Effects of Metabolic Inhibitors on the Calcification of a Freshwater Green Alga Gloeotaenium loitlesbergarianum Hansgirg. 2. Effects of Some Inhibitors of Protein Synthesis

The effects of five inhibitors of protein synthesis, viz. streptomycin,aurin tricarboxylic acid, tetracycline, chloramphenicol, andcycloheximide, on the calcification of Gloeotaenium loitlesbergarianumHansgirg, a freshwater green alga were studied. Streptomycinhad no effect while aurin tricarboxylic acid at 50 µgml^–1 and tetracyline, chloramphenicol and cycloheximideat 20 µg ml^–1 completely inhibited calcificationin the alga. High concentrations of chloramphenicol and cycloheximidewere not completely inhibitory when added 26 h and 32 h respectivelyafter the material was incubated in the induction medium. Itis concluded that the effects by these substrates are the resultsof inhibition of protein synthesis, which is directly or indirectlylinked to calcification. calcification, Gloeotaenium loitlesbergarianum Hansgirg, green alga, chlorophyceae, protein synthesis inhibitors     

Polymorphism in gloeotaenium (Chlorococcales,Chlorophyceae)

Morphological variations of Gloeotaenium loitlesbergarianum Hansgirg were studied both in cultures and in nature. In cultures, the alga exhibits considerable variation in the number of cells per colony, ranging from unicells to colonies with more than four cells. The characteristic band was also absent in cultures. In nature, colonies resembling the culture material of Gloeotaenium also occur. The morphology of the alga varies depending on the nature and composition of the nutrients available. The study shows that Gloeotaenium may exhibit polymorphism in nature as well.     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

Calcification in the Green Alga Halimeda: IV. THE ACTION OF METABOLIC INHIBITORS ON PHOTOSYNTHESIS AND CALCIFICATION

The effects of a number of metabolic inhibitors on calcificationand photosynthesis in Halimeda tuna, H. discoidea, and H. macrolobaare described. The inhibitors used are CCCP, DNP, DCMU, azide,cyanide, chloramphenicol, cycloheximide, and Diamox. The effectsof these inhibitors, although complex, are consistent with ourmodel of calcification in Halimeda. Inhibition of photosyntheticCO₂ uptake inhibits calcification as does stimulation of respiratoryCO₂ evolution (i.e. uncoupling). There is also indirect evidencefor the presence of a possible light stimulated H⁺ efflux whichinhibits calcification. The observed calcification rate is thereforethe result of a number of factors which affect the concentrationof CO^–and the pH in the intercellular space of the Halimedathallus. The results obtained with the carbonic anhydrase inhibitor Diamoxprovide further evidence for the effective separation of theintercellular space from the external medium by the appressedperipheral utricles.     

An Evaluation of the Effects of Ethylene on Carbon Assimilation in Lycopersicon esculentum Mill

Leaf and whole plant gas exchange rates of Lycopersicon esculentumMill, were studied during several days of continuous exposureto ethylene. Steady-state photosynthesis and transpiration ratesof control and ethylene-treated individual leaves were equivalent.However, the photosynthesis and transpiration rates of treatedleaves required at least five times longer to reach 50% of thesteady-state rate. This induction lag was attributed to ethylene—inducedleaf epinasty and temporary acclimation to lower incident lightlevels immediately prior to measurement of gas exchange. Thewhole plant net carbon exchange rate (NCER) of a representativetreated plant was also reduced by 51% after 24 h exposure toethylene relative to both its pre-treatment rate and that ofthe control. Ethylene exposure reduced the growth rate of thetreated plant by 50% when expressed as carbon (C) gain. Theinhibition of NCER and growth rate associated with epinastywas completely reversed when the epinastic leaves were returnedto their original positions and light interception was re-established.The results demonstrate that the inhibition of whole plant CO₂assimilation is indirect and due to reduced light interceptionby epinastic leaves. Morphological changes caused by environmentalethylene are thus shown to reduce plant C accumulation withoutinhibiting leaf photosynthesis processes per se. Key words: Ethylene, carbon assimilation, growth     

