C band pattern of the RR spectrum of CP743was similar to that of bacteriochlorophyll a, suggesting thatthe conjugated system of the CP743 pigment resembles a bacteriochlorinring. Judging from the C=O frequencies, the 13¹-keto C=O groupsof Chl a and b in CP668 are free from hydrogen bonding, whereasthe 13²-ester C=O groups of both Chl a and b and the 7-formylC=O of Chl b in CP668 are hydrogen bonded. Upon conversion toCP743, interactions of the 13¹-keto and 13²-ester C=O groupswere basically unaffected, demonstrating no drastic changesaround these C=O groups. FTIR spectra in the amide I' regionof CP668 and CP743 in D₂O buffer showed a peak at 1,633 cm^–1,which represents a major component of ß-sheet conformation.Second-derivative spectra of the amide I' bands as well as alight-induced FTIR difference spectrum suggested that drasticchange in the protein conformation does not occur upon photoconversion. (Received November 1, 1998; Accepted December 24, 1998)     

Some properties of the chlorophyll fluorescence of the diatom Phaeodactylum tricornutum

Fluorescence transients were investigated with the diatom Phaeodactylumtricornutum. Supplementary experiments were done with Chaetocerossp. Under weak excitation ({small tilde}10³ erg/cm²sec), fluorescencetransients were induced simply by die oxidation-reduction reactionof Q, the primary reductant of photosystem II. The action spectraindicated that the electron transfer components between thetwo photosystems were in the most reduced state when fucoxanthinwas excited. The transients were observed with the 681 run emissionand with the 707 nm emission at room temperature. At –196°C,induction due to the reduction of Q. appeared both at the 681and 707 nm emissions. Similar results were also obtained withChaetoceros sp. Under strong excitation (10⁴–10⁵ erg/cm²-sec), the fluorescencetransients due to the interconversion between States 1 and 2of die pigment system (cf. ref. 27, 29) were observed. The transientswere induced by die alternate excitation of chlorophyll a andfucoxanthin or chlorophyll c. Conversion from State 2 to State1 was inhibited by DNP and CCCP, indicating that die processwas energy-dependent. Fluorescence spectra at –196°Cwere not altered by die state-conversion of die pigment system. These results suggest diat all die fluorescence bands whichappeared at room temperature and at –196°C were dueto die chlorophyll a of pigment system II in Phaeodactylum andChaetoceros. (Received September 7, 1972; )     

Seasonal reproductive biology of Centropages tenuiremis (copepoda) in Xiamen waters, People's Republic of China

The egg production rate (EPR) and the effects of environmentalvariations on diapause induction in the copepod Centropagestenuiremis in Xiamen waters were studied in 2002 and 2003. TheEPR ranged from 7.33 ± 8.14 (on 18 February 2003) to91.08 ± 20.61 (on 6 June 2003) eggs female^–1day^–1(mean ± 95% confidence limits), and displayed a significantseasonal pattern. Before the period of maximum egg production,EPR increased with seawater temperature and chlorophyll a concentration;but after the maximum, no significant relationship was foundbetween EPR and chlorophyll a concentration, and there was anegative linear relationship between EPR and temperature. Seawatertemperature and photoperiod, respectively, played a primaryrole in the switch to diapause egg production by the femalesas shown by single-factor probit analysis. However, the differencein effect between the two factors was demonstrated by binarylogistic multivariate analysis. These results suggest that thiscopepod rapidly increases subitaneous EPR by taking full advantageof conditions in favorable seasons (winter and spring). SubitaneousEPR decreases and there is a switch to the production of diapauseeggs that survive in the bottom sediments during unfavorableseasons (summer and autumn) in Xiamen waters.     

Changes in the Levels of Chlorophyll and Light-Harvesting Chlorophyll a/b Protein of PS II in Rice Leaves Aged under Different Irradiances from Full Expansion through Senescence

Effects of irradiance on changes in the amounts of chlorophyll(Chl) and light-harvesting chlorophyll a/b protein of PS II(LHCII) were examined in senescing leaves of rice (Oryza sativaL.). Results of treatments at two irradiances (100% and 20%natural sunlight) were examined after the full expansion ofthe 13th leaf throughout the course of senescence. With 20%sunlight, the Chl content decreased only a little during leafsenescence, while with 100% sunlight it decreased appreciably.Similarly, the amount of LHCII protein during treatment with20% sunlight remained almost constant. However, the ratio ofChl a/b during the shade treatment decreased significantly andthe rate of decrease was greater than during the full-sunlighttreatment. The ratio of Chl a/b for Chl a and b bound to LHCIIwas about 1.2, irrespective of leaf age or irradiance treatment.When the amounts of Chl bound to LHCII were calculated fromthe total leaf content of Chl and the ratio of Chl a/b, assuminga ratio of Chl a/b bound to LHCII of 1.2, they were well correlatedwith the amounts of LHCII protein. Changes in the amounts of LHCII synthesized during the two irradiancetreatments were examined using an ¹⁵ tracer. Incorporation of¹⁵N into LHCII declined dramatically during both treatmentsfrom full expansion through senescence, suggesting that therewas little synthesis of LHCII protein during that time. In addition,the amount of LHCII synthesized during senescence was lowerduring the shade treatment than during the 100% sunlight treatment.These results indicate that the absence of an apparent changein levels of LHCII with shade treatment during senescence wascaused by the very low rate of turnover of LHCII protein. (Received June 17, 1992; Accepted September 28, 1992)     

