Showing papers on "Photosynthesis published in 1978"

Photorespiratory nitrogen cycle

Abstract: MOST temperate plants form phosphoglyceric acid as the first stable product of photosynthesis. These plants also photo-respire, that is, during CO2 fixation they simultaneously release CO2 to the atmosphere from the oxidation of an intermediate of the photosynthetic process1,2. The reaction below, which takes place in the mitochondria3,4, is chiefly responsible for this CO2 release.

Carotenoids in photosynthesis

Abstract: Carotenoids are usually considered to perform two major functions in photosynthesis. They serve as accessory light harvesting pigments, extending the range of wavelengths over which light can drive photosynthesis, and they act to protect the chlorophyllous pigments from the harmful photodestructive reaction which occurs in the presence of oxygen. Drawing upon recent work with photosynthetic bacteria, evidence is presented as to how the carotenoids are organized within both portions of the photosynthetic unit (the light harvesting antenna and the reaction centre) and how they discharge both their functions. The accessory pigment role is a singlet-singlet energy transfer from the carotenoid to the bacteriochlorophyll, while the protective role is a triplet-triplet energy transfer from the bacteriochlorophyll to the carotenoid.

Photosynthetic Acclimation to Temperature in the Desert Shrub, Larrea divaricata: II. Light-harvesting Efficiency and Electron Transport

Abstract: The response of photosynthetic electron transport and light-harvesting efficiency to high temperatures was studied in the desert shrub Larrea divaricata Cav. Plants were grown at day/night temperatures of 20/15, 32/25, or 45/33 C in rough approximation of natural seasonal temperature variations. The process of acclimation to high temperatures involves an enhancement of the stability of the interactions between the light-harvesting pigments and the photosystem reaction centers. As temperature is increased, the heat-induced dissociation of these complexes results in a decrease in the quantum yield of electron transport at limiting light intensity, followed by a loss of electron transport activity at rate-saturating light intensity. The decreased quantum yield can be attributed to a block of excitation energy transfer from chlorophyll b to chlorophyll a, and changes in the distribution of the excitation energy between photosystems II and I. The block of excitation energy transfer is characterized by a loss of the effectiveness of 480 nm light (absorbed primarily by chlorophyll b) to drive protochemical processes, as well as fluorescence emission by chlorophyll b.

Photosynthesis by Isolated Protoplasts, Protoplast Extracts, and Chloroplasts of Wheat: Influence of Orthophosphate, Pyrophosphate, and Adenylates

Abstract: Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat ( Triticum aestivum ) have rates of photosynthesis as measured by light-dependent O 2 evolution of about 100 to 150 micromoles of O 2 per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO 3 with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O 2 per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset. Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5′-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5′-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP. Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO 3 and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed.

Effect of temperature on blue-green algae (cyanobacteria) in lake mendota.

Abstract: The temperature optimum for photosynthesis of natural populations of blue-green algae (cyanobacteria) from Lake Mendota was determined during the period of June to November 1976. In the spring, when temperatures ranged from 0 to 20°C, there were insignificant amounts of blue-green algae in the lake (less than 1% of the biomass). During the summer and fall, when the dominant phytoplankton was blue-green algae, the optimum temperature for photosynthesis was usually between 20 and 30°C, whereas the environmental temperatures during this period ranged from 24°C in August to 12°C in November. In general, the optimum temperature for photosynthesis was higher than the environmental temperature. More importantly, significant photosynthesis also occurred at low temperature in these samples, which suggests that the low temperature alone is not responsible for the absence of blue-green algae in Lake Mendota during the spring. Temperature optima for growth and photosynthesis of laboratory cultures of the three dominant blue-green algae in Lake Mendota were determined. The responses of the two parameters to changes in temperature were similar; thus, photosynthesis appears to be a valid index of growth. However, there was little photosynthesis by laboratory cultures at low temperatures, in contrast to the natural samples. Evidence for an interaction between temperature and low light intensities in their effect on photosynthesis of natural samples is presented.

Photosynthetic Acclimation to Temperature in the Desert Shrub, Larrea divaricata: I. Carbon Dioxide Exchange Characteristics of Intact Leaves.