The Path of Carbon in Photosynthesis: XIII. pH EFFECTS IN C14O2 FIXATION BY SCENEDESMUS

The rates of the photosynthetic and dark fixations of C¹⁴O₂in Scenedesmus have been compared in dilute phosphate buffersranging from pH 1.6 to pH 11.4 and the amounts of carbon incorporatedinto the various products have been determined by means of theradiochromatographic method. In photosynthesis, an acid medium favours early incorporationof C¹⁴ into sucrose, polysaccharides, and the three-carbon compoundsalanine and serine. Fixation into the four-carbon compoundsmalic and aspartic acids is enhanced in an alkaline medium.Kinetic experiments at several pH values suggest that severalpaths may be available for carbon dioxide assimilation. A tentative correlation of the results with the pH optima ofsome enzymes and resultant effects upon concentrations of intermediatesis presented.     

Photosynthesis and Calcification at Cellular, Organismal and Community Levels in Coral Reefs: A Review on Interactions and Control by Carbonate Chemistry

SYNOPSIS. Photosynthesis and calcification in zooxanthellatescleractinian corals and coral reefs are reviewed at severalscales: cellular (pathways and transport mechanisms of inorganiccarbon and calcium), organismal (interaction between photosynthesisand calcification, effect of light) and ecosystemic (communityprimary production and calcification, and air-sea CO₂ exchanges). The coral host plays a major role in supplying carbon for thephotosynthesis by the algal symbionts through a system similarto the carbon-concentrating mechanism described in free livingalgal cells. The details of carbon supply to the calcificationprocess are almost unknown, but metabolic CO₂ seems to be asignificant source. Calcium supply for calcification is diffusionalthrough oral layers, and active membrane transport only occursbetween the calicoblastic cells and the site of calcification.Photosynthesis and calcification are tightly coupled in zooxanthellatescleractinian corals and coral reef communities. Calcificationis, on average, three times higher in light than in darkness.The recent suggestion that calcification is dark-repressed ratherthan light-enhanced is not supported by the literature. Thereis a very strong correlation between photosynthesis and calcificationat both the organism and community levels, but the ratios ofcalcification to gross photosynthesis (0.6 in corals and 0.2in reef communities) differ from unity, and from each otheras a function of level. The potential effect of global climatic changes (pCO₂ and temperature)on the rate of calcification is also reviewed. In various calcifyingphotosynthetic organisms and communities, the rate of calcificationdecreases as a function of increasing pCO₂ and decreasing calciumcarbonate saturation state. The calculated decrease in CaCO₃,production, estimated using the scenarios considered by theInternational Panel on Climate Change (IPCC), is 10% between1880 and 1990, and 9–30% (mid estimate: 22%) from 1990to 2100. Inadequate understanding of the mechanism of calcificationand its interaction with photosynthesis severely limits theability to provide an accurate prediction of future changesin the rate of calcification.     

In-Phase Cycling of Photosynthesis and Conductance at Saturating Carbon Dioxide Pressure Induced by Increases in Water Vapour Pressure Deficit

