Die Wirkung monochromatischen Lichts auf die extracelluläre Glykolsäure-Ausscheidung und die Lichtatmung bei der Blaualge Anacystis nidulans

Summary The algae were grown under normal air conditions in a low light intensity (400 lux) and measured in the normal CO₂-concentration (0.03 Vol. %). After an illumination period we observed a CO₂ gush which is dependent on the temperature and wavelength used during the measurements. At +20°C a CO₂ gush occurs only in the blue and far red regions. At +35°C, on the other hand, a CO₂ outburst appears over the whole spectrum. The magnitude of the CO₂ gush varies with the wavelength used during the light period. On this basis we have measured an action spectrum of photorespiration which is identical with the action spectrum of photosynthetic CO₂ uptake.Only at a low temperature (+20°C) and illumination with red light (550 to 651 nm; 10^-s einsteins/cm²·sec) did we find a light induced release of glycolate; in blue (432 and 473 nm; 10^-s einsteins/cm²·sec) and far red light (681 and 703 nm; 10^-8 einsteins/cm²·sec) no glycolate excretion occurred. But after addition of -hydroxy-2-pyridylmethane sulfonate (10^-3M) glycolate was excreted during illumination with all used wavelengths. The magnitude of glycolate production was nearly the same in all cases. No glycolate excretion occurred at +35°C in the whole region of the spectrum. Here, too, the addition of -HPMS forced release of glycolate in all wavelengths, indicating that glycolate biosynthesis was occurring.The results are discussed with reference to the physiological behaviour of the algae and activation of photorespiration in blue light. The obtained action spectrum of photorespiration is explained on the basis of a close relationship to photosynthesis.     

Photosynthetische carboxylierungsreaktionen verschieden pigmentierter Anacystis-zellen

Summary CO₂ exchange, ¹⁴CO₂ fixation and ¹⁴C-labelled photosynthetic products of differently pigmented Anacystis nidulans (strain L 1402-1) were studied during the induction period at +30°C. The algae were grown at +35° C in an atmosphere of 0.04 vol.-% CO₂ and measured under the same low CO₂ concentrations. Changing the culture conditions caused alterations in the pigment composition. Under normal illumination (white light; 0.6×10³ erg/ cm² s) the relation between amounts of chlorophyll a and phycocyanin was 1:7 to 1:10. In a high light intensity (30.8×10³ erg/cm² s) the phycocyanin content was reduced (1:5 to 1:2). When the cells were grown in red light of high intensity (20×10³ erg/ cm² s) phycocyanin synthesis increased; the pigment ratio varied between 1:20 and 1:33. Anacystis cells grown under strong white light were filamentous.Photosynthetic CO₂ uptake, measured with an infrared gas analyzer, was very low in algae grown in high light intensity. The pattern of ¹⁴C-labelled photosynthetic products of these algae was very similar to those of the Calvin cycle. In Anacystis cells grown under low intensities of white light or in red light ¹⁴CO₂ was, at the beginning of the light period, incorporated mainly into aspatate and glycerine/serine. The enzyme activities of NAD⁺-specific malate dehydrogenase, ribulose-1,5-diphosphate carboxylase, aspartate and alanine aminotransferase decreased with increasing phycocyanin content. NADP⁺-specific malic enzyme activities showed practically no change. In contrast, phosphoenolpyruvate carboxylase activity increased with a higher rate of phycocyanin synthesis. In another series of experiments the behaviour of the PEP carboxylase activity after breakdown of the Anacystis cells was tested in differently pigmented cultures. In all cases the enzyme activities very rapidly decreased within two hours. The results obtained are discussed with reference to the correlation of pigment composition and CO₂ fixation of the phosphoenolpyruvate system.

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Abkürzungen Asp Aspartat - Gly/Ser Glycin/Serin - PGS 3-Phosphoglycerat - ZmP Zuckermonophosphat Herrn Professor Dr. Andre Pirson in Verehrung gewidmet     

Investigation of electrophysiological responses of Neurospora crassa to blue light

The influence of light in a spectrum range of 350–500 nm 20 W m^-2 (20,000 erg · cm^-2 · s^-1) has been studied in the mycelial cells of Neurospora crassa. Light-induced input resistance and membrane potential changes can be measured by means of intracellular microelectrodes. The value of the input resistance reached maximum after a 2–5 min illumination. The maximum hyperpolarization of the cell membrane reaching 30–40 mV was observed after 20–25 min illumination, when the input resistance values did not differ significantly in the illuminated and non-illuminated cells.     