Abstract: Larrea divaricata, a desert evergreen shrub, has a remarkable ability to adjust its photosynthetic temperature response characteristics to changing temperature conditions. In its native habitat on the floor of Death Valley, California, plants of this C(3) species when provided with adequate water are able to maintain a relatively high and constant photosynthetic activity throughout the year even though the mean daily maximum temperature varies by nearly 30 C from winter to summer. The temperature dependence of light-saturated net photosynthesis varies in concert with these seasonal temperature changes whereas the photosynthetic rate at the respective optimum temperatures shows little change.Experiments on plants of the same age, grown at day/night temperatures of 20/15, 35/25, and 45/33 C with the same conditions of day length and other environmental factors, showed a similar photosynthetic acclimation response as observed in nature. An analysis was made of a number of factors that potentially can contribute to the observed changes in the temperature dependence of net CO(2) uptake at normal CO(2) and O(2) levels. These included stomatal conductance, respiration, O(2) inhibition of photosynthesis, and nonstomatal limitations of CO(2) diffusive transport. None of these factors, separately or taken together, can account for the observed acclimation responses. Measurements under high saturating CO(2) concentrations provide additional evidence that the observed adaptive responses are primarily the result of changes in intrinsic characteristics of the photosynthetic machinery at the cellular or subcellular levels. Two apparently separate effects of the growth temperature regime can be distinguished: one involves an increased capacity for photosynthesis at low, rate-limiting temperatures with decreased growth temperature, and the other an increased thermal stability of key components of the photosynthetic apparatus with increased growth temperature.

Effects of light intensity on photosynthesis and dark respiration in six species of marine phytoplankton

Abstract: Using an oxygen polarographic electrode, the shapes of photosynthetic curves and the effects of light on dark respiration in 6 species of marine phytoplankton wer examined. The species used were Skeletonema costatum, Ditylum brightwellii, Cyclotella nana (Thalassiosira pseudonana) (all Bacillariophyceae), Dunaliella tertiolecta (Chlorophyceae), Isochrysis galbana (Haptophyceae), and Gonyaulax tamarensis (Dinophyceae). A hysteresis was observed in all species examined with respect to increasing and decreasing light. Compensation light intensities varied by over 4 orders of magnitude, suggesting that the 1% light depth is an ambiguous measure of the euphotic zone. The data suggest that dark respiration accounts for ca. 25% of gross photosynthesis, but is species-dependent. In addition, respiration versus cell size does not describe an inverse exponential function over the size scales examined.

Effects of Sink Removal on Photosynthesis and Senescence in Leaves of Soybean (Glycine max L.) Plants

Abstract: Photosynthetic rate, ribulose 1,5-bisphosphate carboxylase activity, specific leaf weight, and leaf concentrations of carbohydrates, proteins, chlorophyll, and inorganic phosphate were determined periodically from midbloom until maturity in leaves of soybean plants ( Glycine max L., var. Hodgson) from which reproductive and vegetative sinks had been removed 32 hours before measurement, or continuously since midbloom. Leaf photosynthesis, measured in the top of the canopy, was partially inhibited by both sink removal treatments. This inhibition was of constant magnitude from midbloom until maturity. Leaf photosynthesis in the top of the canopy declined from midbloom until maturity in the control as well as in the desinked plants. The decline in photosynthesis was gradual at first, but later became more abrupt. The photosynthetic decline was equally evident in the yellowing leaves of control plants and in the dark green leaves of the continuously desinked plants. Neither the inhibition of photosynthesis by sink removal nor the decline in photosynthetic rate with time was clearly related to any of the measured traits.

Chlorophyll function in the photosynthetic reaction center.

Abstract: The concern in this review is exclusively with the photoreaction centers associated with PS I activity in green plants and with the reaction centers of purple (nonsulfur) photosynthetic bacteria. For the most part the discussion is based on physical chemical studies carried out over the past 15 years on chlorophyll in defined in vitro systems, which have provided new insights on the molecular level into some fundamental properties of chlorophyll that are important and perhaps decisive to the understanding of the structure and function of photoreaction-center chlorophylls.

The Effect of Cadmium on Net Photosynthesis, Transpiration, and Dark Respiration of Excised Silver Maple Leaves

Abstract: Excised leaves of silver maple (Acer saccharinum L.) exposed to 0, 0.045, 0.090, or 0.180 mM Cd24 exhibited reduced net photosynthesis and transpiration, and increased dark respiration. Rates of net photosynthesis and transpiration diminished with time and were strongly correlated with solution concentration and tissue content of Cd24, Net photosynthesis and transpiration were reduced to 18 and 21%, respectively, of the untreated controls after 64 h. Dark respiration increased as much as 193% of the untreated controls but was poorly correlated with solution concentration or tissue content of Cd24, Diffusive resistances of leaves to carbon dioxide and water vapor transfer increased with both increasing Cd24 concentration and time. These findings are discussed in relation to stomatal function.