Bunce, J. A. 1987. In-phase cycling of photosynthesis and conductanceat saturating carbon dioxide pressure induced by increases inwater vapour pressure deficit.—J. exp. Bot. 38: 1413–1420. The leaf to air water vapour deficit was increased suddenlyfrom about 1·0 to 2·5 IcPa for single leaves ofsoybean (Glycine max L. Merr.) plants held at 30 °C, 2·0mmol m ^–2 s^–1 photosynthetic photon flux density(PPFD) and carbon dioxide pressures saturating to photosynthesis.After a lag of about 10 min, photosynthetic rate and stomatalconductance to water vapour began to decrease, and then cycledin phase with each other. The period of the cydes was about20 min. During these cycles the substomatal carbon dioxide pressurewas constant in the majority of leaves examined, and was alwaysabove saturation for photosynthesis. Epidermal impressions showedthat most stomata changed in aperture during the cycles, andthat very few were ever fully closed. Water potential measuredon excised discs changed by at most 0·1 MPa from theminima to the maxima in transpiration rate. In contrast, forleaves of sunflower (Helianthus animus L.) grown at low PPFD,the increase in VPD led to leaf wilting and decreased photosynthesis,followed by recovery of turgor and photosynthesis as stomatalconductance began to decrease. In these leaves photosynthesisand conductance then cycled approximately 180° out of phase.It is suggested that in soybeans decreased leaf conductanceinduced by high VPD provided a signal which decreased the rateof photosynthesis at carbon dioxide saturation by a mechanismthat was not related to a water deficit in the mesophyll. Key words: Photosynthesis, stomatal conductance, cycling, vapour pressure deficit     

CATALYTIC EFFECTS OF CARBON DIOXIDE IN CARBON DIOXIDE ASSIMILATING CELLS

It has been confirmed that absence of carbon dioxide may decreasethe rate of oxygen production which accompanies the photochemicalreduction of p-benzoquinone in algae and chloroplasts. Thisinfluence of carbon dioxide partial pressure does not applyto the overall oxygen yield. In the blue-green alga Anacystisnidulans the initially small carbon dioxide deficiency effectincreases with time spent in the dark. The deterioration ofreaction rates is counteracted by light. There seems to be nodirect connection or interdependence between the photosyntheticreduction of carbon dioxide and the sensitivity of some partof the photochemical mechanism to loss of carbon dioxide. Notonly does addition of quinone to living cells in these experimentsdestroy their capacity for photosynthesis, but mutant cellsthat never had this capacity still retain the sensitivity towardslack of carbon dioxide when tested for their ability to reducequinone. Many different metabolic reactions have been seen topossess such dependency on traces of carbon dioxide, also innon-photosynthetic cells and tissues. The explanation for "catalytic"effects of carbon dioxide ought to be a general one–suchas an influence on the efficiency of certain phosphorylationswhich occur everywhere in the living world. ¹ Dedicated to Prof. H. TAMIYA on the occasion of his 60th birthday.These studies were aided by contract NONR 988 (10) between theOffice of Naval Research, Department of the Navy, and the FloridaState University, respectively. ² Present address: Charles F. KETTERING Research Laboratories,Yellow Springs, Ohio. (Received December 7, 1962; )     

Calcification in the Green Alga Halimeda: III. THE SOURCES OF INORGANIC CARBON FOR PHOTOSYNTHESIS AND CALCIFICATION AND A MODEL OF THE MECHANISM OF CALCIFICATION

Calcification and photosynthetic rates in Halimeda tuna weremeasured by the ¹⁴C method under conditions of differing pHand total inorganic carbon (CO₂) concentrations. The effectsof pH and CO₂ on photosynthesis and respiration were also monitoredwith a polarographic O₂ electrode. The results obtained indicatethat the intercellular pH and CO₂ differ from those of the externalmedium. Experiments carried out over a range of pH values show thatHalimeda can use for photosynthesis. Photosynthesis appears to stimulate calcification by removing CO₂ from theintercellular spaces. As these spaces are isolated from theexternal sea water by the layer of cell wall of the adpressedperipheral utricles, the removal of CO₂ results in a rise in[] and a rise in pH. This results in an increased rate of CaCO₃ precipitation. Respiratory CO₂ evolution has aninhibitory effect on calcification by decreasing the pH and[]. A model for calcification in Halimeda is proposed based on theresults of this and previous papers. Calcification in Halimedais seen to be a result of the anatomy of the thallus in whichthe sites of calcification are within a semi-isolated chamberwhere removal or addition of CO₂ due to photosynthesis or respirationcan effectively change [CO] thereby resulting in precipitation of CaCO₃. In the Appendix to this paper theoreticalcalculations illustrate the effects of CO₂, , and removal or addition in a closed system on the relative concentrations of the other inorganic carbonspecies.     