Action spectra for photosynthetic adaptation in Scenedesmus obliquus

Photosynthetic adaptation of the unicellular green alga Scenedemus obliquus to different light conditions was investigated with respect to chlorophyll synthesis. Cultures were grown under white light (20 W · m^–2) from fluorescent lamps and were then transferred and subjected to the actual adaptation regime which consisted of a 24-h irradiation by different fluence rates and wavelengths. Fluence rate-response curves for chlorophyll synthesis were measured between 4 · 10^–2 and 1 · 10² W · m^–2. In white light from incandescent lamps, in blue and red light the fluence rate-response curves for chlorophyll (Chl) a and also for Chl b were bell-shaped. In red light the threshold was about the same as under blue light. The maximal amounts of Chl a and b were about twofold increased under blue light relative to the values obtained with red light. Action spectra for the stimulation of chlorophyll synthesis (Chl a + Chl b) as well as those for the separate chlorophylls showed two maxima near 450 and 500 nm. However, the action spectrum for Chl b synthesis demonstrated a considerably higher value in the 450-nm peak. Experiments with the photosynthesis inhibitor 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) indicated that photosynthetic energy supply supported the photostimulation of chlorophyll synthesis. The action spectra indicate the cooperation of two photoreceptors. The 460-nm peak is attributed to the typical blue-light receptor, being more active in Chl b formation. The peak at 500 nm may represent carotenoproteins acting as an accessory pigment system.Abbreviations PCV packed cell volume - Chl total amount of chlorophyll - Chl a, b chlorophyll a, b - DCMU 3-(3,4-dichlorphenyl)-1,1-dimethylurea This project was supported by the Deutsche Forschungsgemeinschaft. We thank Ms. K. Bölte for technical assistance.     

Sensitivity to far-red radiation in stomata of Phaseolus vulgaris L.: Rhythmic effects on conductance and photosynthesis

The influence of far-red (FR; 700–800 nm) radiation on steady-state stomatal conductance and net photosynthesis in P. vulgaris has been studied. Whereas FR radiation alone was relatively ineffective, addition of FR to a background of white light (WL; predominantly 400–700 nm) resulted in increased stomatal conductance. Stomata exhibited a marked diurnal sensitivity to FR. The action maximum for enhancing stomatal conductance was near 714 nm. A combination of FR and infra-red (IR; >800 nm) enhanced net photosynthesis when added to a background of WL. When IR alone was added to WL, there was a net decrease in photosynthesis, indicating that it is the FR waveband which is responsible for the observed photosynthetic effects. Naturally occurring levels of FR radiation (235 mol·m^-2·s^-1) in vegetation-canopy shade enhanced net photosynthetic CO₂ gain by 28% when added to a background of 55 mol·m^-2·s^-1 WL.Abbreviations BL blue - FR far-red - IR infra-red - PAR photosynthetically active radiation - R red - WL white light     

Untersuchung der Beziehung zwischen extracellulärer Glykolsäure-Ausscheidung und der photosynthetischen CO2-Aufnahme bei der Blaualge Anacystis nidulans

Summary The formations of transients in CO₂ exchange in the blue-green alga Anacystic nidulans is dependent on the temperature used during the measurements. The algae were grown in a low light intensity (4000 lux) under normal air conditions and measured in the same low CO₂ concentration (0.03 vol. %) but under a higher light intensity (10 000 lux). At a temperature of +20°C the stationary rate of CO₂ uptake was reached directly. At a temperature of +35°C, on the other hand, a maximum of CO₂ uptake could be observed at the beginning of the light period followed by a steady rate of photosynthesis, which was higher than at +20°C. In the beginning of the dark period a CO₂ outburst appeared at 35°C.Only at a low temperature (+20°C) did we find a light induced glycollate excretion; after a maximum at 7 1/2 minutes illumination the release of glycollate ceases and the level decreases to a lower value. A similar time course exists during illumination in red light (621 nm, 1.5·10^-8 einsteins) and a temperature of +20°C. In blue light (432 nm, 1,5·10^-8 einsteins, +20°C) and in white light at a high temperature (+35°C) we could not find any light induced glycollate excretion. Our results are discussed in reference to the photorespiration. We explain the formation of transients in CO₂ uptake of Anacystis at a high temperature (+35°C) and in blue light (+20°C) on the basis of the influence of photorespiration.     

