Formation of protochlorophyll(ide) in wild type and mutant C-2A' cells of Scenedesmus obliquus

Protochlorophyll(ide) was isolated from dark-grown wild typeand mutant C-2A' cells of Scenedesmus obliquus after dark incubationwith 5-aminolevulinate. Proto-chlorophyll(ide) was detectedin mutant cells grown heterotrophically at 29°C or at 21°C.At the latter temperature chlorophyll synthesis was significant.Regulation of chlorophyll synthesis in algae is discussed. ¹Present address: Laboratory of Chemistry, Faculty of Medicine,Teikyo University, Otsuka, Hachioji, Tokyo 192-03, Japan. (Received July 14, 1980; )     

Low Temperature Treatments Induce an Increase in the Relative Content of Both Linolenic and {lambda}3-Hexadecenoic Acids in Thylakoid Membrane Phosphatidylglycerol of Squash Cotyledons

The effect of low temperatures on the fatty acid compositionof phosphatidylglycerol (PG) in thylakoid membranes, in particularon the ratios of nmol% 16:1(3t) (mg fresh weight)^–1 ofcotyledons and nmol 16:1(3t) (mg chlo rophyll)^–1 weremeasured during squash seedling growth. Plants were germinatedand grown for one day at 30°C then were either kept at 30°C(control plants) or trans ferred to low temperatures (18, 14or 10°C). When plant were transferred from 30°C to lowtemperatures, the increase in fresh weight was gradually limited.The lowe the temperature, the smaller was the fresh weight.In contrast, the relative content of 16:1(3t) and 18:3, as wella the ratios of nmol 16:1(3t) (mg chlorophyll)^–1 and mol%16:1(3t) (mg cotyledon fresh weight)^–1 increased indicatingthat the increase of fresh weight and chlorophyll was mor sensitiveto low temperature than PG desaturation in thyla-koid membranes.Furthermore, low temperatures inducei an increase in 16:1(3t)and 18:3 (the final products of PC synthesis) at the expenseof 16:0 and 18:1 (the initial products of PG synthesis). However,within a range of temperature from 10 to 18°C, the extentof these changes (nmol% of 18:3 or 16:1(3t) per day) was graduallylimited by lower temperatures. We therefore propose that lowtemperature inhibit both fatty acid synthesis and desaturationactivities. However, at low temperatures the fatty acid synthesisis likely to be more strongly inhibited than the desaturationactivities, thus explaining the observed increase in the relativecontent of PG-18:3 and PG-16:l(3t). Results an discussed interms of the mechanism which could be in volved in the metabolismof PG in squash cotyledons. (Received July 5, 1996; Accepted March 10, 1997)     

The Effects of Temperature on 86Rb Uptake by Two Species of Chlamydomonas (Chlorophyta, Chlorophyceae)

⁸⁶Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, ⁸⁶Rb uptake was abolished. Cells cooled rapidlyto –5°C in the absence of ice accumulated ⁸⁶Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and ⁸⁶Rb uptake, albeit slow, was measurable at–5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced ⁸⁶Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate ⁸⁶Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, ⁸⁶Rb uptake, membrane     

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; )     

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.     

Chlorophyll Deficiency Caused by a Specific Blockage of the C5-Pathway in Seedlings of Virescent Mutant Rice

Temperature-sensitive mutants of rice, designated virescent(v₁, v₂ and v₃), develop chlorophyll-deficient leaves at a restrictivetemperature (20°C) but develop nearly normal green leavesat a permissive temperature (30°C). Analysis of the chlorophyllbiosynthetic pathway in the virescent mutants indicated thatthe chlorophyll deficiency at the restrictive temperature wasdue to specific blockage of the C₅-pathway. Northern analysissuggested that the chlorophyll deficiency in the virescent mutantswas caused by specific inhibition of the expression of chloroplasttRNA^Glu. (Received October 22, 1993; Accepted January 25, 1994)     

RNA Synthesis in Phaseolus Chloroplasts: I. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLAST PREPARATIONS FROM PHASEOLUS VULGARIS L. LEAVES AND SOLUBILIZATION OF THE RNA POLYMERASE

Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg^–1 chlorophyll h^–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl₂. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl₂. The simultaneouspresence of MnCl₂ and MgCl₂ resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg^–1 DNA h^–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.     