Agronomic and physiological responses of soybean and sorghum crops to water deficits. III. Components of leaf water potential, leaf conductance, 14CO2 photosynthesis, and adaptation to water deficits

Abstract: Concurrent measurements of leaf water potential, leaf osmotic potential, leaf relative water content, quantum flux density, leaf conductance, 14CO2 photosynthesis, soluble and insoluble sugars, starch and potassium concentrations were made diurnally on six occasions between flowering and maturity on upper leaves of irrigated and rainfed crops of soybean (cvv. Ruse and Bragg) and a rainfed crop of sorghum (cv. TX 610). With adequate soil water, sorghum had lower values of leaf conductance than did soybeans at high light and yet had higher rates of photosynthesis. Stage of plant development had no effect on either leaf conductance or photosynthesis of the youngest fully expanded leaves of both sorghum and soybean, but starch accumulation in the leaf over the day was less at grain-filling than at flowering in the soybean. Starch and sugar levels in the leaf had no apparent effect on photosynthesis. The daily minimum leaf water potential decreased in Ruse soybean from - 1.5 to -2.7 MPa as soil water was depleted. Late in the drying cycle, the daily minimum leaf water potential was higher in Bragg than in Ruse. In both cultivars, stomatal closure and decrease in 14CO2 photosynthesis commenced at leaf water potentials below - 1.5 MPa. Thus, the effect of water deficits on leaf conductance and photosynthesis occurred later in the drying cycle in Bragg than Ruse. As photosynthesis decreased with the depletion of soil water, starch accumulation in leaves of both cultivars of soybean decreased; changes in soluble and insoluble sugars and in potassium were small. The relationships among leaf water potential, osmotic potential, turgor potential, and leaf relative water content did not change with season or soil water depletion. Bragg and Ruse soybeans showed a similar response and both approached zero turgor at the same relative water content (82-83 %) and the same leaf water potential (- 1.5 to - 1.7 MPa). No evidence ofr osmotic adjustment was found in either soybean cultivar.

Adaptation of the Photosynthetic Apparatus of Scenedesmus obliquus to Strong and Weak Light Conditions

Abstract: Homocontinuous cultures of the unicellular green alga Scenedesmus obliquus were grown under strong (28 W/m2∼28,000 lux) and weak (5 W/m2∼5000 lux) light conditions to simulate the conditions of ‘sun’ and ‘shade’ plants. As in higher plants the cells adapted to strong light had less chlorophyll but demonstrated a higher photosynthetic capacity and a higher respiration rate, so that their compensation point was reached at three times higher energy than in the cells grown under low light intensities. The CO2 fixation rate and the RuDP carboxylase activity under saturating light intensities were both higher in the cells grown in strong light. In spite of the differences in the pigment content and in the light saturated photosynthetic capacities for both cultures, the quantum yields of photosynthetic oxygen evolution were equal. As documented for some species of higher plants Scenedesmus is not genetically determined to be either a ‘sun’ or ‘shade’ organism but can adapt its photosynthetic apparatus to the different light intensities.

Delayed Fluorescence in Photosynthesis

Abstract: 3.2 Rate Constant, Exciton Yield, and Emission Yield . . 3.3 Delayed Fluorescence from "Closed" Reaction Centers .. 4. SECONDARY ELECTRON TRANSPORT IN PHOTOSYSTEM II .. 4.1 S states .. 4.2 Decay Kinetics . 4.3 Temperature Dependence . Emission at low temperatures .

Products of photosynthesis in natural populations of marine phytoplankton from the gulf of maine.