Effects of intensity and quality of light on phycocyanin production by a marine cyanobacterium Synechococcus sp. NKBG 042902

Among 150 strains, including marine cyanobacteria isolated from coastal areas of Japan and a freshwater cyanobacterium from the IAM collection, Spirulina platensis IAM M-135, the marine cyanobacterium Synechococcus sp. NKBG 042902 contained the highest amount of phycocyanin (102 mg/g dry cell weight). We have proposed that the cyanobacterium could be an alternative producer for phycocyanin. The effects of light intensity and light quality on the phycocyanin content in cells of Synechococcus sp. NKBG 042902 were investigated. When the cyanobacterium was cultured under illumination of 25 mol m^–2 s^–1 using a cool-white fluorescent lamp, the phycocyanin content was highest, and the phycocyanin and biomass productivities were 21 mg 1^–1 day^–1 and 100 mg 1^–1 day^–1 respectively. Red light was essential for phycocyanin production by this cyanobacterium. Phycocyanin and biomass production were carried out by the cyanobacterium cultures grown under only red light (peak wavelength at 660 nm) supplied from light-emitting diodes (LED). Maximum phycocyanin and biomass productivities were 24 mg 1^–1 day^–1 and 130 mg 1^–1 day^–1 when the light intensity of the LED was 55 mol m^–2 s^–1.     

Der Einfluß von Licht auf die Atmung von Chlorella bei gehemmter Photosynthese

Summary On illumination with blue light the O₂-uptake of Chlorella pyrenoidosa (211-8b) in which photosynthetic O₂-liberation has been suppressed by 10^-5M DCMU initially decreases, but in the course of 5–10 min increases over that in preceding darkness (Fig. 1). Whereas an enhancement of O₂-uptake is already induced by traces of blue radiation and saturated at about 1.5x10^-10einsteins cm^-2sec^-1, the initial inhibition of O₂-uptake can be measured only after application of more than 1.5×10^-10einsteins cm^-2sec^-1 (Fig. 2).The long induction time that passes before a steady enhancement in O₂-uptake is reached, the low energy requirement of the enhancement, and its spectral dependence with greatest efficiency of wavelengths around 455 nm and 375 nm and no effect of wavelengths beyond 520 nm (Fig. 3) resemble the corresponding data found earlier for an enhancement of respiration by light in a chlorophyll-free, carotenoidcontaining Chlorella mutant. It is therefore likely that the increased O₂-uptake in DCMU-poisoned cells of wild type Chlorella depends on an increase in respiration. The pigment involved is not known, but from the action spectrum it could be a flavin or a cis-carotenoid.In contrast to the increase the initial decrease in O₂-uptake does not show up in strong blue light only, but is also present in red light in which it stays constant throughout the period of measurement of 20 min (Fig. 4). Its intensity dependence is similar in blue and in red light; the lower efficiency of blue, which appears in Fig. 5, is at least partially due to the time interval of 5 min chosen for its determination: in these first 5 min after the beginning of blue illumination the slow increase in respiration already begins. The spectral dependence of the decrease in O₂-consumption in the red part of the visible spectrum yields greatest activity around 680 nm, a slow drop towards 525 nm and a steep one towards 743 nm (Fig. 6). From that and the absence of any after-effect of red light on the O₂-consumption in following darkness (Fig. 8), which might be expected if phytochrome action were involved, we think chlorophyll to be the pigment responsible for light-dependent inhibition of O₂-uptake. A mutant of Scenedesmus, Bishop's Nr. 11, which is unable to evolve photosynthetic oxygen, behaves just like DCMU-poisoned Chlorella (Fig. 7). We therefore consider the decreased O₂-consumption in the light to result from a partial inhibition of respiration and not from remaining photosynthesis unaffected by 10^-5M DCMU. As photosystem I still operates in Bishop's mutant 11 as well as in DCMU-poisoned Chlorella, illumination might lead to an accumulation of ATP by cyclic photophosphorylation and thus to a lowering of the cellular ADP level. This could result in a slowing down of glycolysis and consequently of respiratory O₂-uptake.     

