Effects of growth irradiance on the photosynthetic action spectra of the marine dinoflagellate,Glenodinium sp.

Summary Whole cell absorption curves of the marine dinoflagellate Glenodinium sp., cultured at irradiances of 250W/cm² (low light) and 2500W/cm² (high light), were measured and their difference spectrum determined. Absorption by low light grown cells exceeded that of high light grown cells throughout the visible spectrum by a factor which ranged from 2 to 4. The difference spectrum supported the view that increased pigmentation, resulting from low light conditions, was largely due to an increase in cell content of a peridinin-chlorophyll a-protein (PCP) and an unidentified chlorophyll a component of the chloroplast membrane. Photosynthetic action spectrum measurements indicated that chlorophyll a, peridinin, and very likely chlorophyll c, were effective light-harvesting pigments for photosynthesis in both high and low light grown cultures of Glenodinium sp. Comparison of action spectra and absorption spectra suggested that low light grown cells selectively increased cellular absorption in the 480 nm to 560 nm region, and effectively utilized this spectral region for the promotion of oxygen evolution.Abbreviations PCP peridinin-chlorophyll a-protein - SIO (F.T. Haxo) Scripps Institution of Oceanography collection     

Organization of the photosynthetic units,and onset of electron transport and excitation energy distribution in greening leaves

The development and organization of the Photosynthetic units follow a step-wise assembly process. First the core complexes of the PSI and PSII units are formed, followed by their light-harvesting components; then an assembly process of these components into supramolecular structures takes place. Parallel to this, the control of excitation energy distribution between the two photosystems is established. This control is attributed to the modulation of the PSI unit effective cross section, which is possible only when LHC-I is formed and assembled into CPIa. Parallel to the formation of PSI and PSII, the electron carriers are synthesized and the electron transport chain is assembled. The number of PSII units operating per electron transport chain remains constant throughout development and equal to that of the mature chloroplast, but the number of PSI units per chain varies with PSII unit size. During development, when the rate of Chla synthesis is low, relative to the other thylakoid components, or is completely stopped, then the newly formed or preexisting LHC-I and LHC-II proteins are digested and their Chla is used for the formation of PS core complexes.     

Infinite model of connected photosynthetic units

Exciton transport in an infinite set of connected photosynthetic units is studied by using a diagrammatic expansion technique. The theory is applied to several specific models.     

Influence of lowered temperature on the resistance and functional activity of the photosynthetic apparatus of wheat plants

The dynamics of cold resistance and the activity of the photosynthetic apparatus (PSA) of wheat germs at 4°C were studied. It was shown that in the first hours of cold, a certain functional readjustment to the changed conditions takes place in the plant organism. A decrease in the activity of the PSA and cessation of the linear growth of the leaf are registered at this stage along with an increase in resistance, as well as an increase in the coefficient of non-photochemical quenching of the fluorescence of chlorophyll. In one to four days, when resistance reaches its maximum, photosynthesis and the rate of electron transport are stabilized, the chlorophyll content in the lightcollecting complex increases, and the growth recommences. The final stage of adaptation (days 4–7) is characterized not only by the steady level of resistance but also by new functional organization of the PSA, which allows the plants to endure the lowered temperature successfully.     

The action of interferon and reaferon on the functional activity of human thrombocytes

The functional activity of thrombocytes (aggregation, endo- and exocytosis) and erythrocytes (aggregation) in healthy persons given a course of interferon or reaferon treatment has been studied. The results obtained in this study indicate that these preparations produce a modulating effect on the functions of thrombocytes and erythrocytes of donors having shown abnormal functional activity of these blood cells prior to the course of treatment.     

Relationship between action spectra for chlorophyll a fluorescence and photosynthetic O2 evolution in algae

Relative excitation spectra of chlorophyll a fluorescence areshown to be very close to relative action spectra of photosystemII O₂ evolution in seven micro- and macro-algae of five phyla.The conditions under which this correspondence should hold,based on theoretical considerations, and the applications ofthis correspondence to interpretation of fluorescence excitationspectra of chlorophyll a from natural populations are discussed.The spectra presented are interpreted in relation to the light-harvestingpigments and their association with the two photosystems.     

