Light Saturation Curves Research Articles

Ozone-induced changes in CO 2 assimilation, O 2 evolution and chlorophyll a fluorescence transients in barley

Spring barley ( Hordeum vulgare cv. Klaxon) plants, 9 days old, were exposed to 0.05, 0.10 or 0.15 μl litre −1 ozone (O 3) for 12 days. Fumigation was administered for 7 h between 9.00 h and 16.00 h each day. Using conventional IRGA equipment, the carbon dioxide exchange rate (CER) was shown to decrease with increasing concentration of O 3 during the exposure period, falling to 60% of the control value at the highest O 3 concentration. Transpiration rates and stomatal conductance showed similar trends. Light saturation curves, obtained using a leaf disc oxygen electrode, demonstrated that O 3-treated leaves had lower apparent quantum yields (QY) and generally lower rates of O 2 evolution at saturating light and CO 2 levels. Oscillations in chlorophyll a fluorescence, normally observed in control plants, could not be detected after O 3 treatment and could only be restored to some extent by feeding the phosphate sequestering agent d-mannose to the leaves.

Photosynthesis and transpiration of healthy and diseased spruce trees in the course of three vegetation periods

CO2- and H2O-gas exchange of 20- to 25-year-old spruce trees from a plantation in the Hunsruck mountains were investigated over a period of 3 years. All measurements were made as pair comparisons, i.e., in each case the gas exchange of a damaged tree and of a relatively healthy tree in its immediate vicinity was measured simultaneously. A second plantation in the Westerwald mountains consisted of 18-year-old apparently healthy spruce trees. Pair comparison at this location meant comparison of two healthylooking trees. The investigations at both locations included diurnal course measurements of photosynthesis and transpiration, and light saturation curves and CO2-saturation curves of photosynthesis. The reduced photosynthesis parameters of the phenotypically damaged trees at the Hunsruck location indicates massive damage to the photosynthetic apparatus. Measurements of H2O-gas exchange showed that there are disturbances in stomatal regulation of the needles of damaged trees. As a result, the water use efficiency of these needles proved to be significantly lower. In addition, apparent photorespiration of the damaged trees was decreased, whereas their light- and CO2-compensation points and their dark respiration were increased. In contrast to the Hunsruck plantation, no such effects were detectable when the healthy-looking Westerwald trees were subjected to pair comparison of gas exchange. Reduced photosynthetic capacity and disturbances of the stomatal regulation of the phenotypically damaged Hunsruck trees may be due to damage in the cellular membranes. Furthermore, a comparison of three growing seasons led to the conclusion that the gas exchange of spruce trees in their natural habitat is markedly influenced by climatic conditions.

Heterogeneity among photosystem II α. Isolation of thylakoid membrane vesicles with different functional antennae size of photosystem II α

The functional antenna size of different chloroplast membrane vesicles was determined from ligh-saturation curves of the oxygen evolution using paraphenylbenzoquinone as acceptor. Thylakoids showed a biphasic light-saturation curve indicative of the presence of at least two types of PS II unit, PS II α and PS II β. Inside-out thylakoids were isolated by press treatment and phase partition. These vesicles, which contain only PS II α, were then further fragmented and separated into different classes of vesicles by a sonication-phase partition procedure (Svensson, P. and Albertsson, P.-Å. (1987) in Progress in Photosynthesis Research (Biggins, J., ed.), Vol. II, pp. 281–284, Martinus Nijhoff, Dordrecht). Three fractions enriched in PS II α were obtained; these differ in the antenna size of PS II α by up to 20%. It is suggested that the size of the light-harvesting complex of PS II α from different PS II α units changes in increments of about 25–50 chlorophyll molecules depending on localization of the units in the grana or different parts of the leaf.