Chlorophyll Synthesis from Protochlorophyll(ide) in Chill-Stressed Maize (Zea mays L.)

Illumination of aetiolated maize at temperatures lower than20 °C results in negligible accumulation of chlorophyll.Illumination of leaf tissue, previously incubated in 10 molm^–3 ALA in darkness, shows only a slight conversion ofprotochlorophyll(ide) to chlorophyll a and b at temperaturesless than 20 °C. A refined procedure for measuring photosynthesisby photo-acoustic spectroscopy in leaves that differ in chlorophyllcontent is presented. Studies of photosynthesis in aetiolatedseedlings illuminated at different temperatures by photo-acousticspectroscopy suggests that impairment of the chlorophyll pathwayis paralleled by an aberrant development of the thylakoid membrane. Key words: Protochlorophyll(ide), temperature, photo-acoustic spectroscopy, membrane biogenesis     

Heat Shock Proteins of Cyanobacterium Anacystis nidulans

Cells of Anacystis nidulans grown at 30°C were incubatedwith ¹⁴C-Chlorella protein hydrolysate at the elevated temperatures(30–55°C) and the effect of heat shock treatment onprotein synthesis was studied. Incubation temperatures higherthan 45°C caused a significant decrease in the incorporationof amino acids into proteins. Further, the heat shock treatmentinduced significant changes in the fluorographic profile ofthe newly synthesized proteins. (Received October 25, 1985; Accepted December 4, 1985)     

Studies on chloroplast development in Chlamydomonas reinhardtii I. Effect of brief illumination on chlorophyll synthesis

When dark grown cells of Chlamydomonas reinhardtii y-1 mutantwere exposed to continuous light, an immediate transformationof small amounts of protochlorophyll(ide), which had been presentin the dark grown cells, to chlorophyll was observed. Afterthis, there was a slow accumulation of chlorophyll lasting for2.5-3 hr before the start of exponential synthesis. Initialaccumulation of chlorophyll was distinctly slower at a highlight intensity (13,000 lux) than it was at moderate intensitiesof light (2,000–5,000 lux). However, the exponential synthesisof chlorophyll started after the same 2.5–3 hr of illumination. A brief pre-illumination of cells followed by incubation indarkness was effective in promoting chlorophyll synthesis undersubsequent continuous illumination at high, as well as moderatelight intensities. Pretreatment alleviated retardation of theinitial chlorophyll accumulation by light of high intensity.The promoting effect of preillumination on chlorophyll synthesiswas sufficient, even when a light impulse as short as 10 secwas given. However, the effect was dependent on length of thedark period after the short pre-illumination. The full extentof this effect was observed when the dark period was about 2.5–3hr long. Further dark incubation gradually decreased the effect. On the basis of these findings, it is assumed that a factor(s)responsible for promotion of chlorophyll (or chloroplast) synthesisin the process of greening of dark grown cells is produced duringthe dark period after a brief pre-illumination, and that thefactor is turned over at a relatively fast rate. The possiblenature of the presumed factor is discussed in relation to chloroplastdevelopment. ¹Present address: Department of Biology, Faculty of Science,Kobe University, Nada-ku, Kobe, Japan. (Received August 18, 1970; )     

Effect of temperature and food concentration on post-embryonic development, egg production and adult body size of calanoid copepod Eurytemora affinis

