Showing papers on "Photosynthesis published in 1977"

Comparative photosynthesis of sun and shade plants.

Abstract: INTRODUCTION 355 SUN AND SHADE SPECIES . 356 Light Saturation Characteristics 356 Pigment Content and Leaf Anatomy ..... 357 Chloroplast Structure 358 Parameters Influencing Photosynthetic Rates 359 CO2 Diff usion and the Carboxylation of Ribulose Diphosphate 360 Photosynthetic Electron Transport 361 Electron Transport Components ... 361

Heat-induced changes of chlorophyll fluorescence in intact leaves correlated with damage of the photosynthetic apparatus.

Abstract: Methods were developed to measure chlorophyll fluorescence yield of intact leaf tissue during heat treatment under varying conditions of light intensity and photosynthetic activity. Fluorescence yield of a dark-adapted leaf increases by 2- to 3-fold with an increase of temperature into the region where heat-damage occurs. The temperatures of the fluorescence transition correlate well with the temperatures where quantum yield of CO2 fixation is irreversibly depressed. Fluorescence-temperature (F-T) curves allow ranking of different species according to their heat sensitivity. Within a single species acclimation to different growth temperatures is reflected by shifts of the transition temperatures in the F-T curves. When F-T curves are recorded in the steady light states at increasing light intensities, substantial shifts (up to 6°C) of transition temperatures to higher values are observed. Quantum yield measurements of CO2 fixation confirm that hight-light conditions protect from heat-damage. It is suggested that chlorophyll acts as an intrinsic fluorescence probe of the thylakoid membrane and responds to the same changes which cause irreversible denaturation of photosynthetic enzymes.

A cost-income model of leaves and roots with special reference to arid and semiarid areas

Abstract: The richness of plant-life forms, ranging from unicellular algae to large trees, from trailing herbs to large climbing vines, and from ephemerals to long-lived perennials, suggests that a variety of environmental factors exert important influences on plant shapes (Terborgh 1973). In this paper we describe a model in which the inevitable association between water loss and entrance of carbon dioxide through stomates, together with cell-morphological and physiological traits that affect these exchanges, prevent any one plant-life form from being the best adapted to more than a fraction of the earth's complex patterns of temperature and moisture availability. These relationships may also explain apparently stable mixtures of plants with different life forms in a single environment. The tight linking of water loss and carbon uptake affects all aspects of the total photosynthetic and materials uptake system of vascular plants, because reducing water loss lowers rates of carbon uptake and hence lowers rates of net photosynthesis per unit area of photosynthesizing surface. The combination of characters that yields maximum net photosynthesis per unit time under moist conditions reduces the maximum rate under drier conditions, and vice versa. There are, of course, mechanisms, such as C4 photosynthesis and opening stomata only when atmospheric humidity is high, which reduce water loss per molecule of carbon fixed, but these mechanisms are of limited effectiveness and have associated costs. Any model of natural selection assumes both some "goal" that is being optimized (or maximized) and the constraints within which the organisms operate. A reasonable short-range goal for plants might be the maximization of photosynthetic rate; a plant capable of increasing photosynthesis within the constraints of its available resources and the physical environment should gain advantages in competition with other plants, defenses against herbivores, and should have more energy to devote to reproduction. We assume in our model that total fitness is strongly correlated with net gain in calories and that it is reasonable to treat allocations of resources to leaves, stems, and roots in terms of calories. Thus, we ignore other potentially significant factors, e.g., nonuniform mortality risks due to herbivory or pathogens, which should influence the

Photosynthesis in Salt-Stressed Grapevines

Abstract: Rooted cuttings of grapevine (Vitis vinifera L. cv. Sultana syn. Thompson Seedless) were grown in sand culture irrigated with nutrient solution containing 1-125 mM NaCl. The effect of salinity on vine growth and photosynthesis is described. Salinity led to reduced growth where foliar symptoms of salt toxicity were absent. Rates of CO2 fixation decreased with increasing levels of chloride in leaves. This decrease in photosynthesis could be largely attributed to increased residual (mesophyll) resistance to CO2 fixation. Radiotracer studies showed that salt stress led to the accumulation of label in intermediates of the glycollate pathway. Salt-stressed leaves contained decreased amounts of sucrose and starch, but increased levels of reducing sugars.