The recovery of photosynthesis in tomato subsequent to chilling exposure

The overall success of a plant in coping with low temperature sensitivity of photosynthesis is dependent not only on the maximum extent of inhibition suffered for a given time of low temperature exposure but also on the persistence of the inhibition after normal growth temperatures are restored. Thus the capacity of recovery and the speed with which a plant can recover from the effects of chilling exposure are important parameters in determining how devastating the chilling event will be on season-long growth and yields. We have studied the recovery of CO₂-saturated photosynthesis from the injury caused by exposing intact tomato plants (Lycopersicon esculentum Mill. cv. Floramerica) or detached tomato leaves to a temperature of 1°C in the dark for varying periods of time. We found that net photosynthesis was fully recovered within 12 h after returning the plants to 25°C in the dark, even after chilling exposures as long as 45 h. This was true for intact plants as well as for detached leaves that were supplied with water. When chilling took place in the light (4°C, 1000 E · m^-2 · s^-1, PAR) inhibition of photosynthesis was more severe and appeared more quickly and the recovery was slower and incomplete. A 12 h chilling exposure in the light resulted in injury to net photosynthesis that was not fully recovered even after 50 h. Chilling damage to photosynthesis developing in the light was distinguished from chilling in the dark by the decreased photosynthetic quantum yield. Not only did high intensity illumination enhance chilling damage of photosynthesis but bright light subsequent to the chilling exposure also delayed the recovery of photosynthesis. At none of the three ambient CO₂ concentrations investigated (300, 1500 and 5000 1.1^-1) did the recovery of photosynthesis depend on stomatal conductance.     

Der Einfluß von Rot- und Blaulicht auf die Photosynthese vonAcetabularia mediterranea und auf die Verteilung des assimilierten Kohlenstoffs

Zusammenfassung Bei Zellen der marinen Grünalge Acetabularia mediterranea liegen nach 2stündiger Photosynthese im Weißlicht (8000 Lux) etwa 80% des fixierten¹⁴C in äthanollöslicher Form vor, etwa 12% entfallen auf Stärke, 2–3% auf Protein und 6% auf die Zellwand.Werden die Zellen mit Rotlicht (Dauerlicht, 3800 erg · cm^–2 · sec^–1) bestrahlt, so fällt die Einbaurate in allen 4 Fraktionen stark ab (Abb. 1). Dabei nimmt der¹⁴C-Anteil in der äthanollöslichen Fraktion innerhalb von 3 Wochen zu Lasten der Stärke und Zellwand von 80% auf ca. 90% zu. Im Gegensatz dazu wird im Blaulicht (Dauerlicht, 5600 erg · cm^–2 · sec^–1) mit der Bestrahlungsdauer der Einbau in Stärke, Zellwand und Protein gefördert (Abb. 1).Trotz sinkender Einbauraten von¹⁴C in Stärke nimmt im Rotlicht der Stärkegehalt pro Zelle zu, liegt dagegen im Blaulicht trotz höherer¹⁴C-Einbauraten deutlich unter demjenigen der Rotlichtzellen (Tabelle 1 und 2). Die Akkumulation von Stärke im Rotlicht dürfte demnach auf einer Hemmung des Stärkeabbaus beruhen.Der Gehalt an löslichen Kohlenhydraten (Fructose, Glucose, Saccharose, Fructosane) stagniert in Rotlichtzellen und steigt in Blaulichtzellen um ein Mehrfaches an (Tabelle 1).Bestrahlung mit Blaulicht nach Rotlichtvorbehandlung führt zu einem Ansteigen der Photosyntheseintensität. Nach 8stündiger Bestrahlung nimmt die Fixierungsrate zu und erreicht nach 48- bis 72stündiger Bestrahlung etwa das 5- bis 6fache des am Ende der Rotlichtbestrahlung gemessenen Wertes (Abb. 2).Diesem Anstieg der Fixierungsrate muß offenbar eine Synthese von Proteinen vorausgehen (Abb. 3). Auch der¹⁴C-Einbau in Stärke und die Zellwand steigt bereits vor der Gesamtfixierung an, und außerdem wird der Abbau der während der Rotlichtvorbehandlung akkumulierten Stärke eingeleitet (Tabelle 2).Der Hauptanteil des¹⁴C in der löslichen Fraktion entfällt auf die löslichen Kohlenhydrate. Bestrahlung mit Blaulicht nach Rotlichtvorbehandlung führt zunächst zu einer Abnahme des¹⁴C-Einbaus in die löslichen Kohlenhydrate, gefolgt von einem starken Anstieg bis zur 72. Stunde und einem erneuten Abfall (Abb. 4). Während der¹⁴C-Einbau in Fructose, Saccharose und Glucose diesem Kurvenverlauf folgt, steigt der Einbau in Inulin bis zur 72. Stunde kontinuierlich an (Abb. 5).Demgegenüber ist der auf die basische (Aminosäuren) und die saure Fraktion entfallende Anteil gering. Der¹⁴C-Einbau in beide nimmt im Blaulicht kontinuierlich zu (Abb. 4). Aminosäuren werden in den Zellen auch nach 3wöchiger Bestrahlung mit Rotlicht gebildet. Ferner ist der Gehalt an Aminosäuren am Ende der Rotlichtvorbehandlung am höchsten (Tabelle 3). Die Syntheserate von Protein in Rotlicht dürfte demnach nicht durch die Aminosäurekonzentration begrenzt werden.Die Ursache für den Abfall der Photosyntheseintensität bei Rotlichtbestrahlung ist den vorliegenden Daten nicht zu entnehmen. Die Möglichkeiten, die dabei eine Rolle spielen könnten, werden diskutiert.