Post-embryonic development time, egg production rate and adultbody size of calanoid copepod Eurytemora affinis from Lake Ohnuma,Japan, were determined under six temperature-food conditions(10³,5 x 10³, 10⁴ and 5 x 10⁴ cells ml^–1 at 15°C,5 x 10⁴ cells ml^–1 at 10and20°C) in the laboratory.The measured parameters varied with both temperature and foodconcentration. Development time from hatching to adult femalewas 9.2, 11.4 and 22.8 days at 20, 15 and 10°C respectively,at the highest food concentration. The males developed to adultat one to two days earlier than the females. An effect of foodshortage on development time occurred at the lowest food concentration.This development time was 24.8 days even at 15°C, beingtwice as long as that at the highest food concentration. Prosomelength of these food-limited females was approximately 75% ofwell-fed ones, which reduced by only 10% with increasing temperaturefrom 10 to 20°C. Clutch size (C, eggs clutch^–1) ofwell-fed individuals depended on prosome length of the adultfemale (L, mm), and was expressed as an equation: C = 65.2 L³⁸³. Clutch size of individuals reared at less than 10⁴ cellsml^–1, however, mostly laid below the estimated curve,especially at the lowest food concentration being only 10% ofthat at the highest food concentration. These results suggestthat food availability is a more important factor affectingpopulation growth of E.affinis in Lake Ohnuma than variationof temperature.     

The relative importance of food and temperature to copepod egg production and somatic growth in the southern Benguela upwelling system

The fecundity and somatic growth rates of Calanus agulhensisand Calanoides carinatus, the dominant large calanoid copepodsin the southern Benguela upwelling system, as well as the fecundityof several other common copepods, were measured between Septemberand March of 1993/94 and 1994/95. Mean egg production of mostcopepods was low at >30 eggs female^-1 day^-1 {Calanoides carinatus23.7, Calanus agulhensis 19.0, Neocalanus tonsus 16.1 and Rhincalanusnasutus 26.1), whereas the mean fecundity of Centropages brachiatuswas significantly greater (83.6 eggs female^–1 day^-1).This study also presents the first comprehensive field estimatesof the fecundity of Nanno-calanus minor (mean: 26.1 eggs female^–1day^–1, range: 0.0–96.2 eggs female^–1 day^–1)and of somatic growth of N6 and all copepodite stages of Calanoidescarinatus (decreasing from 0.58 day^–1 for N6 to 0.04 day^–1for C5). Somatic growth rates of Calanus agulhensis also declinedwith age: from 0.57 day1 for N6 to 0.09 day1 for C5. Data ongrowth rates were used to assess the relative importance offood [as measured by total chlorophyll (Chi) a concentration],phytoplankton cell size (proportion of cells >10 µm)and temperature to the growth of copepods. Multiple regressionresults suggested that fecundity and somatic growth rates werepositively related to both Chi a concentration and phytoplanktoncell size, but not to temperature. Although it was not possibleto separate the effects of Chi a concentration and phytoplanktoncell size, data from previous laboratory experiments suggestthat copepod growth is not limited by small cells per se, butby the low Chi a concentrations that are associated with theseparticles in the field. Despite growth not being directly relatedto temperature, a dome-shaped relationship was evident in somespecies, with slower growth rates at cool (<13°C) andwarm (>18°C) temperatures. The shape of this relationshipmirrors that of Chi a versus temperature, where poor Chi a concentrationsare associated with cool and warm temperatures. It is concludedthat the effect of food limitation on growth of copepods outweighsthat of temperature in the southern Benguela region. Sourcesof variability in relationships between growth and Chi a concentrationare discussed.     

Effect of light regime upon growth rate and chemical composition of a clone of Skeletonema costatum from the Trondheimsfjord, Norway

Nutrient-saturated cultures of Skeletonema costatum were grownat 15C and 42 combinations of photon flux density (PFD) anddaylength. The growth rate increased with the daylength andPFD up to 460–630 µE m^–2 s^–1 (maximum2.5 doublings day At 2000 µE m^–2 s^–1 the growthrate was reduced by 45%. The chlorophyll (chl) content of thecells and the rate of production of carbon per unit chlorophylland ambient light increased for declining light regimes as didcellular nitrogen and carbon. The N/C ratio, cellular phosphorusand ratios between in vivo fluorescence, with and without DCMU,and chlorophyll varied negligibly. The ATP/C ratio was linearlyrelated to the growth rate. The results were described mathematically.The chl/C ratio was low both in strong light and in marginallylow light, corresponding to low cellular chlorophyll and highcellular carbon, respectively. The observed increase in cellularnitrogen and carbon at shade adaptation probably represent anincrease in the size of internal stores of organic nitrogenand may imply that Skeletonema cells become enriched with organicnitrogen when staying in nitrate-rich subsurface layers, e.g.in or below a nutricline. However, close to zero growth in marginallight the cells become greatly enriched with respect to everymeasured factor. Such cells may be physiologically resting stageswhich may ensure survival during dark periods and promote rapiddevelopment during the initial phase of blooms. Cultures andnatural blooms of Skeleronema in the Trondheimsfjord exhibitvery similar patterns of variation.     