Photosynthetic action spectra of trees: I. Comparative photosynthetic action spectra of one deciduous and four coniferous tree species as related to photorespiration and pigment complements

Comparative isoenergetic action spectra of net photosynthesis for intact, current year foliage of five tree species were determined from 400 to 710 nm by CO₂ exchange analysis. The blue (400 to 500 nm) peak of net photosynthetic activity for the green broadleaves of red alder (Alnus rubra Bong.) was reduced to a plateau for the green needle-leaves of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) and Sitka spruce (Picea sitchensis [Bong.] Carr.), a shoulder for the blue-green needles of Colorado spruce (Picea pungens Engelm.), and a reduced shoulder for the blue-white needles of Blue spruce (Picea pungens var. hoospii). These differences were attributable neither to a differential blue light stimulation of photorespiration nor to a differential presence of a nonplastid screening pigment. The conifers all had similar carotenoid-chlorophyll ratios, with approximately 50% more carotenoid relative to chlorophyll as compared to red alder. Blue light absorption and low efficiency of energy transfer by the carotenoids probably accounts for the low net photosynthetic activity of the green conifers in blue light as compared to red alder. Leaf form per se (broad versus needle) had no distinguishable influence on these results.     

Studies on the mechanism of chloride action on photosynthetic water oxidation

In this paper, we describe experiments which were designed to probe the mechanism through which Cl^? anions exert their influence on electron transport on the oxidizing side of Photosystem II (PS II). We asked whether photosynthetically active Mn was released from and reinserted into the water-splitting enzyme upon Cl^? removal and subsequent repletion, and obtained evidence suggesting that it was not. To locate the site of the Cl^?-dependent lesion, we counted the number of electrons that were still available in Cl^?-free chloroplasts for rapid reduction of P-680⁺ following a flash, and compared our results with other, previously characterized methods of inhibition. Using both delayed and prompt fluorescence as measures of the lifetime of P-680⁺, we found that Cl^?-depleted thylakoids could deliver two electrons to the oxidized PS II reaction center. This is interpreted as indicating that two oxidizing equivalents can be generated and transiently stored by PS II after Cl^? removal. Two alternative schemes which describe the functional location of electron carriers in this portion of the electron transport chain are proposed to account for our data. An experiment designed to distinguish between them is discussed. We also investigated the stability of oxidants produced by the Cl^?-depleted PS II. The apparently contradictory results obtained by prompt fluorescence and luminescence measurements are tentatively resolved by postulating the existence of two pathways through which closed reaction centers reopen, only one of which proceeds via a luminescence-producing recombination mechanism. It is suggested that deactivation of the PS-II oxidizing equivalents through both pathways is accelerated by Cl^? removal.     

Metabolic activity,the chemical composition of biomass and photosynthetic activity of Chlorella vulgaris under different light spectra in photobioreactors

Omitting the far‐red in LED lighting for bioreactors is inexplicable because it affects photosynthetic efficiency and photomorphogenetic activity. Therefore, this work compares three light sources (fluorescent—white light (WL), and LED: blue + red—BRL and blue + red + far‐red—BRFRL) for cultures of Chlorella vulgaris. Metabolic activity was determined by isothermal calorimetry. Changes in the chemical composition of biomass were examined by spectrofluorimetry and Raman spectroscopy. Maximum quantum yield of photosystem II was determined on the basis of chlorophyll a fluorescence parameters. The algae grown under BRL produced significantly more thermal energy than those cultured under BRFRL and WL. The Raman spectra of cultures showed characteristic bands for carotenoids, chlorophyll, phenolics, lipids, aliphatic carbohydrates, pectins, and disaccharides. According to the cluster analysis, the chemical composition of cultures grown under BRL and BRFRL was very similar, whereas the WL represented a distinct group. BRL and BRFRL stimulated the biosynthesis of an unidentified compound(s) with fluorescence maximum at 614 nm. At the beginning of the cultivation, photosystem II had very weak photochemical activity. Under BRFRL, ratios of Fv/Fm reached the maximum after 4 days, whereas under BRL and WL, after 6 days of cultivation. The results point to the favorable influence of the far‐red on the metabolism of microalgae.     