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The effect of red and blue light on photosynthesis ofAcetabularia mediterranea and on the distribution of assimilated carbon

Summary After photosynthesis for two hours in white light (8000 lux), cells of the marine chlorophycean algaAcetabularia mediterranea contain about 80% of the¹⁴C incorporated in ethanol soluble form, about 12% in starch, 2–3% in protein, and 6% in the cell wall.When cells are irradiated with red light (continuous light, 3800 erg · cm^–2 · sec^–1), the incorporation rate for all four fractions is sharply reduced (Fig. 1). Concomitantly, the¹⁴C content in the ethanol soluble fraction rises in three weeks from 80% to about 90%, to the debit of starch and cell wall. In contrast to these findings, incorporation into starch, cell wall, and protein under blue light (continuous light, 5600 erg · cm^–2 · sec^–1) rises with the irradiation time (Fig. 1).Starch content per cell rises under red light in spite of declining incorporation rates of¹⁴C into starch, whereas it is clearly reduced in blue light below the values for red light cells, notwithstanding the increased¹⁴C incorporation rates (Tables 1 and 2). Accumulation of starch under red light seems to be due, therefore, to an inhibition of starch degradation.Soluble carbohydrate content (fructose, glucose, sucrose, fructosans) stagnates in red light cells and is multiplied in blue light cells (Table 1).Blue light irradiation after red light pretreatment increases the intensity of photosynthesis. The assimilation rate rises after an irradiation period of eight hours, reaching, after 48 to 72 hours of irradiation, about five to six times the level at the end of the red light period.Obviously, this rise in the assimilation rate must be preceded by protein synthesis (Fig. 3).¹⁴C incorporation into starch and cell wall rises even before the increase in total fixation, too, and, in addition, degradation of starch accumulated during the red light pretreatment is initiated (Table 2). The main amount of¹⁴C in the soluble fraction falls to soluble carbohydrates. Irradiation with blue light after red light pretreatment results at first in a reduction of¹⁴C incorporation into soluble carbohydrates, followed by a sharp increase till the 72nd hour and another decline (Fig. 4).¹⁴C incorporation into fructose, sucrose, and glucose follows this pattern, whereas incorporation into inulin increases continuously till the 72nd hour (Fig. 5).The amount falling to the basic and the acid fractions is small, in contrast.¹⁴C incorporation into both fractions rises continuously in blue light (Fig. 4).Amino acids are formed in the cells even after a three-week period of red light irradiation. Furthermore, the amino acid content is highest at the end of the red light pretreatment (Table 3). Thus, the rate of protein synthesis in red light seems not to be limited by amino acid concentration.The cause for the reduction of photosynthesis under irradition with red light does not become obvious from the data obtained. Factors possibly playing a role in this process are discussed.

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Die Untersuchungen wurden durch Sachmittel der Deutschen Forschungsgesellschaft unterstützt. Frau I. MAASS danke ich für die sorgfältige Mithilfe bei den Versuchen.     