Dependence of phytoplankton assimilation quotients on light and nitrogen source: implications for oceanic primary productivity

Photosynthetic production of oxygen by phytoplankton assemblagedominated by Peridinium in Lake Kinneret, Israel, generallyexceeds the molar equivalent rate of carbon assimilation. Carbonassimilation occurs only if oxygenic photosynthesis exceedsa light-dependent threshold. Assimilation quotients (mol C molO₂^–1) are a variable function of irradiance, and typicallyonly about one-half of the photoreductant produced during oxygenicphotosynthesis is used for reduction of carbon dioxide. Mostof the residual oxygenic photoreductant probably is used forlight-dependent reduction of nitrate, which competes with carbondioxide for oxygenic photoreductant. Nitrate is an importantsource of nitrogen for this algal assemblage, and light-dependentnitrate reduction probably is much larger than carbon dioxidereduction at lowest irradiances in the euphotic zone. Oxygenproduction also may be much larger than carbon assimilationat low light levels in other environments where oxidized formsof nitrogen are important nitrogenous nutrients for phytoplankton,as in the lower euphotic zone of the sea, where low rates ofcarbon assimilation by phytoplankton have been thought to beinconsistent with the amount of oxygen that accumulates duringsummer.     

Evidence for the participation of the reductive pentose phosphate cycle in photoreduction and the oxyhydrogen reaction

The assimilation of ¹⁴C-sodium bicarbonate has been measured in Scenedesmus obliquus as 1) photosynthesis, 2) photoreduction (light dependent incorporation of carbon dioxide by hydrogen adapted cells under conditions where photosynthesis is inoperative), and 3) the oxyhydrogen reaction (dark assimilation of carbon dioxide by hydrogen adapted cells in an atmosphere of hydrogen and 1% oxygen). Degradation of the glucose formed in each of these reactions using the Leuconostoc technique establishes the participation of the reductive pentose phosphate cycle.     

Nitrite Uptake into Intact Pea Chloroplasts : II. Influence of Electron Transport Regulators, Uncouplers, ATPase and Anion Uptake Inhibitors and Protein Binding Reagents

The relationship between net nitrite uptake and its reduction in intact pea chloroplasts was investigated employing electron transport regulators, uncouplers, and photophosphorylation inhibitors. Observations confirmed the dependence of nitrite uptake on stromal pH and nitrite reduction but also suggested a partial dependance upon PSI phosphorylation. It was also suggested that ammonia stimulates nitrogen assimilation in the dark by association with stromal protons. Inhibition of nitrite uptake by N-ethylmaleimide and dinitrofluorobenzene could not be completely attributed to their inhibition of carbon dioxide fixation. Other protein binding reagents which inhibited photosynthesis showed no effect on nitrite uptake, except for p-chlormercuribenzoate which stimulated nitrite uptake. The results with N-ethylmaleimide and dinitrofluorobenzene tended to support the proposed presence of a protein permeation channel for nitrite uptake in addition to HNO₂ penetration. On the basis of a lack of effect by known anion uptake inhibitors, it was concluded that the nitrite uptake mechanism was distinct from that of phosphate and chloride/sulfate transport.     

Acclimation of photosynthesis to low temperature in Spinacia oleracea L. II. Effects of nitrogen supply