Interaction between Sucrose Synthesis and CO 2 Fixation III. Response of biphasic induction kinetics and oscillations to manipulation of the relation between electron transport, calvin cycle, and sucrose synthesis

This article investigates the influence of sucrose synthesis on the light response curve of photosynthesis, on induction kinetics and on photosynthetic oscillations. The occurrence of oscillations and analysis of chlorophyll fluorescence quenching at saturating light intensities shows there is surplus electron transport capacity which cannot be used due to a limitation in carbon metabolism. This limitation is increased when high fructose 2,6-bisphosphate and low sucrose phosphate synthase activity are restricting the rate of sucrose synthesis. After feeding phosphate, raised levels of metabolites allowed higher rates of sucrose synthesis even though sucrose phosphate synthase deactivated and fructose-2,6-bisphosphate rose. The maximum rate of photosynthesis is increased, the light intensities needed to saturate photosynthesis are increased and the transients and oscillations become less marked. Feeding mannose to inhibit sucrose synthesis has the opposite effect on all these parameters. Chemicals which inhibit electron transport (dichlorophenylmethyl urea), energisation and stromal alkalinisation (dinitrophenol, acetate) and ribulose-1,5-bisphosphate carboxylase (cyanide) abolished the oscillations without reducing the maximum steady state rate of photosynthesis. They also, with the exception of cyanide, decreased the initial slope of the light saturation curve. It is discussed how changes in the induction kinetics, in oscillations and in the response of the light response curve can be combined with metabolite analysis to provide a way of screening for chemicals or conditions which modify sucrose synthesis. As an example, it is shown that lithium inhibits photosynthesis via a selective restriction of sucrose synthesis, probably acting by inhibiting the cytosolic fructose-1,6-bisphosphatase.

Energetic Efficiency of Hydrogen Photoevolution by Algal Water Splitting

Absolute thermodynamic efficiencies of conversion of light energy into chemical-free energy of molecular hydrogen by intact microalgae have been measured with an original physical measuring technique using a tin-oxide semiconducting gas sensor. Thin films of microalgae comprising of 5 to 20 cellular monolayers have been entrapped on filter paper, thereby constraining them in a well-defined circular geometry. Based on absolute light absorption of visible polychromatic illumination in the low-intensity region of the light saturation curve, conversion efficiencies of 6 to 24% have been obtained. These values are the highest ever measured for hydrogen evolution by green algae.

Hydrogen photoproduction by algae and higher plants: Optimal conditions for polarographic determination

Photosynthetic H2 production capacity has been studied using a H2 sensitive electrode in green and blue-green algae, higher plant cells and chloroplasts and photosynthetic bacteria. Among the cell types tried,Anacystis showed the maximum rate of H2 production. All the cell types require either an electron acceptor or a reductant (sodium dithionite) for H2 production. In the presence of an electron acceptor or reductant H2 production was observed even in unadapted cells. Cultures ofAnacystis grown for a maximum period of 70 days showed a high rate of H2 production up to 40 days. The light saturation curves and pH optima for H2 production were similar to that of O2 evolution in the cell types studied.

Effects of high irradiances on photosynthesis, growth and crassulacean acid metabolism in the epiphyteKalanchoö uniflora.

Kalanchoë uniflora was grown in the glasshouse with and without shading. Chlorophyll content, area/FW ratio and specific leaf area were higher in leaves of shaded as compared to unshaded plants. Light saturation curves and continuous gas exchange measurements showed that the apparent quantum yield and the light-saturated photosynthetic rate were higher in shaded plants. Shaded plants had lower "mesophyll resistances" than unshaded plants, indicating that the different photosynthetic capacities reflected different contents of ribulose biphosphate carboxylase-oxygenase. Highlight treatment of plants grown in the shade resulted in a decreased photosynthetic efficiency, showing that these plants were sensitive to photoinhibition. However, dry matter production was higher in unshaded than in shaded plants. Obviously the difference in irradiance between the two growth regimes did more than offset the differences in photosynthetic efficiency. Applying additional nutrients did not alter the effects of high PFDs. The results are discussed in respect to photosynthetic performence and plant distribution in the epiphytic habitat.