Light-emitting diodes as a light source for photosynthesis research

Light-emitting diodes (LED) can provide large fluxes of red photons and so could be used to make lightweight, efficient lighting systems for photosynthetic research. We compared photosynthesis, stomatal conductance and isoprene emission (a sensitive indicator of ATP status) from leaves of kudzu (Pueraria lobata (Willd) Ohwi.) enclosed in a leaf chamber illuminated by LEDs versus by a xenon arc lamp. Stomatal conductance was measured to determine if red LED light could sufficiently open stomata. The LEDs produced an even field of red light (peak emission 656±5 nm) over the range of 0–1500 mol m^-2 s^-1. Under ambient CO₂ the photosynthetic response to red light deviated slightly from the response measured in white light and stomatal conductance followed a similar pattern. Isoprene emission also increased with light similar to photosynthesis in white light and red light. The response of photosynthesis to CO₂ was similar under the LED and xenon arc lamps at equal photosynthetic irradiance of 1000 mol m^-2 s^-1. There was no statistical difference between the white light and red light measurements in high CO₂. Some leaves exhibited feedback inhibition of photosynthesis which was equally evident under irradiation of either lamp type. Photosynthesis research including electron transport, carbon metabolism and trace gas emission studies should benefit greatly from the increased reliability, repeatability and portability of a photosynthesis lamp based on light-emitting diodes.     

Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with “antisense” rbcS

Tobacco (Nicotiana tabacum L.) plants transformed with antisense rbcS to decrease the expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances. Tobacco plants were grown in controlled-climate chambers under ambient CO₂ at 20°C at 100, 300 and 750 mol·m^–2·s^–1 irradiance, and at 28°C at 100, 300 and 1000 mol·m^–2·s^–1 irradiance. (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco (C _infRubisco ^supA ) was very low (0.01–0.03) at low growth irradiance, and still fairly low (0.24–0.27) at higher irradiance. (ii) Short-term changes in the irradiance used to measure photosynthesis showed that C _infRubisco ^supA increases as incident irradiance rises, (iii) When low-light (100 mol·m^–2·s^–1)-grown plants are exposed to high (750–1000 mol·m^–2·s^–1) irradiance, Rubisco is almost totally limiting for photosynthesis in wild types. However, when high-light-grown leaves (750–1000 mol·m^–2·s^–1) are suddenly exposed to high and saturating irradiance (1500–2000 mol·m^–2·s^–1), C _infRubisco ^supA remained relatively low (0.23–0.33), showing that in saturating light Rubisco only exerts partial control over the light-saturated rate of photosynthesis in sun leaves; apparently additional factors are co-limiting photosynthetic performance, (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight. As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the light reactions and Rubisco; this was shown by the low value of C _infRubisco ^supA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance. In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance. We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions, (v) Antisense plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight. They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown. We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light.Abbreviations A rate of photosynthesis - C _infRubisco ^supA flux control coefficient of Rubisco for photosynthesis - c_i internal CO₂ concentration - qE energy-dependent quenching of chlorophyll fluorescense - qQ photochemical quenching of chlorophyll fluorescence - NADP-MDH NADP-dependent malate dehydrogenase - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase - RuBP ribulose-1,5-bisphosphate This work was supported by the Deutsche Forschungsgemeinschaft (SFB 137).     

Light quality affects photosynthesis and leaf anatomy of birch plantlets in vitro

Cultures in vitro of Betula pendula Roth were subjected to light of different spectral qualities. Photosynthetic capacity was highest when the plantlets were exposed to blue light (max recorded photosynthesis, 82 mol CO₂ dm^–2 h^–1) and lowest when irradiated with light high in red and/or far-red wave lengths (max recorded photosynthesis, 40 mol CO₂ dm^–2 h^–1). Highest chlorophyll content (2.2 mg dm^–2 leaf area) was found in cultures irradiated with blue light, which also enhanced the leaf area. Morphometric analysis of light micrographs showed that the epidermal cell areas were largest in plantlets subjected to blue light and smallest in those subjected to red light. Morphometric analysis of electron micrographs of palisade cells, showed that the functional chloroplast area was largest in chloroplasts of leaves subjected to blue light and smallest in those exposed to red light. We suggest that light quality affects photosynthesis both through effects on the composition of the photosynthetic apparatus and on translocation of carbohydrates from chloroplasts.     