Occurrence of facultative anoxygenic photosynthesis among filamentous and unicellular cyanobacteria.

Abstract: Eleven of 21 cyanobacteria strains examined are capable of facultative anoxygenic photosynthesis, as shown by their ability to photoassimilate CO2 in the presence of Na2S, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 703-nm light. These include different cyanobacterial types (filamentous and unicellular) of different growth histories (aerobic, anaerobic, and marine and freshwater). Oscillatoria limnetica, Aphanothece halophytica (7418), and Lyngbya (7104) have different optimal concentrations of Na2S permitting CO2 photoassimilation, above which the rate decreases: 3.5, 0.7, and 0.1 mM, respectively. In A. halophytica, for each CO2 molecule photoassimilated two sulfide molecules are oxidized to elemental sulfur, which is excreted from the cells.The ecological and evolutionary significance of anoxygenic photosynthesis in the cyanobacteria is discussed.

Spatial relationship of photosystem I, photosystem II, and the light-harvesting complex in chloroplast membranes.

Abstract: We have previously demonstrated (Armond, P A, C J Arntzen, J-M Briantais, and C Vernotte 1976 Arch Biochem Biophys 175:54-63; and Davis, D J, P A Armond, E L Gross, and C J Arntzen 1976 Arch Biochem Biophys 175:64-70) that pea seedlings which were exposed to intermittent illumination contained incompletely developed chloroplasts These plastids were photosynthetically competent, but did not contain grana We now demonstrate that the incompletely developed plastids have a smaller photosynthetic unit size; this is primarily due to the absence of a major light-harvesting pigment-protein complex which is present in the mature membranes Upon exposure of intermittent-light seedlings to continuous white light for periods up to 48 h, a ligh-harvesting chlorophyll-protein complex was inserted into the chloroplast membrane with a concomitant appearance of grana stacks and an increase in photosynthetic unit size Plastid membranes from plants grown under intermediate light were examined by freeze-fracture electron microscopy The membrane particles on both the outer (PF) and inner (EF) leaflets of the thylakoid membrane were found to be randomly distributed The particle density of the PF fracture face was approx four times that of the EF fracture face While only small changes in particle density were observed during the greening process under continuous light, major changes in particle size were noted, particularly in the EF particles of stacked regions (EFs) of the chloroplast membrane Both the changes in particle size and an observed aggregation of the EF particles into the newly stacked regions of the membrane were correlated with the insertion of light-harvesting pigment-protein into the membrane Evidence is presented for identification of the EF particles as the morphological equivalent of a "complete" photosystem II complex, consisting of a phosochemically active "core" complex surrounded by discrete aggregates of the light-harvesting pigment protein A model demonstrating the spatial relationships of photosystem I, photosystem II, and the light-harvesting complex in the chloroplast membrane is presented

Internal Leaf Area and Cellular CO2 Resistance: Photosynthetic Implications of Variations with Growth Conditions and Plant Species

Abstract: The influences of illumination, temperature, and soil water potential during development on leaf thickness, mesophyll cell wall area per unit leaf area (Ames/A), and the cellular CO2, resistance expressed on a mesophyll cell wall area basis (rCO2cell,) were examined for Plectranthus parviflorus Henckel. Although the ranges of all three growth conditions caused at least 9-fold variations in the leaf biomass produced in 4 weeks, only the illumination had a major effect on internal leaf morphology, e.g. the thickness went from 279 to 831 μm and Ames/A from 10.5 to 34.8 as the photosynthetically active radiation was raised from 3 to 53 nEinsteins cm−2 s−1, while rCO2cell remained close to 154 s cm−1. Variations in the growth temperature, soil water potential, and the nutritional status of the plant, affected photosynthesis mainly by changes in rCO2cell. To compare the influence of internal leaf area on photosynthesis for other plants, especially those with low Ames/A values, the maximum rates of CO2 uptake at light saturation and photosynthetically optimal temperatures were also determined for a moss, Mnium ciliare (C. Muell.) Schimp., and two ferns, Adiantum decorum Moore and Alsophila australe R. Br. As Ames/A went from 2.00 for the moss to 3.8, 7.5, 11.7, and 20.8 for the fens, the illumination at light saturation and the maximum rate of photosynthesis both progressively increased. The cellular CO2 resistance, which theoretically might have a lower limit of 20 s cm−1, ranged from 85 to 190 s cm−1.