Excitation transfer between photosynthetic units: the 1964 experiment

We review here the background and the experiments that led to the concept of excitation energy transfer among photosystem (PS) II units. On the basis of a kinetic analysis of oxygen evolution and chlorophyll a fluorescence yield, the authors showed, in 1964, that the PS II photochemical reaction involved in the formation of oxygen is not a first-order process. We concluded that excitation energy localized in a `photosynthetic unit' including a reduced primary acceptor is transferred with a high probability to neighboring PS II units. Here, the beginnings and the original data of this topic are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

A theory of excitation transfer in photosynthetic units

A theory of the excitation kinetics in the bacteria photosynthetic unit with regard to its globular structure is presented. It assumes that the excitation transfer between globulae is carried out by means of the mechanism of incoherent excitons, at the same time considering the finite time of the excitation fixation in the reaction center. A method of local perturbations is used with a view to finding a solution to the given problem. The expressions obtained for the fluorescence decay time and its quantum yield are discussed in connection with the multiple experiments considering the cubic as well as the hexagonal probable structure of the photosynthetic unit. The analysis given shows that the period of the excitation transfer between globulae equals 10 to 100 psec and the number of the globulae is less than 35. These conclusions fall in with the initial assumption of the energy transfer between globulae by incoherent excitons. Without considering the globularity, the consistency of the theory with experimental data becomes difficult.     

The photosynthetic action spectrum of the bean plant

The photosynthetic action spectrum of the bean plant leaf, Phaseolus vulgaris L. (variety Red Kidney), has been determined with a diffraction grating illuminated by a 6500-watt xenon arc. An infrared CO₂ analyzer was used to determine the gross photosynthetic rate of the terminal leaflet of the first trifoliate leaf. The rate was measured as a function of the light intensity at steps of 12.5 nanometers which approximates the length of the leaflet used. Twenty-five curves between 400 and 700 nanometers were used to establish the action spectrum. All light curves were some linear function of the incident intensity, and all were extrapolated to zero. The action spectrum shows the following features. (a) there are two peaks (i.e., at about 670 and 630 nanometers) and a shoulder between 600 and 612 nanometers in the red region where the highest rate of photosynthesis is found. Lower peaks in descending order are found in the blue (at about 437 nanometers) and the green (at about 500 nanometers) regions. (b) There are two small minima at about 650 nanometers and between 470 and 480 nanometers, and a broad minimum is found between 540 and 530 nanometers. (c) The photosynthetic rate declines rapidly above 680 nanometers, reaching the lowest value at 700 nanometers. (d) At wave lengths below the blue maximum, the rate decreases progressively to 400 nanometers.     

Photoacoustic spectra of needles as an indicator of the activity of the photosynthetic apparatus of healthy and damaged conifers

Photoacoustic spectra were measured at chopping frequencies of the excitation light at 22 and 515 Hz in order to detect differences between needles from healthy and damaged conifers ( Abies alba Mill, and Picea abies Karst.) with respect to pigment distribution and possibly also to photosynthetic activity. Fully green needles of healthy trees exhibit photoacoustic spectra at 22 Hz with a maximum in the red absorption region of the chlorophyll. This maximum is lost with increasing damage to needles and chlorophyll breakdown. The photoacoustic spectra at 22 Hz of the damaged needles therefore are characterized by a higher signal in the blue-light region as compared to that in the red-light region. This can be quantified by forming the ratio of the photoacoustic signals at 675 and 475 nm (ratio PA 675/475). The needles of the damaged trees possess a lower photosynthetic activity, as seen from the CO₂ fixation rate and the variable fluorescence (Rfd-values). It is assumed that the changes in the PA-spectra of the needles from damaged trees are the result of this decline of the photosynthetic apparatus and its function. In contrast to the PA-spectrum at 22 Hz the PA-spectra at 515 Hz, where the PA-signals primarily emanate from the epidermal layer, exhibit a different shape with a maximum near 550 nm. In the needles from the damaged trees the PA-signals are higher, particularly in this maximum range of the spectrum, than those of fully green needles from healthy trees.     