Analysis of oxygen evolution during photosynthetic induction and in multiple-turnover flashes in sunflower leaves

Exchange of CO₂ and O₂ and chlorophyll fluorescence were measured in the presence of 360 1 · 1^–1 CO₂ in nitrogen in Helianthus annuss L. leaves which had been preconditioned in the dark or at a photon flux density (PFD) of 24 mol · m^–2 · s^–1 either in 21 or 0% O₂. An initial light-dependent O₂ outburst of 6 mol · m^–2 was measured after aerobic dark incubation. It was attributed to the reduction of electron carriers, predominantly plastoquinone. The maximum initial rate of O₂ evolution at PFD 8000 mol · m^–2 · s^–1 was 170 mol · m^–2 · s^–2 or about four times the steady CO₂-and light-saturated rate of photosynthesis. Fluorescence measurements showed that the rate was still acceptor-limited. Fast O₂ evolution ceased after electron carriers were reduced in the dark-adapted leaf, but continued for a short time at the lower rate of 62 mol · m^–2 · s^–1 in the light-adapted leaf. The data are interpreted to show that enzymes involved in 3-phosphoglycerate reduction are dark-inhibited, but were fully active in low light. In a dark-adapted leaf, respiratory CO₂ evolution continued under nitrogen; it was partially inhibited by illumination. Prolonged exposure of a leaf to anaerobic conditions caused reducing equivalents to accumulate. This was shown by a slowly increasing chlorophyll fluorescence yield which indicated the reduction of the PSII acceptor Q_A in the dark. When the leaf was illuminated, no O₂ evolution was detected from short light pulses, although transient O₂ production was appreciable during longer light pulses. This indicates that an electron donor (pool size about 2–3 e/PSII reaction center) became reduced in the dark and the first photons were used to oxidise this donor instead of water.Abbreviations Chl chlorophyll - CRC carbon reduction cycle - GAPDH NADP-glyceraldehyde-phosphate dehydrogenase - PFD photon flux density - PGA 3-phosphoglycerate - RuBP ribulose bisphosphate - TCA tricarboxylic acid cycle To whom correspondence should be addressedThis work received support by the Estonian Academy of Sciences, the Gottfried-Wilhelm-Leibniz Program of the Deutsche For-schungsgemeinschaft and the Sonderforschungsbereich 251 of the University of Würzburg.     

Eine fördernde Wirkung von Blaulicht auf die Carotinoidbildung einer gelben Chlorella-Mutante

Summary In growing as well as in resting cells of a chlorophyll-free yellow mutant of Chlorella vulgaris (211-11h/20) synthesis of carotenoids is enhanced by blue light. Permanent irradiation is necessary to maintain the effect (Fig. 2). At wavelengths around 454 nm the additional carotenoid production is half-saturated at about 1000 erg cm^-2s^-1 and saturated at about 4000 erg cm^-2s^-1 (Fig. 3). An action spectrum exhibits highest efficiency of wavelengths around 465 and 370 nm, a minimum near 400 nm and inefficacy of yellow, red and far-red light (Fig. 4). This wavelength dependence resembles those of light enhanced O₂-uptake, carbohydrate consumption and gain of organically bound nitrogen by the organism.     

Inhibition of aggregation by light in the cellular slime mold Dictyostelium discoideum

Aggregation of Dictyostelium amoebae is inhibited by light. White light intensities 10² W · cm^-2 cause an inhibition which reaches a saturation at 2 · 10³ W · cm^-2. The action spectrum, based on photon fluence-response curves, shows a major peak around 405 nm and extends through most of the visible spectrum with a secondary maximum at about 530 nm. The action spectrum of the inhibition of aggregation resembles the action spectrum of accumulations of amoebae in light traps and the action spectrum of photodispersal from light traps; it does not resemble the action spectrum of phototaxis in pseudoplasmodia.     

Elektron-Spin-Resonanz-Untersuchungen der Reaktionskinetik strahleninduzierter freier Radikale des Cholesterins

Zusammenfassung Die Reaktionskinetik strahleninduzierter freier Radikale des Cholesterins wurde in flüssiger Phase bei Raumtemperatur mittels ESR-Spektroskopie untersucht. Mit Hilfe eines geeigneten photochemischen Initiationssystems ließen sich in Cyclohexanlösung unter UV-Bestrahlung (235 nm265 nm) genau dieselben freien Radikale des Cholesterins darstellen, die schon früher [9, 7] in röntgenbestrahltem Cholesterinpulver beobachtet worden waren. Bei ausreichendem O₂-Partialdruck (3·10⁴Torr) über der Probenlösung trat das ESR-Spektrum eines Peroxyradikals auf, das mittels der Analyse seiner Reaktionsprodukte (7-Hydroxy-Cholesterin und 7-Keto-Cholesterin) mit dem Cholesteryl-7-peroxyradikal identifiziert wurde. Die Kinetik sowohl der Bildung als auch des Zerfalls des Radikals entsprachen einer Reaktion von 2. Ordnung. Die Geschwindigkeitskonstante für den bimolekularen Zerfall, eine Disproportionierung in Alkohol und Keton unter Abgabe eines Moleküls O₂, wurde bei Raumtemperatur zuk ₂=(1,8 _–0,6 ^+0,9 )·10⁶ sec^–1M^–1·l bestimmt. Ferner wurde gezeigt, daß das Cholesteryl-7-peroxyradikal aus dem freien Radikal Cholesteryl-7 durch Anlagerung eines Moleküls O₂ entsteht. Für die Geschwindigkeitskonstante dieser Reaktion ergab sich eine untere Schranke vonk ₁=0,40·10¹⁰ sec^–1M^–1·l.