Blue-Green Algae

Abstract: The blue-green algae represent a unique stage in the evolution of plant life. The cyanophyta are clearly procaryotic organisms and so they might well be called blue-green bacteria. However they are the only procaryotes able to produce oxygen from water so their photosynthetic activity is like that of the higher plants (Krogmann, 1973). Before making any generalizations about blue-green algal photosynthesis it is important to note that there are between one and two thousand species of blue-green algae and very few have been examined in the laboratory. The taxonomy of these algae is not at all clear since their morphology is simple and their physiology is difficult. Thus there is as yet no clear choice for the best blue-green algae to use for studying photosynthesis nor any assurance that the best organism would be representative of all blue-greens. At present all results should be attributed only to the species from which they have been obtained and even then further qualified in that these results may be limited to a particular strain, culture or set of growth conditions. One might have been tempted to conclude that some blue-green algae contained no ferredoxin prior to the observation that this protein disappears promptly from iron deficient cells. The ease of extraction of a given enzyme might vary greatly depending on some yet to be recognized properties of the membrane. Presently it appears that plastocyanin can be isolated from only a few blue-greens but this may be due either to the absence of the proper gene or to some difficulties that confound the isolation procedure.

Net Photosynthesis, Electron Transport Capacity, and Ultrastructure of Pisum sativum L. Exposed to Ultraviolet-B Radiation

Abstract: Pisum sativum L. was exposed to ultraviolet-B (UV-B) radiation (280-315 nm) in greenhouse and controlled environment chambers to examine the effect of this radiation on photosynthetic processes. Net photosynthetic rates of intact leaves were reduced by UV-B irradiation. Stable leaf diffusion resistances indicated that the impairment of photosynthesis did not involve the simple limitation of CO2 diffusion into the leaf. Dark respiration rates were increased by previous exposure to this radiation. Electron transport capacity as indicated by methylviologen reduction was also sensitive to UV-B irradiation. The ability of ascorbate-reduced 2,6-dichlorophenolindophenol to restore much of the electron transport capacity of the UV-B-irradiated plant material suggested that inhibition by this radiation was more closely associated with photosystem II than with photosystem I. Electron micrographs indicated structural damage to chloroplasts as well as other organelles. Plant tissue irradiated for only 15 minutes exhibited dilation of thylakoid membranes of the chloroplast in some cells. Some reduction in Hill reaction activity was also evidenced in these plant materials which had been irradiated for periods as short as 15 minutes.

Effects of Light, Carbon Dioxide, and Temperature on Photosynthesis, Oxygen Inhibition of Photosynthesis, and Transpiration in Solanum tuberosum