The modulatory action of superlow doses of mediators on the functional activity of the neuronal membrane]

It was shown that acetylcholine and gamma-aminobutyric acid at extremely low concentrations, which do not activate receptor-binding ionic channels, modulate the activity of NA-K-pump and Na:Ca exchange, the intracellular level of cAMP and chemosensitivity of the neuronal membrane. These data provide a new evidence in support for Koshtoiants's enzymochemical hypothesis in which synaptic transmitters are considered to be metabolic modulators for postsynaptic neurones.     

The effect of relaxed functional constraints on the photosynthetic gene rbcL in photosynthetic and nonphotosynthetic parasitic plants

The photosynthetic gene rbcL has been lost or dramatically altered in some lineages of nonphotosynthetic parasitic plants, but the dynamics of these events following loss of photosynthesis and whether rbcL has sustained functionally significant changes in photosynthetic parasitic plants are unknown. To assess the changes to rbcL associated with the loss of functional constraints for photosynthesis, nucleotide sequences from nonparasitic and parasitic plants of Scrophulariales were used for phylogeny reconstruction and character analysis. Plants in this group display a broad range of parasitic abilities, from photosynthetic ("hemiparasites") to nonphotosynthetic ("holoparasites"). With the exception of Conopholis (Orobanchaceae), the rbcL locus is present in all parasitic plants of Scrophulariales examined. Several holoparasitic genera included in this study, including Boschniakia, Epifagus, Orobanche, and Hyobanche, have rbcL pseudogenes. However, the holoparasites Alectra orobanchoides, Harveya capensis, Harveya purpurea, Lathraea clandestina, Orobanche corymbosa, O. fasciculata, and Striga gesnerioides have intact open reading frames (ORFs) for the rbcL gene. Phylogenetic hypotheses based on rbcL are largely in agreement with those based on sequences of the nonphotosynthetic genes rps2 and matK and show a single origin of parasitism, and loss of photosynthesis and pseudogene formation have been independently derived several times in Scrophulariales. The mutations in rbcL in nonparasitic and hemiparasitic plants would result in largely conservative amino acid substitutions, supporting the hypothesis that functional proteins can experience only a limited range of changes, even in minimally photosynthetic plants. In contrast, ORFs in some holoparasites had many previously unobserved missense substitutions at functionally important amino acid residues, suggesting that rbcL genes in these plants have evolved under relaxed or altered functional constraints.      

Artificial increase of the light-harvesting ability of photosynthetic units in isolated chloroplasts

A synthetic fluorochromous lipid, rhodaminyl triglyceride (rhodaminyl TG), was intercalated into isolated thylakoid membranes of chloroplasts up to 30 molecules per 100 molecules of chlorophyll. As a result of fluorochrome presence, an absorption band appeared in a yellow-green spectrum region, its intensity being comparable with the red and blue chlorophyll bands. The energy absorbed by rhodaminyl TG was transferred through chlorophyll to the reaction centers of photosystems I and II, inducing an additional electron flow of about 30%. Therefore the exogenous fluorochrome dissolved in lipid matrix functions as an accessory pigment which significantly modifies the spectral sensitivity of the photosynthetic process. The energy transfer from rhodaminyl TG to chlorophyll occurs by mechanism of the inductive resonance type.Abbreviations rhodaminyl TG rhodaminyl triglyceride (rac-1,2-dioleoyl-3[11(3-rhodaminyl)amino-undelanoyl]glycerol) - Me₂SO dimethylsulfoxide - PS photosystem - PPC pigment-protein complex - F₀, F_m initial and maximal levels of chlorophyll fluorescence     