The photosynthetic capacity of leaves of N-sufficent plantsof Spinacia oleracea L. increases following transfer a constanttemperature of 10C for 10 d compared to plants maintained at25C. The effects of nitrogen nutrition on this low temperatureacclimation have been investigated in respect of CO₂ assimilation,the activities and activation states of key enzymes and thepartitioning of recently fixed carbon. N-deficiency greatlyrestricted acclimation of photosynthetic CO₂ assimilation tolow temperature at both ambient and at saturating CO₂ concentrations,indicating a restriction on accilmatory changes in both ribulose1,5-bisphosphatecarboxylase-oxygenase (Rubisco) and the reactions of ribulose1,5-bisphosphateregeneration. Nitrogen limitation led to an increase in thepartitioning of recently-fixed carbon into starch. Total proteinincreased during acclimation in both N-sufficient and N-deficientleaves and was much less affected than were the activities ofenzymes. Increases in the activation state of Rubisco and thestromal fructose-1,6-bisphosphatase occurred in response tolow temperature, but increases in the activities of Rubisco,sucrose-phosphate synthase or the cytosolic fructose1,6-bisphosphatasecould not be sustained in N-deficient plants throughout theperiod of acclimation, although the activities of these enzymesdeclined less precipitately than in non-acclimated N-deficientplants. These data are all consistent with the view that increasesin the activities of key enzymes of carbon assimilation area pre-requisite for acclimation to low temperature and thatthese increases are restricted under N-limitation. Key words: Low temperature, nitrogen, photosynthesis, Rubisco, sucrose-phosphate synthase     

Primary Production and Calcification by the Soritid Foraminifer Archais angulatus (Fichtel & Moll)*

SYNOPSIS. Symbiosis between Chlamydomonas hedleyi (Lee, Crockett, Hagen & Stone) and Archais angulatus (Fichtel & Moll) was examined during laboratory studies of primary production and light-enhanced calcification. Photosynthesis and calcification are directly proportional to light intensity in the range of 0–200 μEinsteins m^-2 sec^-1. Calcification in the light is directly proportional to photosynthesis and proceeds at rates that are 2–3 times that observed in the dark. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), in concentrations of 1–100 μM, completely inhibits photosynthesis and light-enhanced calcification. Calcification of the foraminiferan test is therefore due to the photosynthetic activity of the symbiote. Calcification rates for foraminifers incubated in the dark or with DCMU are not significantly different from the calcification rates obtained for dead foraminifers. Rates of calcification obtained with ⁴⁵Ca are twice that obtained with ¹⁴C.     

Short-Term Fixation of 14Carbon by the Submerged Aquatic Angiosperm Potamogeton pectinatus

In ¹⁴C fixation experiments, 3-phosphoglyceric acid was thefirst product of carbon assimilation in the light in Potamogetonpectinatus. The pattern of early ¹⁴C-labelled compounds wasthe same over a range of pH values of the medium from 3.5 to8.1. Rates of ¹⁴C incorporation declined with increasing pHof the medium indicating that free CO₂ is the major exogenoussource of carbon for photosynthesis in Potamogeton pectinatus.     

Effects of Light and Bicarbonate on Membrane Potential in Potamogeton schweinfurthii (Benn)

Measurements have been made of photosynthesis by submerged leavesof the aquatic angiosperm, Potamogeton schweinfurthii, and ofmembrane potential differences between the interior of leafcells and various media. Bicarbonate may be absorbed and usedfor photosynthesis with concomitant export of hydroxyl ionshowever much molecular carbon dioxide is also present and beingabsorbed. The green cells are temporarily depolarized upon illuminationand hyperpolarized on darkening. These potential changes areassociated with absence and presence of bicarbonate and aretentatively interpreted in terms of active transport mechanismsfor bicarbonate and hydroxyl ions.     

Effects of Nitrogen Nutrition on Leaf Expansion and Photosynthesis of Trifolium subterraneum L. 1. Comparison between Different Levels of Nitrogen Supply