Abstract: Individual leaves of potato (Solanum tuberosum L. W729R), a C(3) plant, were subjected to various irradiances (400-700 nm), CO(2) levels, and temperatures in a controlled-environment chamber. As irradiance increased, stomatal and mesophyll resistance exerted a strong and some-what paralleled regulation of photosynthesis as both showed a similar decrease reaching a minimum at about 85 neinsteins.cm(-2).sec(-1) (about (1/2) of full sunlight). Also, there was a proportional hyperbolic increase in transpiration and photosynthesis with increasing irradiance up to 85 neinsteins.cm(-2).sec(-1). These results contrast with many C(3) plants that have a near full opening of stomata at much less light than is required for saturation of photosynthesis.Inhibition of photosynthesis by 21% O(2) was nearly overcome by a 2-fold increase in atmospheric levels of CO(2) (about 1,200 ng.cm(-3)). Photosynthesis at 25 C, high irradiance, 2.5% O(2) and atmospheric levels of CO(2) was about 80% of the CO(2)-saturated rate, suggesting that CO(2) can be rate-limiting even without O(2) inhibition of photosynthesis. With increasing CO(2) concentration, mesophyll resistance decreased slightly while stomatal resistance increased markedly above 550 ng.cm(-3) which resulted in a significant reduction in transpiration.Although potato is a very productive C(3) crop, there is substantial O(2) inhibition of photosynthesis. The level of O(2) inhibition was maximum around 25 C but the percentage inhibition of photosynthesis by O(2) increased steadily from 38% at 16 C to 56% at 36 C. Photosynthesis and transpiration showed broad temperature optima (16-25 C). At higher temperatures, both the increased percentage inhibition of photosynthesis by O(2) and the increased stomatal resistance limit photosynthesis, while increased stomatal resistance limits transpiration. Water use efficiency, when considered at a constant vapor pressure gradient, increased with increasing irradiance, CO(2) concentration, and temperature.

Carbon balance, productivity, and water use of cold-winter desert shrub communities dominated by C3 and C4 species.

Abstract: Common generalizations concerning the ecologic significance of C4 photosynthesis were tested in a study of plant gas exchange, productivity, carbon balance, and water use in monospecific communities of C3 and C4 salt desert shrubs. Contrary to expectations, few of the hypotheses concerning the performance of C4 species were supported. Like the C3 species, Ceratoides lanata, the C4 shrub, Atriplex confertifolia, initiated growth and photosynthetic activity in the cool spring months and also exhibited maximum photosynthetic rates at this time of year. To compete successfully with C3 species, Atriplex may have been forced to evolve the capacity for photosynthesis at low temperatures prevalent during the spring when moisture is most abundant. Maximum photosynthetic rates of Atriplex were lower than those of the C3 species. This was compensated by a prolonged period of low photosynthetic activity in the dry late summer months while Ceratoides became largely inactive. However, the annual photosynthetic carbon fixation per ground area was about the same in these two communities composed of C3 and C4 shrubs. The C4 species did not exhibit greater leaf diffusion resistance than the C3 species. The photosynthesis/transpiration ratios of the two species were about the same during the period of maximum photosynthetic rates in the spring. During the warm summer months the C4 species did have superior photosynthesis/transpiration ratios. Yet, since Ceratoides completed a somewhat greater proportion of its annual carbon fixation earlier in the season, the ratio of annual carbon fixation/transpiratory water loss in the two communities was about the same. Atriplex did incorporate a greater percentage of the annual carbon fixation into biomass production than did Ceratoides. However, this is considered to be a reflection of properties apart from the C4 photosynthetic pathway. Both species displayed a heavy commitment of carbon to the belowground system, and only about half of the annual moisture resource was utilized in both communities.

Oxygen Inhibition of Photosynthesis I. Temperature Dependence and Relation to O2/CO2 Solubility Ratio

Abstract: The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O2 in the C3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O2/CO2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O2 and CO2 in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O2/CO2 can be increased by increased leaf temperature under constant atmospheric levels of O2 and CO2 (since O2 is relatively more soluble than CO2 with increasing temperature); by increasing the relative levels of O2/CO2 in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O2/CO2 is kept constant, as leaf temperature is increased, by varying the levels of O2 or CO2 in the atmosphere, then the percentage inhibition of photosynthesis by O2 is similar. The decreased solubility of CO2 relative to O2 (decreased CO2/O2 ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O2 under atmospheric conditions with increasing temperature.

Photosynthesis and photorespiration in algae.

Abstract: The CO2 exchange of several species of fresh water and marine algae was measured in the laboratory to determine whether photorespiration occurs in these organisms. The algae were positioned as thin layers on filter paper and the CO2 exchange determined in an open gas exchange system. In either 21 or 1% O2 there was little difference between 14CO2 and 12CO2 uptake. Apparent photosynthesis was the same in 2, 21, or 50% O2. The compensation points of all algae were less than 10 μl 1−1. CO2 or 14CO2 evolution into CO2-free air in the light was always less than the corresponding evolution in darkness. These observations are inconsistent with the proposal that photorespiration exists in these algae.