Can phaeopigments be used as markers for Daphnia grazing in Lake Constance?

The formation of chlorophyll a degradation products was measuredwith natural phytoplankton from Lake Constance and Daphnia magnaand native Daphnia as grazers in grazing experiments duringspring bloom conditions using high-pressure liquid chromatography(HPLC). Chlorophyll a start concentrations were between 1.2and 16.3 µg l^–1; phaeopigment weights constituted5% of chlorophyll a weight. Only phaeophorbide a was a markerfor Daphnia grazing; concentrations of other phaeopigments (phaeophytina, chlorophyllide a and two unidentified phaeopigments) didnot increase during Daphnia grazing. Conversion efficiencies(chlorophyll a to phaeophorbide a) were between 0 and 43% ona weight basis, and between 0 and 65% on a molar basis. Conversionefficiencies were highest at high grazer density (40 Daphnial^–1) and after a 24 h exposure time. Grazing by microzooplanktonprobably led to the formation of the two unidentified phaeopigments.In Lake Constance, Daphnia density was significantly positivelycorrelated with the phaeophorbide a/chlorophyll a ratio whenit was <5000 Daphnia m^–3. However, when higher Daphniadensities were included in calculations, then Daphnia densitywas positively, but insignificantly, correlated with the phaeophorbidea/chlorophyll a ratio. This suggests that when the level offood per Daphnia is low, then grazing is more efficient withless production of phaeophorbide a and a higher production ofcolourless products.     

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.     

Thylakoid Membrane Development and Differentiation: Assembly of the Chlorophyll a-b Light-Harvesting Complex and Evidence for the Origin of Mr=19, 17.5 and 13.4 kDa Proteins

Pea plants were grown under intermittent illumination (ImL)conditions. The low dosage of light given to ImL plastids limitedthe rate of chlorophyll (Chl) a and Chl b biosynthesis and,therefore, it retarded the rate of photosynthetic unit formationand thylakoid membrane development. Depending on the developmentalstage of the photosynthetic unit, ImL plastids had variableChl a/Chl b ratios (2.7 <Chl a/Chlb<20) and showed distinctintermediates in the assembly of the chlorophyll a–b light-harvestingcomplex (LHC) of photosystem-II (PSII). The results are consistentwith a step-wise increment in the PSII antenna size involvingthree distinct forms of the PSII unit: (i) a PSII-core formwith about 37 Chl a molecules; (ii) a PSIL_ß form containingthe PSII-core and the LHC-II-inner antenna with a total of about130 Chl (a + b) molecules, and (iii) the mature PSII_a form containingPSII_ß and the LHC-II-peripheral antenna with a totalof 210–300 Chl (a + b) molecules. The thylakoid membranecontained polypeptide subunits b, c and d (the Lhcb1, 2 and3 gene products, respectively) when only the LHC-II-inner waspresent. Polypeptide subunit a, (the apoprotein of the chlorophyll-proteinknown as CP29), along with increased amounts of b and c appearedlater in the development of thylakoids, concomitant with theassembly of the LHC-II-peripheral. The results suggest thatpolypeptide subunit d has priority of assembly over subunita. It is implied that, of all LHC-II constituent proteins, subunitd is most proximal to the PSII-core complex and that it servesas a linker in the transfer of excitation energy from the bulkLHC-II (subunits b and c) to the PSII-core. The work also addressesthe origin of low-molecular-weight proteins (M_r = 19, 17.5 and13.4 kDa) which co-isolate with intact developing plastids andwhose abundance decreases during plastid development. Aminoacid compositional and immunoblot analyses show a nuclear histoneorigin for these low-molecular-weight proteins and suggest co-isolationof histone-containing nuclear vesicles along with intact developingplastids. ¹Present address: Plant Physiology Research Group, The Universityof Calgary, Department of Biological Sciences, 2500 UniversityDrive N.W., Calgary, Alberta CANADA T2N 1N4.