Control of the Photosynthetic Apparatus of Acetabularia mediterranea by Blue Light

During growth, Acetabularia mediterranea requires the action of blue light to maintain high rates of photosynthesis. In the present study, blue light-dependent alterations of the photosynthetic apparatus, which can be detected by analysis of light-saturation curves and by measurements of partial reactions of the photosynthetic electron transport chain, are described. Light-saturation curves of photosynthesis in vivo were measured with a new closed oxygen electrode system after culture of Acetabularia in continuous red or blue light. These curves were compared to those of 2,6-dichlorophenol-indophenol reduction by isolated chloroplast membranes. The analysis lead to the following statements: (a) only one reaction limits electron transport rates in vitro (dichlorophenol-indophenol reduction) at all light intensities irrespective of the light quality during growth, and (b) the limiting step is light driven and located in the reaction center of photosystem II. Presumably, this same reaction determines the flow of electrons under low light intensities in vivo in cells from white, blue, and red light. In addition to photosynthesis, the rates of dark respiration changed due to the action of blue light. Concomitantly, the light compensation point of apparent photosynthesis was shifted during monochromatic irradiations.

DIURNAL PHOTOSYNTHETIC RESPONSES TO LIGHT BY MACROALGAE1,2

ABSTRACTThe diurnal variability of photosynthesis vs. irradiance (P‐I) curves was evaluated for the six most dominant species of macroalgae that occur annually in North Inlet Estuary, South Carolina. Three existing models best simulated the observed data: (1) the Hyperbolic Tangent Model of Jassby and Platt (1976), which was applied to data that showed no photoinhibition; (2) the Exponential Inhibition Model of Parker (1974); and (3) the Photoinhibition Model of Platt et al. (1980), which were employed when photo‐inhibition was measured. Photoinhibition was observed in about 75% of the experiments, and in some cases at irradiance levels as low as 500 μE.m−2. s−1. Most of the resulting P‐I curves did not differ significantly when measured at various times of the day. As a consequence of these results, we question conclusions expressed by others that it is not possible to accurately determine diurnal photosynthesis of macroalgae from light saturation curves that are measured over short time periods.

Standing stocks and productivity of phytoplankton off Westland, New Zealand, February 1982

Abstract In February 1982 there was an intense bloom of dinoflagellates close inshore off West‐land, New Zealand, and dinoflagellates also formed a large proportion of the phytoplankton offshore. Diatoms were present only at the bottom of the photic zone inshore off Wanganui Bluff, where dissolved nitrate‐nitrogen levels were elevated. Most biomass and production parameters were at least twice as large as in winter except for offshore biomass which was larger in winter. Weighted average chlorophyll a concentrations were negatively correlated with the depth of the mixed layer. The relative contribution which the vertical distribution of chlorophyll a, the production per unit chlorophyll a at optimal light intensities, and the initial slope of the light saturation curve made to the relationship between water column production per unit chlorophyll a and incident solar irradiance in inshore and offshore waters is discussed. In the non‐senescent inshore populations dominated by Prorocentrum micans, 91% of the ...

Photoecology of the coral Leptoseris fragilis in the Red Sea twilight zone (an experimental study by submersible).

Depth-dependent photoadaptational responses of the Red Sea zooxanthellate coral (Leptoseris fragilis) were studied down to 160 m from the research submersible GEO. Light saturation curves for photosynthesis revealed, with I C=1-2, I K=10.9 and I sat=20 μE·cm-2·sec-1, the lowest values of photokinetic parameters ever reported for a symbiotic coral. In summer, positive net production occurs only around noon at approx. 100m depth. Biomass parameters of corals at 100-135 m are negatively correlated with depth in algal cell density, protein, chlorophyll and carotenoid but not in pigment ratios or cell based pigment content. Coral size decreased with depth. Corals transplanted from 110-120 m original depth to 40, 70, 90 and 160 m showed high survival after one year. O2-production and dark O2-uptake increased with decreasing transplantation depth. After one year, transplants at 70 and 90 m but not at 40 m had higher algae density and pigment concentrations. The host light-harvesting systems described by Schlichter, Fricke and Weber (1986) are partially destroyed in 40 m but not in 70 and 90 m transplants. Different light exposures alter P-I-responses (P max, I C, I K, I sat) but not biomass parameters, indicating molecular or biochemical adaptation. The coraal's optimal light fields lie between 70 to 90 m. Its exceptional bathymetric distribution is linked with the newly discovered host light-harvesting systems which probably enhance photosynthetic performance in a dim environment.