Abstract: We have measured the photosynthetic assimilation of 14C-carbon dioxide into (1) ethanol-soluble, (2) hot-trichloroacetic acid (TCA)-soluble (polysaccharide), and (3) protein fractions of natural populations of marine phytoplankton. Diurnal studies showed a continuing incorporation of carbon-14 into the protein fraction during hours of darkness. This was accompanied by a concomitant decrease in the proportion assimilated into polysaccharide. When incorporation was measured under constant experimental conditions, the pattern of photosynthesis did not vary from one time of day to another. At one station approximately 12 km south of Boothbay Harbor, the proportion of carbon entering protein showed marked seasonal changes. During the winter, approximately 10 to 20% of the fixed carbon was incorporated into protein. During the summer the value increased to 22 to 35%. Between these times, a transient high value of 37 to 47% of the fixed carbon entering protein coincided with the spring bloom. The increases in proportion incorporated into protein were largely paralleled by equivalent decreases in the polysaccharide fraction. The proportion of carbon incorporated into protein during photosynthesis also increased markedly at reduced light intensities. This increase occurred both when populations were incubated in neutral-density filters and when incubated at increasing depths in the photic zone. There was little consistent and significant difference between the neutral-density filters and depth in the water column, suggesting a minimal role for light quality. The extent of the increased relative rate of protein synthesis at the lower light intensities depended on the nutritional state of the phytoplankton. For example, summer populations from water containing low concentrations of inorganic nutrients responded less dramatically to reduced light intensities than did populations from nutrient-rich waters.

Chlorophyll fluorescence induction: an indicator of photosynthetic activity in marine algae undergoing desiccation

Abstract: Algae of higher intertidal regions tend to be tolerant of extended periods of desiccation, while many lower tidal or subtidal species do not withstand even mild water loss. (Tidal regions can be characterized as high (regularly immersed at high tide and exposed at low tide), low (emergence only during minus tides (lower than mean low tide)), or subtidal (never exposed at low tide and extending to the maximum depth at which net photosynthesis can occur).) The ecological necessity for tolerance in frequently emerged species is obvious, but the physiological basisof it is not well understood. Changes of photosynthetic partial reactions upon desiccation and rehydl-ation of tolerant and sensitive algae were studied by measurements of chlorophyll fluorescence induction kinetics (Kautsky effect). With progressive decrease in water content the gradual disappearance of the characteristic fluorescence transients was observed in both tolerant and sensitive species. The water content ranges where typical changes occurred were species dependent. Rehydration in tolerant plants resulted in rapid recovery from severe desiccation; there was no such recovery in sensitive plants when water content was decreased below a critical value. Analysis of the fluorescence changes upon desiccation and rehydration suggests: (I) electron transport between photosystem 11 and photosystem I. 21s well as H20 splitting are the partial reactions sensitive to desiccation; (2) in the resistant Porpl~yrn sn~ljlin~~e~lsis , intersystem electron transport is blocked at around 25% water content; (3) further desiccation leads to loss of water-splitting activity and eventually to the complete loss of variable fluorescence photosystem 11 reaction centers; and (4) on rehydration intersystem electron transport begins almost immediately while recovery of H20 splitting requires several minutes.

A comparison of photosynthetic characteristics of encelia species possessing glabrous and pubescent leaves.

Abstract: Measurements of the dependence of photosynthesis on light, CO2, and temperature are reported for two species of Encelia (Compositae) which differ in leaf pubescence and in geographical distribution. Encelia californica is glabrous and occurs in relatively mild, but arid habitats and Encelia farinosa is heavily pubescent and occurs in hot, arid habitats. Both species possess the C3 photosynthetic pathway. Under high irradiances and normal atmospheric conditions the two species have high photosynthetic rates, exceeding 3 nanomoles of CO2 per square centimeter per second (48 milligrams of CO2 per square decimeter per hour) and complete light saturation does not occur by full noon sunlight. The high photosynthetic capacity is related to a high efficiency of utilization of intercellular CO2 combined with high stomatal conductance. Leaf estimates of total soluble protein and fraction I protein are higher in these species than in most plants, although the proportion of fraction I protein is not higher. Both E. californica and E. farinosa attain a maximum rate of photosynthesis between 25 and 30 C, despite the fact that the two species grow in very different thermal habitats. Neither E. californica nor E. farinosa shows significant acclimation in the temperature dependence of photosynthesis when grown under different temperature regimes. The presence of leaf hairs which reduce leaf absorptance and consequently leaf temperature plays an important part in the ability of E. farinosa to survive in its native high temperature environment. When the effects of pubescence are taken into account, there are few if any significant differences in the photosynthetic characteristics of the two species.

Regulation of chloroplast development by red and blue light

Abstract: There are specific differences between red and blue light greening of etiolated seedlings of Hordevm vulgare L. Blue light results in a different prenyl lipid composition of chloroplast as compared to red light of equal quanta density. This is documented by a much higher prenylquinone content, higher chlorophyll a/b ratios, and lower values for the ratio xanthophylls to carotenes (x/c). The photosynthetic activity of “blue light” chloroplasts (Hill reaction) is higher than that of “red light” chloroplasts. These differences in prenylquinone composition and Hill-activity are associated with a different ultrastructure of chloroplasts. “Red light” chloroplasts exhibit a much higher grana content than “blue light” chloroplasts. The difference in thylakoid composition, photosynthetic activity and chloroplast structure found between blue and red light greening are similar to those found between sun and shade leaves and those between plants grown under high and low light intensities.