Acclimation of Photosynthetic and Respiratory Carbon Dioxide Exchange to Growth Temperature in Atriplex lentiformis (Torr.) Wats.

Abstract: Atriplex lentiformis plants collected from coastal and desert habitats exhibit marked differences in capacity to adjust photosynthetic response to changes in growth temperature. Plants from desert habitats grown at 43 C day/30 C night temperatures had higher CO 2 uptake rates at high temperatures but reduced rates at low temperatures as compared to plants grown at 23 C day/18 C night temperatures. In contrast, growth of the coastal plants at high temperatures resulted in markedly reduced photosynthetic rates at all measurement temperatures. Leaf conductances to CO 2 were not important in controlling either the differences in the temperature dependence of net CO 2 uptake or the differences in photosynthetic capacities at any measurement temperature. At low measurement temperatures, differences in photosynthetic capacities among plants acclimated to the contrasting growth regimes were correlated with differences in leaf ribulose diphophate carboxylase activities. At high measurement temperatures, the improved net photosynthetic performance of the high temperature acclimated desert plants appeared to be due to a combination of decreased respiration rates, decreased temperature dependence of respiration, and an apparent increased thermal stability of photosynthetic CO 2 exchange.

Hydrogen production by nitrogen-starved cultures of Anabaena cylindrica.

Abstract: Nitrogen-starved cultures of the alga Anabaena cylindrica 629 produced hydrogen and oxygen continuously for 7 to 19 days. Hydrogen production attained a maximum level after 1 to 2 days of starvation and was followed by a slow decline. The maximum rates were 30 ml of H2 evolved per liter of culture per h or 32 mul of H2 per mg of dry weight per h. In 5 to 7 days the rate of H2 evolution by the more productive cultures fell to one-half its maximum value. The addition of 10(-4) to 5 X 10(-4) M ammonium increased the rate of oxygen evolution and the total hydrogen production of the cultures. H2-O2 ratios were 4:1 under conditions of complete nitrogen starvation and about 1.7:1 after the addition of ammonium. Thus, oxygen evolution was affected by the extent of the nitrogen starvation. Thermodynamic efficiencies of converting incident light energy to free energy of hydrogen via algal photosynthesis were 0.4%. Possible factors limiting hydrogen production were decline of reductant supply and filament breakage. Hydrogen production by filamentous, heterocystous blue-green algae could be used for development of a biophotolysis system.

An annual carbon budget for the kelp Laminaria longicruris

Abstract: Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant Annual net assimilation was 68 mgC per cm2 of frond surface (71 cal cm-2) Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth

Water Stress Effects on the Content and Organization of Chlorophyll in Mesophyll and Bundle Sheath Chloroplasts of Maize

Abstract: The consequences of drought stress on the organization of chlorophyll into photosynthetic units and on the chlorophyll-protein composition of mesophyll and bundle sheath chloroplasts of Zea mays L. were studied. It was found that the majority of chlorophyll lost in response to water stress occurs in the mesophyll cells with a lesser amount being lost from the bundle sheath cells. All of the chlorophyll loss could be accounted for by reduction in the lamellar content of the light-harvesting chlorophyll a/b-protein, a rather specific target for water stress. The decreased content of this chlorophyll-protein accounts for the elevated chlorophyll a/b ratios and the reduced photosynthetic unit sizes of the two cell types in stressed plants. The implications of the selective catabolism of this major membrane component are discussed.

The relationship between chlorophyll content and rate of photosynthesis in soybeans

Abstract: Photosynthetic rate of soybeans (on a leaf area basis, PA) estimated from the incorporation of 14CO2 under field conditions was highly correlated with chlorophyll content of the side leaflets of th...