Organization of intracytoplasmic membranes in a novel thermophilic purple photosynthetic bacterium as revealed by absorption, circular dichroism and emission spectra

The chromatophore of a novel thermophilic purple photosynthetic bacterium, Chromatium tepidum, had light-harvesting BChl proteins which gave absorption maxima at 917, 855 and 800 nm at 20°C. These antenna complexes were found to have BChl of the a type [4]. This is, therefore, the first example of a BChl a antenna complex which shows a long-wavelength absorption up to 917 nm. Treatment by Triton X-100 and successive sodium dodecyl sulfate polyacrylamide gel electrophoresis separated these antenna complexes into two groups. One of them has one antenna component which absorbs around 917 nm (B917). The other contains at least an antennae which absorb maximally at 800 and 855 nm (B800–855). The temperature-dependent changes of absorption, circular dichroism and emission spectra were reversible up to 70°C in the intact chromatophore and in the isolated B800–855 complex. On the contrary, the isolated complex B917 lost its absorption irreversibly over the temperature of 50°C. These results suggest a membrane structure which is essential for the thermostability of chromatophores from C. tepidum.     

Toxicity assessment of common organic solvents using a biosensor based on algal photosynthetic activity measurement

The acute toxicities of common organic solvents (e.g., methanol, ethanol, isopropanol, acetone, acetonitrile, and dimethylformamide) were evaluated using a biosensor based on microalgal photosynthesis measurement. The biosensor was air-tight, with no headspace, preventing volatile organic toxicants from escaping into the environment as well as partitioning from the aqueous phase into the headspace until equilibrium was reached. Both the incubating and exposure times were set at 10 min. It was observed that only 2 h was needed to obtain complete dose-related inhibition of photosynthetic activity. The results showed that all the tested organic solvents inhibited algal photosynthesis with EC₅₀ ranging between 589 and 2,570 mM. The inhibition of these solvents was in the order: isopropanol > acetone > acetonitrile > ethanol > dimethylformamide > methanol. The quantitative structure-activity relationship (QSAR) between toxicity data and partition coefficient of the examined compounds could be modeled as follows: ${\text{log}}_{{10}} {\text{EC}}_{{50}} \;{\left( {\mu {\text{M}}} \right)} = - 0.6428\;{\text{log}}\;P + 5.76\;{\left( {{\text{R}}^{2} \approx 0.88} \right)}The acute toxicities of common organic solvents (e.g., methanol, ethanol, isopropanol, acetone, acetonitrile, and dimethylformamide) were evaluated using a biosensor based on microalgal photosynthesis measurement. The biosensor was air-tight, with no headspace, preventing volatile organic toxicants from escaping into the environment as well as partitioning from the aqueous phase into the headspace until equilibrium was reached. Both the incubating and exposure times were set at 10 min. It was observed that only 2 h was needed to obtain complete dose-related inhibition of photosynthetic activity. The results showed that all the tested organic solvents inhibited algal photosynthesis with EC₅₀ ranging between 589 and 2,570 mM. The inhibition of these solvents was in the order: isopropanol > acetone > acetonitrile > ethanol > dimethylformamide > methanol. The quantitative structure-activity relationship (QSAR) between toxicity data and partition coefficient of the examined compounds could be modeled as follows: \textlog₁₀ \textEC₅₀   ( m\textM ) = - 0.6428  \textlog  P + 5.76  ( \textR² ? 0.88 ){\text{log}}_{{10}} {\text{EC}}_{{50}} \;{\left( {\mu {\text{M}}} \right)} = - 0.6428\;{\text{log}}\;P + 5.76\;{\left( {{\text{R}}^{2} \approx 0.88} \right)}. This indicates that the photosynthetic activity of the microalga Pseudokirchneriella subcapitata is highly dependent on the hydrophobicity of these commonly used organic solvents.