The Effect of Ethylene and Temperature on ATP Accumulation from Various Substrates in Peanut (Arachis hypogaea L. ) Seeds

Peanut (Arachis hypogaea L. ) seed powder accumulated ATP fromAMP and phosphoenolpyruvate (PEP) at a rate of approx. 100 pmolmin^–1mg^– powder at 35° C. When peanut seed powderwas incubated with various substrates, which may result in PEPor AMP (ADP) synthesis, then ATP accumulated. The best substratecombinations examined so far were AMP + succinate, NADH₂, andAMP + malate + NAD, with activities of 33, 12 and 12 pmol min^–mg^–1powder,respectively; AMP + malate showed very low activity. Some combinationsexhibited linear activities with time, while others had an exponential-typeprofile. The temperature dependence of the ATP accumulationdemonstrated by the Ahrrenius plot had a double phase with atransition point at 25° C. The Ea values between 15°C and 25° C were 25 000–50 000 cal/mol, while above25° C the Ea values fluctuated between 6000 and 8000 cal/mol(depending on the substrate). The AMP + PEP combination exhibiteda single-phase profile between 15° C and 40° C, withan Ea value of 22 000 cal/mol. In the presence of some substrates,ethephon (ethylene) had a stimulatory effect and caused an increasein the Ea values at the high temperature phase. A comparisonof seed powder from dormant seeds with that from non-dormantseeds revealed that some substrate combinations accumulate ATPfaster in non-dormant seeds and others do so in dormant seeds. Key words: Arachis hypogaea, ATP, Ethylene, Dormancy, Peanut, Seed     

Long-Term Chilling of Young Tomato Plants under Low Light. IV. Differential Responses of Chlorophyll Fluorescence Quenching Coefficients in Lycopersicon Species of Different Chilling Sensitivity

Temperature dependences of chlorophyll fluorescence quenchingcoefficients were studied in the cultivated tomato (Lycopersiconesculentum) and three lines of the chilling-tolerant L.peruvianumfrom different altitudes, i.e. LA 1373 (20 m a.s.l.), LA 2157(1,650 m a.s.l.) and LA 385 (2,400 m a.s.l.). At actinic lightintensity near light saturation of photosynthesis (370 µEm^–2 s^7minus;1), photochemical quenching (qP) increasedwith increasing temperature between 5 and 30°C. The temperature,at which qP reached the numerical value 0.5 [T (qP=0.5)] decreasedby 2.5–4.5°C after a chilling treatment of 14 daysat 10°C in L. peruvianum, indicating acclimation of thephotosynthetic dark reactions in this species. The final T (qP=0.5)attained after chilling could be arranged in the order L.esculentum>LA1373>LA 2157>LA 385. The fast relaxing non-photochemicalquenching (qN) component (qf, consisting mainly of energy-dependentquenching, qE) exhibited minima near the optimum temperaturefor photosynthesis. These minima shifted to lower temperaturesupon chilling in L. peruvianum. Photoinhibitory quenching (ql)was unaffected by chilling in the high altitude lines, but-increasedstrongly in LA 1373 and L. esculentum. Under low actinic light(40 µE m^–2 s^–1), temperature dependences ofqP and qN were nearly identical in L. esculentum and LA 385and revealed abrupt changes at approx. 8°C. It is concludedthat qP and ql, measured after defined chilling treatments,are valuable screening parameters for chilling tolerance inearly growth stages of Lycopersicon plants. (Received November 2, 1993; Accepted February 28, 1994)     