Growth analysis showed that reductions in the relative growth-rateof subterranean clover plants (cv. Mt. Barker), even those dueto moderate nitrogen deficiencies, were reflected in reductionsof the leaf-area ratio and particularly of the net assimilationrate. A decline in nitrogen supply in the culture solutions was foundto depress net rates of carbon dioxide uptake per unit leafarea and leaf expansion per plant to about the same extent,even at moderate levels of nitrogen stress. Four days aftertransfer of plants grown with adequate nitrogen to solutionswithout nitrogen, leaf area and net carbon dioxide uptake haddeclined to 84 per cent and 89 per cent of the values for thecontrol plants. After a further 4 days these values had decreasedto 71 per cent and 52 per cent respectively. When net carbon dioxide uptake was expressed per unit weightof chlorophyll, the effect of changes in nitrogen supply onnet photosynthesis largely disappeared, indicating a close relationshipwith the chlorophyll content of the leaves. However, anotherand perhaps more direct effect of nitrogen on photosynthesiswas suggested by the fact that, during the early stages of recoveryfrom a severe nitrogen stress, photosynthesis began to increasebefore the chlorophyll content of the leaves.     

Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Vegetative crops of chrysanthemum were grown for 5 or 6 weekperiods in daylit assimilation chambers. Crop responses to differentradiation levels and temperatures were analysed into effectson dry matter partitioning, specific leaf area, leaf photosynthesisand canopy light interception. The percentage of newly formed dry matter partitioned to theleaves was almost constant, although with increasing radiationor decreasing temperature, a greater percentage of dry matterwas partitioned to stem tissue at the expense of root tissue.There was a positive correlation between the percentage of drymatter in shoot material and the overall carbon: dry matterratio. Canopy photosynthesis was analysed assuming identical behaviourfor all leaves in the crop. Leaf photochemical efficiency wasonly slightly affected by crop environment. The rate of grossphotosynthesis per unit leaf area at light saturation, P_A (max),increased with increasing radiation integral, but the same parameterexpressed per unit leaf dry matter, P_w (max) was almost unaffectedby growth radiation. In contrast, P_A (max) was hardly affectedby temperature but P_w (max) increased with increasing growthtemperature. This was because specific leaf area decreased withdecreasing temperature and increased with decreasing radiation.There was a positive correlation between canopy respirationintegral and photosynthesis integral, and despite a four-foldchange in crop mass during the experiments, the maintenancecomponent of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variationwith radiation integral but was negatively correlated with temperature.This decrease in the efficiency of the canopy at interceptingradiation exactly cancelled the increase in specific carbonassimilation rate that occurred with increasing growth temperature,giving a growth rate depending solely on the incident lightlevel. Chrysanthemum, dry matter partitioning, photosynthesis, specific leaf area     

Ectopic expression of C 4 photosynthetic pathway genes improves carbon assimilation and alleviate stress tolerance for future climate change

Alteration in atmospheric carbon dioxide concentration and other environmental factors are the significant cues of global climate change. Environmental factors affect the most fundamental biological process including photosynthesis and different metabolic pathways. The feeding of the rapidly growing world population is another challenge which imposes pressure to improve productivity and quality of the existing crops. C4 plants are considered the most productive, containing lower photorespiration, and higher water-use & N-assimilation efficiencies, compared to C3 plants. Besides, the C4-photosynthetic genes not only play an important role in carbon assimilation but also modulate abiotic stresses. In this review, fundamental three metabolic processes (C4, C3, and CAM) of carbon dioxide assimilation, the evolution of C4-photosynthetic genes, effect of elevated CO2 on photosynthesis, and overexpression of C4-photosynthetic genes for higher photosynthesis were discussed. Kranz-anatomy is considered an essential prerequisite for the terrestrial C4 carbon assimilation, but single-celled C4 plant species changed this well-established paradigm. C4 plants are insensitive to an elevated CO2 stress condition but performed better under stress conditions. Overexpression of essential C4-photosynthetic genes such as PEPC, PPDK, and NADP-ME in C3 plants like Arabidopsis, tobacco, rice, wheat, and potato not only improved photosynthesis but also provided tolerance to various environmental stresses, especially drought. The review provides useful information for sustainable productivity and yield under elevated CO2 environment, which to be explored further for CO2 assimilation and also abiotic stress tolerance. Additionally, it provides a better understanding to explore C4-photosynthetic gene(s) to cope with global warming and prospective adverse climatic changes.