Effect of blue‐green light on photosynthetic pigments and chloroplast structure in unicellular marine algae from six classes1

Abstract: The photosynthetic pigments of 17 species of unicellular marine algae grown in white and blue-green light were examined. Blue-green light (400 μW·cm−2; 12:12 LD cycle) caused major chlorophyll increases (55–146%) in five diatoms, one dinoflagellate and one cryptomonad; minor chlorophyll increases (17–39%) in two diatoms, two dinoflagellates, one prymnesiophyte (haptophyte), one chrysophyte and one chlorophyte; and no chlorophyll increase in two diatoms and one pyrmnesiophyte (haptophyte). The relative proportions of major chlorophylls and carotenoids did not change, but in six of eight species tested small increases in the concentration of chlorophyll c occurred. Blue-green light caused a small increase in the concentration of phycoerythrin relative to chlorophyll a in the cryptomonad. A larger number of thylakoids per chloroplast were observed in six species grown in blue-green light compared to white light controls. The ultrastructure changes observed depended not only on the magnitude of the chlorophyll increase but also on the architecture of the chloroplast.

Ontogenetic Interactions between Photosynthesis and Symbiotic Nitrogen Fixation in Legumes

Abstract: Photosynthetic data collected from Pisum sativum L. and Phaseolus vulgaris L. plants at different stages of development were related to symbiotic N2 fixation in the root nodules. The net carbon exchange rate of each leaf varied directly with carboxylation efficiency and inversely with the CO2 compensation point. Net carbon exchange of the lowest leaves reputed to supply fixed carbon to root nodules declined in parallel with H2 evolution from root nodules. The decrease in H2 evolution also coincided with the onset of flowering but preceded the peak in N2 fixation activity measured by acetylene-dependent ethylene production. A result of these changes was that the relative efficiency of N2 fixation in peas increased to 0.7 from an initial value of 0.4. The data reveal that attempts to identify photosynthetic contributions of leaves to root nodules will require careful timing and suggest that the relative efficiency of N2 fixation may be influenced by source-sink relationships.

Characterization of Photosynthetic Rhythms in Marine Dinoflagellates: II. Photosynthesis-Irradiance Curves and in Vivo Chlorophyll a Fluorescence

Abstract: Using data from light-dark cultures of Gonyaulax polyedra entrained to a 24-hour cycle, whole cell absorption curves and photosynthesis-irradiance curves were constructed for various circadian times. While whole cell absorbance and half-saturation constants of photosynthesis showed no statistical difference that could be directly related to the photosynthetic rhythm, the initial slope of the photosynthesis-irradiance curve was a time-dependent parameter which altered in direct proportion to the change in photosynthetic capacity. The results indicated a temporal change in the relative quantum yield of photosynthesis, and the circadian rhythmicity of light-limited photosynthesis was established under constant conditions. Circadian rhythmicity was detected in room temperature chlorophyll fluorescence yield. Low temperature fluorescence kinetics also showed fluctuations. The results suggest that regulation of photosynthesis by the biological clock of Gonyaulax may be mediated through the membrane-bound light reactions and a partial explanation of the underlying mechanism is proposed.

Structure and molecular organization of the photosynthetic accessory pigments of cyanobacteria and red algae

Abstract: Cyanobacteria (blue-green algae) and Rhodophyta (red algae) contain high concentrations of photosynthetic accessory pigments (phycobiliproteins) which trap light energy in the region between 400 and 650 nm. The electronic excitation energy is then transferred along a chain of these pigments to the reaction center chlorophyll of Photosystem II by a radiationless induced resonance process.

Plant crops as a source of fuel and hydrocarbon-like materials.

Abstract: Chemical analyses have been made of a number of plant species in order to assess their suitability as renewable sources of hydrocarbon-like photosynthetic products. Yields of rubber and wax, glycerides, isoprenoids, and other terpenoids were estimated. Individual sterols were identified in latex from some species.