Fixation of 18O2 during Photorespiration: Kinetic and Steady-State Studies of the Photorespiratory Carbon Oxidation Cycle with Intact Leaves and Isolated Chloroplasts of C3 Plants 1

Abstract: Mass spectrometric techniques were used to trace the incorporation of [ 18 O]oxygen into metabolites of the photorespiratory pathway. Glycolate, glycine, and serine extracted from leaves of the C 3 plants, Spinacia oleracea L., Atriplex hastata, and Helianthus annuus which had been exposed to [ 18 O]oxygen at the CO 2 compensation point were heavily labeled with 18 O. In each case one, and only one of the carboxyl oxygens was labeled. The abundance of 18 O in this oxygen of glycolate reached 50 to 70% of that of the oxygen provided after only 5 to 10 seconds exposure to [ 18 O]oxygen. Glycine and serine attained the same final enrichment after 40 and 180 seconds, respectively. This confirms that glycine and serine are synthesized from glycolate. The labeling of photorespiratory intermediates in intact leaves reached a mean of 59% of that of the oxygen provided in the feedings. This indicates that at least 59% of the glycolate photorespired is synthesized with the fixation of molecular oxygen. This estimate is certainly conservative owing to the dilution of labeled oxygen at the site of glycolate synthesis by photosynthetic oxygen. We examined the yield of 18 O in glycolate synthesized in vitro by isolated intact spinach chloroplasts in a system which permitted direct sampling of the isotopic composition of the oxygen at the site of synthesis. The isotopic enrichment of glycolate from such experiments was 90 to 95% of that of the oxygen present during the incubation. The carboxyl oxygens of 3-phosphoglycerate also became labeled with 18 O in 20- and 40-minute feedings with [ 18 O]oxygen to intact leaves at the CO 2 compensation point. Control experiments indicated that this label was probably due to direct synthesis of 3-phosphoglycerate from glycolate during photorespiration. The mean enrichment of 3-phosphoglycerate was 14 ± 4% of that of glycine or serine, its precursors of the photorespiratory pathway, in 10 separate feeding experiments. It is argued that this constant dilution of label indicates a constant stoichiometric balance between photorespiratory and photosynthetic sources of 3-phosphoglycerate at the CO 2 compensation point. Oxygen uptake sufficient to account for about half of the rate of 18 O fixation into glycine in the intact leaves was observed with intact spinach chloroplasts. Oxygen uptake and production by intact leaves at the CO 2 compensation point indicate about 1.9 oxygen exchanged per glycolate photorespired. The fixation of molecular oxygen into glycolate plus the peroxisomal oxidation of glycolate to glyoxylate and the mitochondrial conversion of glycine to serine can account for up to 1.75 oxygen taken up per glycolate. These studies provide new evidence which supports the current formulation of the pathway of photorespiration and its relation to photosynthetic metabolism. The experiments described also suggest new approaches using stable isotope techniques to study the rate of photorespiration and the balance between photorespiration and photosynthesis in vivo.

Regulation of nitrate reduction by light, ATP and mitochondrial respiration in wheat leaves

Abstract: ASSIMILATION of nitrate in leaves is closely linked with photosynthesis1,2 because ammonia, the end product of the former process, is incorporated into amino acids by means of carbon skeletons derived from the assimilation of CO2. Canvin and Atkins3,4 have shown that the reduction of nitrate to nitrite in leaves of barley is dependent on light and ceases when the light is extinguished. On the other hand, in the in vivo5 method for assay of nitrate reductase, nitrate is reduced to nitrite by leaf disks even in the dark. As Canvin and Atkins3,4 pointed out, the in vivo method is not a true reflection of what happens in plants in physiological conditions. A regulatory mechanism must exist in leaves, which shuts off nitrate reduction immediately when light is extinguished, so that the accumulation of toxic amounts of nitrite, which can only be reduced by photosynthetic reactions6, is avoided. We now propose that this regulation functions through mitochondrial respiration, which operates in the dark, but is inhibited in light, because of the increased cytoplasmic adenylate charge due to photosynthesis.