Measurement of photosynthesisin vivowith a leaf disc electrode: correlations between light dependence of steady-state photosynthetic O2evolution and chlorophyllafluorescence transients

The application of a leaf disc electrode to the measurement of the quantum yield of photosynthetic oxygen evolution (in saturating carbon dioxide concentrations) is described. The technique was also used to characterize the light-saturation curves for photosynthesis in leaves of spinach plants grown in relatively low (‘shade’) and high (‘sun’) light intensities. It was found that the flux of a blue excitation light required to elicit oscillations in chlorophyllafluorescence corresponded, approximately, to the flux of (white) light required to saturate photosynthetic oxygen evolution. The requirement was higher for leaves of sun-grown plants (approximately 800 μmol m-2s-1) than for shade-grown plants (approximately 200 μmol m-2s-1). Brief pretreatment of leaf discs from sun-grown plants with D-mannose did not change the quantum yield, but lowered the light saturated rate and the photon flux density required to saturate photosynthesis. Oscillations in fluorescence could then be observed at lower fluxes of blue excitation light, similar to those required by leaves from shade-grown plants. Photoinhibition of shade-grown plants (exposed to full sunlight for 5 h) reduced quantum yield and increased the light flux required for saturation of photosynthesis. Oscillations in fluorescence, normally observed at low fluxes of blue light in these leaves, could not be detected after photoinhibition. These correlations are interpreted and applications of the techniques described are discussed.

Quantitative analysis of State 1–State 2 transitions in intact leaves using modulated fluorimetry — evidence for changes in the absorption cross-section of the two photosystems during state transitions

Using a combination of modulated and non-modulated light with synchronized detection it has been possible to monitor State 1–State 2 transitions in intact leaves as changes in the yield of modulated chlorophyll fluorescence. In the presence of excess far-red non-modulated light (713 nm) absorbed mainly by Photosystem I (PS I), the modulated fluorescence intensity was taken to represent F o — the emission yield which occurs when the reaction centres of Photosystem II (PS II) are all open. On the other hand, superimposing saturating non-modulated wide-band, blue-green light resulted in a transitory maximum yield of modulated chlorophyll fluorescence, F m, due to the total closure of the PS II reaction centres. In the absence of these additional lights the fluorescence level assumed a steady-state value, F s, between F o and F m. All these parameters changed as the leaf slowly adapted to light of a given spectral composition. It was found that both F o and F m increased reversibly (by about 15–20%) during the transition from State 2 to State 1 such that the ratio of F m to F o remained constant, indicative of changes in absorption cross-section of PS II and PS I rather than alterations in ‘spillover’ which would cause preferential changes in F m. It was also possible to estimate the fractions of light, β and α, channeled to PS II and PS I, respectively, from the values of F o, F m and F s. In one approach, β was estimated in State 1, using the assumption that α + β = 1, and its variation during the subsequent state transition was assumed to follow proportional changes in F o (or F m). It was found that in State 2 there is a small loss (about 4%) of the total utilization of light in both photosystems. However, if such loss is neglected, assuming α + β is always unity, the calculated β was found to vary in the same direction and almost with the same magnitude as F o (or F m), indicating independently that a change in absorption cross-section in PS II (and PS I) had occurred. Consistent with these data were the light-saturation curves for the non-modulated far-red light-quenching effect in bringing the fluorescence from F s to F o in States 1 and 2. The ratio of the initial slopes of these curves indicates quantitatively both redistribution of light between PS I and PS II during the State 1–State 2 transitions and a partial loss of excitation energy in State 2.