Growth Responses of Two Solanum Species to Contrasting Temperatures and Irradiance Levels: Relations to Photosynthesis, Dark Respiration and Chlorophyll Fluorescence

Potato production in the tropical lowlands during the rainyseason is constrained by high temperature and low irradiance.This study examined the effect of these two variables on drymatter production and allocation, using plant growth, leaf anatomy,gas exchange and chlorophyll fluorescence measurements. Plantsof two clones, Solanum goniocalyx cv. Garhuash Huayro (GH) andDTO-33, a heat tolerant clone of S. tuberosum x S. phureja,were grown in growth chambers at 33/25 °C or 20/10 °Cday/night temperature. At each temperature, plants were grownin either 12 h high irradiance (430–450 µmol m^–2s^–1 PAR) or 12 h low irradiance (250–280 µmolm^–2 s^–1) both with a 6–h photoperiod extensionof 6 µmol m^–2 s^–1. Plants were harvested after10 d (initial harvest) and after 20 d (final harvest). By theend of the study DTO-33 had produced more dry matter and hadtuberized, whereas GH had a greater leaf area ratio (LAR) andspecific leaf area (SLA). The highest relative growth rate (RGR)was at low temperature and low irradiance, possibly due to acombination of thin leaves with a large surface area. At thehigh temperature, low irradiance had the opposite effect, producingthe lowest net assimilation rate (NAR) and lowest RGR. Bothtuber number and weight were markedly reduced by high temperature.Low irradiance, in combination with high temperature, producedvirtually no tubers. Stomatal density, which was greater onGH than in DTO-33, was increased at high temperature. When measuredat 30 °C both clones, especially DTO-33, showed heat-adaptationin terms of ability to maintain a high rate of net photosynthesisat 30 °C. Plants grown at high irr-adiance and low temperaturehad the lowest net photosynthetic rate at 30 °C. Concurrentmeasurements of chlorophyll fluorescence indicated that onlythe initial (O) fluorescence parameter was affected. The dataconfirm the field observation that reduction in potato growthat high temperature can be aggravated by lower irradiance. Thisreduction is associated with a reduced leaf area and NAR. Growth analysis, heat adaptation, light     

Dark uptake of inorganic14C in oligotrophic oceanic waters

Dark uptake of inorganic ¹⁴C by offshore plankton was measuredat two depths at 36 stations in the Atlantic Ocean from 52°Sto 26°N, mainly along 30°W. The samples were incubatedfor 2 h with and without inhibition of biological activity withHgCl₂. In addition, six time course experiments were performed.The mean dark uptake rate varied from 0.68 to 4.82 (µmolC m^–3 h^–1 over the transect and showed a significantpositive relationship with chlorophyll a. The dark uptake wasusually >5% of the maximum photosynthetic capacity (P^m),and higher values relative to P^m were associated with low valuesof P_m and not with high absolute dark values. A linear relationshipbetween dark uptake and P_m was found with a background value(y-axis intercept) of 0.51 (µmol C m^–3 h^–1and a slope of 0.77% of P^m. A major fraction of the dark signal,66–80% of the total signal, persisted in bottles treatedwith HgCl2, indicating that most of the dark signal was independentof biological activity. Time course experiments showed a lineardark uptake with time for the first hours, whereafter the uptakeceased. At stations with low concentrations of inorganic nitrogen[>1 (µmol (NH₄⁺+NO₃^–)], a second stage was observedafter 3–8 h, probably due to an increase in bacterialactivity. The results suggest three mechanisms for the darkvalue in short-term incubations in oligotrophic waters. A backgroundvalue independent of biomass and incubation time which was thedominant part of the dark signal in samples with very low phytoplanktonbiomass (>0.3 p-g Chi a 1"). Another important part was residualsof ¹⁴C associated with plankton, probably adsorbed to compoundsinside the cells. This fraction was dominant in short-term incubationsat chlorophyll concentrations >0.3 p.g Chi a H. Active uptakeby living cells (total minus ‘HgCl2 uptake‘) wasonly a minor part of the dark signal in short-term incubations,but dominated at longer incubation time (>3–9 h), probablydriven by an increase in bacterial activity. A significant enhancementof the non-photosynthetic uptake of ¹⁴C was observed in light,probably associated with a carbon-concentrating mechanism inphytoplankton or light stimulation of ß-carboxylationactivity. The results strongly suggest that dark values shouldbe subtracted from the light uptake. This correction is particularlyimportant when photosynthetic rates are low, e.g. at low lightor in short-term incubations where a time-zero background becomesa significant part of the total uptake in light. Present address: National Environmental Research Institute,Department of Marine Ecology and Microbiology, Frederiksborgvej399, PO Box 358, DK-4000 Roskilde, Denmark     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