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Electron spin resonance investigations on radiation-induced free radicals of cholesterol in liquid phase

Summary The reaction kinetics of radiation-induced free radicals of cholesterol was studied in liquid phase at room temperature by means of e.s.r. spectroscopy on a solution of cholesterol in cyclohexane. Using a convenient photochemical initiation system, just those free radicals of cholesterol could be generated by the filtered u.v. radiation from a Xe high pressure lamp (235 nm265 nm) as were observed already a decade ago by Gordy [9] and by Ehrenberg, Löfroth [7] in X-irradiated cholesterol powder. At sufficiently high O₂-pressures (3·10^–4 Torr) over the sample solution a peroxy radical e.s.r. spectrum arose during u.v. irradiation which was identified by product analysis (7-hydroxy-cholesterol and 7-keto-cholesterol) to be dueto a cholesteryl-7-peroxyradical. The radical'sgeneration and decay kinetics was governed by a second order reaction. The velocity constant for bimolecular decay of the cholesteryl-7-peroxyradical was found to be k₂=(1.8 _–0,6 ^+0,9 )·10⁶sec^–1M^–1·l at room temperature. Furthermore it could be shown that the cholesteryl-7-peroxyradical was built up by the addition of one molecule of O₂ to a cholesteryl-7 free radical. For this reaction a value ofk ₁=0.4·10¹⁰ sec^–1 M^–1·l was estimated as a lower limit of the velocity constant.

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Die Arbeit stellt einen Auszug aus einer Dissertation an der Technischen Hochschule München dar.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Internally illuminated photobioreactor using a novel type of light-emitting diode (LED) bar for cultivation of <Emphasis Type="Italic">Arthrospira platensis</Emphasis>

The biochemical properties of Spirulina platensis in an internally illuminated photobioreactor (IlPBR) were investigated under different light-emitted diode (LED) wavelengths; blue (λ_max= 450 and 460 nm), green (λ_max= 525 nm), red (λ_max = 630 and 660 nm), and white (6,500K), with various light intensities (200, 500, 1,000, and 2,000 μmol/m²/sec) were examined. The highest specific growth rate, maximum biomass, and phycocyanin productivity occurred under the red LEDs (0.39/day, 0.10 g/L/day, and 0.14 g/g-cell/day, respectively) at 1,000 μmol/m²/sec; the lowest growth rate was obtained under blue LEDs. Indeed, the size of trichomes was changed into short form under blue LEDs at all light intensities or all LEDs at 2,000 μmol/m²/sec for the first 2 days after inoculation, and S. platensis did not grow in the IlPBR under the dark condition. These results provide a base for different approaches for designing the pilot scale photobioreactor and developing cost-effective light sources.     

Phototrophic growth in the lumostat: a photo-bioreactor with on-line optimization of light intensity

A novel approach is described for the growth of phototrophic microorganisms in batch culture in laboratory-scale photo-bioreactors. Pure CO₂ is added separately to the aeration gas in a closed loop and the rate of photosynthetic activity is monitored continuously by recording the amount of CO₂ added in order to maintain constant pH. These activity measurements are used to control the intensity of illumination by varying the voltage applied to a bank of fluorescent tubes. The intensity of illumination is maintained at the value giving the maximal rate of photosynthesis while photoinhibition due to excess light is avoided. Since the light intensity received by the individual cells is maintained at the optimal value we term the device a lumostat.Measurements of photosynthetic activity by monitoring CO₂ addition were in excellent agreement with off-line measurements of cell carbon as long as corrections were made for diffusion loss through the walls of the tubing. Exponential growth of a thermophilic strain of the cyanobacteriumSynechococcus was obtained for 7 generations with maximum cell densities of 8 × 10⁷ cells mL^–1. The productivity of the lumostat is superior to that of batch cultures at any fixed light intensity.