Reconstitution of energy transfer and electron transfer between solubilised pigment-protein complexes from thylakoid membranes. The role of acyl lipids

Solubilisation of thylakoid membranes from young leaves of Pisum sativum in the presence of Triton X-100 resulted in an almost complete loss of quenching of light-harvesting chlorophyll-protein (LHCP) fluorescence, as measured at 77°K. There were concomitant changes in the kinetics of light-saturation curves of electron transport from 2,6-dichlorophenolindophenol/ascorbate to methyl viologen. These effects were accompenied by a physical dissociation of LHCP polypeptides from photosystem I (PSI) and photosystem II (PSII) polypeptides, as determined by polyacrylamide gel-electrophoresis. Detergent-dialysis in the presence of exogenous purified galactolipids, about 80% of which were linoleoyl molecular species, only partially reversed these effects. However, detergent-dialysis using the phospholipids, phosphatidylglycerol and phosphatidylcholine, resulted in the substantial restoration of 77°K fluorescence quenching and the restoration of both emission spectra and electron transport kinetics of both Photosystems I and II that were typical of native membranes.

Anacystis nidulans Demonstrates a Photosystem II Cation Requirement Satisfied Only by Ca2+ or Na+

Anacystis nidulans exhibits a total loss of photosystem II (PSII) activity upon incubation in a nutrient medium deficient in Ca(2+) and Na(+) and containing a divalent cation chelator. This loss of activity is light-dependent, which corresponds to an energy requirement. Likewise, Ca(2+) efflux takes place only in cells incubated in light. The loss of PSII activity is reversible by addition of submillimolar amounts of either Ca(2+) or Na(+) to the external medium but not by the addition of any other cation. Restoration of lost PSII activity also requires light. Light saturation curves for partially depleted cells demonstrate both lower maximum O(2) evolution rates and decreased relative quantum yields when compared to control cells. Partial electron transport reactions isolate the site of the Ca(2+)/Na(+) effect to the reaction center itself or immediately on its oxidizing side and exclude the water-splitting complex. O(2) flash yields decline during cation depletion, indicating a decrease in the number of functional PSII reaction centers, but the maximum turnover rate for still functional reaction centers does not decline. Thus, PSII of A. nidulans exhibits an all-or-none cation requirement, satisfied only by Ca(2+) or Na(+).

PH dependence of the S 2 → S 3 transition associated with O 2 evolution in inside-out thylakoids

In inside-out vesicles, a large difference is observed in oxygen yield activity between pH 6.5 and 7.6 which is in contrast to right-side-out vesicles. The light saturation behaviour of the transition S 2 → S 3 also shows a pH dependence. In inside-out thylakoids, at pH 6.5, the light saturation curve of the S 2 → S 3 transitions exhibits 2 different light saturation processes whereas at pH 7.6 it resembles the light saturation behaviour of the other S-state transitions. This result is explained by the existence of a second donor in the S 2 state (different from the main donor), which contributes to about 30% of the S 2 → S 3 transitions at pH 6.5. This second donor needs to be protonated and thus, is not active at pH 7.6 in inside-out thylakoids.

Energetic aspects of the light activation of two chloroplast enzymes: fructose-1,6-bisphosphatase and NADP-malate dehydrogenase