Photosynthesis, photorespiration, and dark respiration in eight species of algae

Abstract: The rates of photosynthesis and dark respiration for 7 marine algae and 1 fresh-water alga were measured and compared. The dinoflagellates Glenodinium sp. and zooxanthellae have high dark respiration rates relative to photosynthetic rates, which may decrease their net growth rates. Photorespiration in the 8 algal species was studied by examining the effects of the concentration of oxygen on the rates of photosynthesis, on the incorporation of 14CO2 into the photorespiratory pathway intermediates glycine and serine, and on the postillumination burst of carbon dioxide production and oxygen consumption. A combination of these results indicates that all the algae tested can photorespire, but that Glenodinium sp., Thalassiosira pseudonana, and zooxanthellae either have a photorespiratory pathway different from that proposed for freshwater algae (Tolbert, 1974), or an additional pathway for glycolate metabolism.

Energy requirement for symbiotic nitrogen fixation

Abstract: Comparing the energy required by legumes for symbiotic nitrogen fixation with that of assimilation of nitrate, Gibson concluded the costs to be about the same. About 15% of net photosynthetic production by the plant may be used in meeting its nitrogen requirements. If energy for the fixation of nitrogen symbiotically and that for the assimilation of NH4+ or NO3- from the soil solution are both provided by the chemical products of photosynthesis, then the CO2 respired in supplying that energy must contribute to the total efflux of CO2 from the plant in the dark. McCree and Thornley have discussed methods of partitioning the dark CO2 efflux into a growth (synthesis) and a maintenance component. Both nitrogen fixation and nitrogen assimilation can be expected to contribute to the CO2 flux associated with synthesis. If Gibson is correct, nodulated plants using only symbiotically fixed nitrogen should have the same growth coefficient as non-nodulated plants supplied with exogenous mineral nitrogen when grown in the same conditions. I have examined this hypothesis using a modification of the method used by McCree with Trifolium subterraneum L. cultivar Woogenellup as test material.

A Method for Studying Photosynthetic Capacities of Unicellular Algae Based on in vivo Chlorophyll Fluorescence

Abstract: The correlation between photosynthesis and DCMU-induced fluorescence increase has been studied in four species of unicellular green algae from inoculation of the cultures to the stationary growth phase. The fluorescence increase induced by DCMU was high in exponentially growing cultures but decreased when the cultures approached the stationary phase of growth. Because of the good correlation between photosynthesis and DCMU-induced fluorescence increase, the fluorescence technique is a promising method for describing changes in photosynthetic capacities of algal populations in natural waters.

The effect of sulfide on the blue-green algae of hot springs II. Yellowstone National Park.

Abstract: In the Mammoth Springs (Yellowstone National Park) waters with near neutral pH and soluble sulfide (H2S, HS−, S2−) of over 1–2 mg/liter (30–60ΜM) are characterized by substrate covers of phototrophic bacteria (Chloroflexus and aChlorobium-like unicell) above 50‡C and by a blue-green alga (Spirulina labyrinthiformis) below this temperature.Synechococcus. Mastigocladus, and other blue-green algae typical of most hot springs of western North America are excluded, apparently by sulfide. The sulfide-adaptedSpirulina photosynthesized at maximum rates at 45‡C and at approximately 300 to 700ΜEin/m2/sec of “visible” radiation. Sulfide (0.6–1.2 mM) severely poisoned photosynthesis of nonadapted populations, but those continuously exposed to over 30ΜM tolerated at least 1 mM without inhibition. A normal14C-HCO3 photoincorporation rate was sustained with 0.6–1 mM sulfide in the presence of DCMU (7ΜM) or NH2OH (0.2 mM), although both of these photosystem II inhibitors prevented photoincorporation without sulfide. Other sulfur-containing compounds (S2O32− SO32−, S2O42− thioglycolic acid cysteine) were unable to relieve DCMU inhibition. The lowering of the photoincorporation rate by preferentially irradiating photosystem I was also relieved by sulfide. The most tenable explanation of these results is that sulfide is used as a photo-reductant of CO2, at least when photosystem II is inhibited. It is suggested that in some blue-green algae photosystem II is poisoned by a low sulfide concentration, thus making these algae sulfidedependent if they are to continue photosynthesizing in a sulfide environment. Presumably a sulfidecytochrome reductase enzyme system must be synthesized for sulfide to be used as a photo-reductant.