Seasonal and interannual variability of chlorophyll a and primary production in the Equatorial Atlantic: in situ and remote sensing observations

The seasonal variability of phytoplankton in the EquatorialAtlantic was analysed using Sea-viewing Wide Field-of-view Sensor(SeaWiFS)-derived chlorophyll a (Chl a) concentration data from1998 to 2001, together with in situ Chl a and primary productiondata obtained during seven cruises carried out between 1995and 2000. Monthly averaged SeaWiFS Chl a distributions werein agreement with previous observations in the Equatorial Atlantic,showing marked differences between 10° W in the EasternTropical Atlantic (ETRA) and 25° W in the Western TropicalAtlantic (WTRA) provinces (Longhurst et al. 1995. J. PlanktonRes., 17, 1245–1271). The seasonal cycle of SeaWiFS-derivedChl a concentration calculated for 0–10° S, 0–20°W (ETRA) is consistent with in situ Chl a measurements, withvalues ranging from 0.16 mg m^–3, from February to April,to 0.52 mg m^–3 in August. Lower variability was observedin 10° N–10° S, 20–30° W (WTRA) whereminimum and maximum concentrations occurred in April (0.15 mgm^–3) and in August (0.24 mg m^–3), respectively.A significant empirical relationship between depth-integratedprimary production and in situ measured sea surface Chl a wasfound for ETRA, allowing us to estimate the seasonal cycle ofdepth-integrated primary production from SeaWiFS-derived Chla. As for Chl a, this model was verified in a small area ofthe Eastern Equatorial Atlantic (0–10° S, 0–20°W), although in this instance it was not completely able todescribe the magnitude and temporal variability of in situ primaryproduction measurements. The annual euphotic depth-integratedprimary production rate estimated for ETRA by our empiricalmodel was 1.4 Gt C year^–1, which represents 16% of theopen ocean primary production estimated for the whole AtlanticOcean.     

Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fedad libitum rations of Daphnia pulex at 4,10,15 and 18°C.Gut-residence time was also evaluated for M.relicta fed clado-ceranprey at 4, 10 and 157deg;C. Mean daily consumption (g dry weightof Daphnia g^–1 dry weight of Mysis day^–1) rangedfrom 6% at 4%C to 12% at 10°. At 18°C, Mysis feedingrate declined to 9% day1. Mean, weight-adjusted consumptionrates exhibited a ‘dome-shaped’ response in relationto water temperature. Consumption rate was highest at 10°Cand lowest at 4°C. Estimated Q₁₀ was more sensitive from4 to 10°C (Q₁₀= 3) than from 10 to 15°C (Q₁₀=1.2). Gut-residencetime for Mysis was inversely related to water temperature, implyingthat evacuation rate increases linearly with water temperature.Feeding and gut-evacuation rates become disassociated at watertemperatures >10°C. As water temperature increased above1°C, relative evacuation rate increased, whereas feedingrate declined. It is postulated that at higher water temperatures,disassociated feeding and gut-evacuation rates reduce the scopefor growth of vertically migrating Mysis and impose a physiologicalconstraint that isolates Mysis from warm, epilimnetic waterduring thermal stratification. ¹Present address: Center for Aquatic Ecology, Illinois NaturalHistory Survey, Sam Parr Biological Station, 6401 Meacham Road,Kinmundy, IL 62854, USA