The light energy requirements for photoactivation of two chloroplast enzymes: fructose-1,6-bisphosphatase and NADP-malate dehydrogenase were studied in a reconstituted chloroplast system. This system comprised isolated pea thylakoids, ferredoxin (Fd), ferredoxin-thioredoxin reductase (FTR) thioredoxinm and f (Tdm, Tdf) and the photoactivatable enzyme. Light-saturation curves of the photoactivation process were established with once washed thylakoids which did not require the addition of Td for light activation. They exhibited a plateau at 10 W·m(-2) under nitrogen and 50 W·m(-2) under air, while NADP photoreduction was saturated at 240 W·m(-2). Cyclic and pseudocyclic phosphorylations saturated at identical levels as enzyme photoactivations. All these observations suggested that the shift of the light saturation plateau towards higher values under air was due to competing oxygen-dependent reactions. With twice washed thylakoids, which required Td for enzyme light-activation, photophosphorylation was stimulated under N2 by the addition of the components of the photoactivation system. Its rate increased with increasing Td concentrations, just as did the enzyme photoactivation rate, while varying the target enzyme concentration had only a weak effect. Considering that Td concentrations were in a large excess over target enzyme concentrations, it may be assumed that the observed ATP synthesis was essentially dependent on the rate of Td reduction.Under air, Fd-dependent pseudo-cyclic photophosphorylation was not stimulated by the addition of the other enzyme photoactivation components, suggesting that an important site of action of O2 was located at the level of Fd.

Biophotolysis of water: the light saturation curves

Biophotolysis of water: the light saturation curves

Studies on the water-oxidizing system by the effects of different treatments in chloroplasts

Treatments such as trypsinization (50 μg/ml per mg Chl for 1 h), osmotic shock of the chloroplasts or mild heating altered the oxygen evolution in such a way that the properties of the Photosystem II were simplified. After these treatments, the damping of the oscillation pattern of O 2 yields induced by a flash series remained the same, irrespective of the level of inhibition induced by the treatment. This damping did not decrease with increasing flash energy, as observed in untreated chloroplasts. The light saturation curve of the S 2 → S 3 transition of the O 2 evolving system no more exhibited the slow-increasing phase at high flash energy observed under normal conditions. The kinetic properties of the O 2-evolving system were also simplified. After the treatments cited above, deactivation of S 2 and S 3 were identical and accelerated with respect to untreated chloroplasts. Turnover kinetics of the transitions S 1 → S 2 and S 2 → S 3 were also similar and simpler without a lag for S 2 → S 3. These results indicate that the treatments mentioned above disconnect one donor from the O 2-evolving complex. This donor, under normal conditions, contributes to the increase of the quantum yield of the transition S 2 → S 3 at high flash energy. This donor is here denoted by D. Our results are in agreement with the following working hypothesis: the large miss, observed on the S 2 → S 3 transition without any contribution of the donor D, may be due to the fact that the system needs a conformation change of the O 2-evolving complex in the S 2 state, so that the main donor Y can oxidize the second H 2O molecule in the water-splitting complex. In the inactive state corresponding to the absence of a conformation change, the donor D, being different in configuration, is likely to oxidize the S 2 state into an S 3 state at high light intensity.

INTERSPECIFIC VARIATION IN DARK NITROGEN UPTAKE BY DINOFLAGELLATES1

ABSTRACTSeven species of marine dinoflagellates were grown in nitrogen‐sufficient media under a 12:12 h L:D cycle, and then tested for their ability to take up nitrate and ammonium in the light and in the dark in short‐term experiments with 15N‐labelled substrate. The effect of the N substrate chosen, and the effect of sampling time in the L:D cycle, on the relative nitrogen content (the C:N ratio) was investigated at the same time. The physiological extremes in the material were represented by Prorocentrum minimum (Pav.) J. Schiller, which took up and presumably assimilated nitrate equally fast in the light and in the dark, and Gyrodinium aureolum Hulburt, which did not take up nitrate in the dark when in a state of nitrogen sufficiency. A strong coupling between nitrate assimilation and photosynthetic carbon assimilation in the latter species was suggested by the close similarity of the light saturation curves of 15NO3− and 14CO2 incorporation, and by a complete blocking of 15NO3− incorporation by 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU). Nitrogen starvation for 24 h induced a capacity in G. aureolum for taking up nitrate in the dark, or in the light in the presence of DCMU, a phenomenon that might be useful for identifying nitrogen limitation in this species in the field. Our study emphasizes the variability of dinoflagellate nitrogen nutrition and illustrates the difficulty of associating mass occurrences of dinoflagellates in nature with any particular nutritional mode.