Azione Della Luce Sull'Assorbimento,L'Utilizzazione Ed Il Trasporto Dei Glucidi

Abstract

Effect of light on the uptake, utilization and transport of sugars. — The effect of light on the uptake of saccharides, their incorporation into insoluble fractions and their transport by green tissues has been studied under conditions of complete inhibition of the photosynthetic assimilation of CO₂. Such conditions were obtained by means of either an inhibitor of O₂ evolution (CMU), or by running the experiment in CO₂-free atmosphere. When Wolffia arryza plants are incubated with glucose-C¹⁴, light stimulates the incorporation of C¹⁴ into all fractions examined, and especially into the polysaccharides, like cellulose,' which are synthesized outside the chloroplasts.

Experiments with Elodea canadensis have shown that light stimulates the transport of glucose-C¹⁴ from the leaves to the stems, independently of the presence or absence of CO₂ assimilation.

These experiments support the hypothesis that ATP synthesyzed in the light by chloroplasts can be utilized by green cells as an energy source for biosyntheses outside the plastids, as well as for other types of biological work, such as active uptake and transport.     

Sul Metabolismo Dell'Alcool Etilico in Tessuti Di Fusto Di « Pisum »

Abstract

On the metabolism of ethanol in the Pea stem tissues. — The average concentration of ethanol in the growing part of the etiolated pea internodes is of the order of 10^-3M. Previous work showed that auxin at growth promoting concentration markedly lowers this level in the excised internodes. This finding prompted a series of investigations on C¹⁴ labeled ethanol utilization in this material.

The capacity of the segments to metabolize ethanol is remarkable: with an external ethanol concentration 5X10^-3M the C¹⁴ labeled CO₂ originated from 1-C¹⁴ ethanol accounted for about 10% of total CO₂ produced during the first hour of treatment. Moreover, an amount of ethanol about 10 fold higher that that dissimilated to CO₂ was metabolized to various yet unidentified compounds. The ratio between the contribution of ethanol to CO₂ and that to other metabolites appeared maximal in the first period after feeding the labeled compound. This ratio was significantly higher then that found for 6-C¹⁴ glucose.

These preliminary results suggest the possibility that ethanol produced in glycolysis could represent an interesting metabolite in an anabolic pathway different from the one leading from pyruvate to the Krebs cycle acids.     

Effetto Del Dinitrofenolo Sulla Conversione Del Glicerolo A Glucidi in Fettine Di Carote E in Internodi Di Pisello

Abstract

On the effect of dinitrophenol on carbohydrate activation in higher plant tissues. — Previous investigations on the effects of 2,4 dinitrophenol (DNP) on carbohydrate metabolism in isolated pea internodes and in yeast showed that the increased rate of glycolysis induced by the uncoupler corresponds to an increased rate of the conversion of free hexoses and polysaccarides to hexose phosphates. In yeast about 30% of the radioactivity supplied and taken up as ¹⁴C labelled glucose, and 20% of that supplied and taken up as glycerol is recovered as soluble sugar and glycogen; this phenomenon is almost completely suppressed by 10^-4M DNP.

This suggested that a mechanism involving kinase enzymes, on one hand, and phosphatases, on the other, is mediating the interconversion of phosphorylathed and free sugars, and that the apparent increase of hexose phosphorylation observed in the presence of DNP might depend on a decreased rate of phosphatase mediate reactions, consequent to the decrease of phosphorylated sugars level in the cell.

The experiments here reported were planned to test the validity of this hypothesis in the case of higher plant tissues.

Material used in these experiments were segments from the growing part of the third internode isolated from 7 day old, etiolated pea seedlings, and carrot root diks (0,7 mm thick, 7 mm diameter) preincubated for 24 hours in aerated distilled water. Both of these materials show an active, steady respiration and some growth activity, so that they may be taken as representing a condition close enough to that of the generally physiologically active higher plant tissues.

The reversibility of the hexose phosphate-free sugar interconversion process was tested by feeding 10^-3M 1-C¹⁴ labeled glycerol, and measuring after 150 minutes the amount of radioactivity incorporated into CO₂, soluble sugars, organic acids and proteins. The results of these experiments are summarized in table I and II.

Glycerol metabolism as well as its response to DNP appears very similar in the two material used. In both cases, glycerol uptake and incorporation into organic acids and amino acids is almost insensitive to DNP. In contrast large differences are observed for the free sugar fraction. In the absence of the uncoupler, a consistent amount of the radioactivity fed as glycerol is found in this fraction. It appears reasonable to assume that the glycerol-sugar interconversion comprehends, as intermediate steps, glycerol-P, fructose di-P (or sedoeptulose di-P) and hexose-6-P. If this is true, the observed data implicate that a continuous interconversion occurs, in the cell, between sugar phosphates and free sugars and vice-versa, one reaction direction involving the activity of phosphatases, and the other one that of kinases. The true rate of this interconversion process is probably much larger than indicated by the radioactivity found in free sugars: as a considerable part of the triose-P transormed into sugars must immediately re-enter the descending flux of glycolysis.

This view finds some support in the fact that DNP almost completely inhibits the incorporation of radioactivity in the free sugar fraction. It has been previously observed that DNP very markedly decreases the level of hexose mono- and di-phosphates and of triose-phosphates in the pea stem tissues. If phosphatases acting on fructose di-phosphate and on hexose-6-P are not saturated by their substrates, a decrease of the rate of free hexose synthesis from sugar phosphates should be expected.

The present results are thus consistent with the hypothesis that hexose phosphates and free sugars in the cell are continuously interconverted by the simultaneous action of phosphatases and kinases; and that the effect of DNP, and thus of any physiological conditions decreasing the ATP/ADP ratio in accelerating free hexose utilizations is at least in part due to a decreased rate of the reactions catalized by fructose diphosphate and hexose-6-P phosphatases. The reversibility of the kinase-phosphatase system would thus represent a crucial link in the mechanism by which the rate of carbohydrate activation and breackdown is controlled by the rate of utilization of high-energy phosphate bonds.     

Azione Esercitata Da Alcuni Inibitori Respiratori Sull'Inverdimento Di Apici Caulinari Di Piantine Eziolate Di Pisello

Abstract

Action of some respiratory inhibitors on the greening of apices of etiolated pea. — Aim of the research is to study the effect of some of the best kown respiratory inhibitors on the greening of etiolated apices of peas excised from the plant and kept in light in solutions containing saccharose. The inhibitors studied may act on more than one of the reactions leading to the synthesis of the chlorophyll molecule.

The following can be concluded from the present study:

1. A good level of chemical energy seems to be necessary for greening.

2. Terminal iron-oxidases seem to be necessary in this process, while a stimulating effect on greening may be attributed to an inhibition of the terminal copper-oxidases (particularly ascorbic-oxidase); the effect can be explained with the hormonal control of greening by the indoleacetic/ascorbic system.

3. Enzymes of the Krebs cycle regulate both the uptake of the essential metabolites starting from the chlorophyll molecule and the production of chemical energy.

4. Some enzymes of the glycolysis take part in some of the reactions leading to the synthesis of the chlorophyll molecule.     

An in vivo analysis of the effect of SO2 fumigation on photosynthesis in Zea mays.

Fumigation of leaves with SO₂ can reduce the capacity for photosynthetic CO₂ uptake even in the absence of visible symptoms of damage. In vitro studies suggest that this invisible injury to intact leaves could be affected by damage to each of the main stages in the photosynthetic process. Reduced stomatal apertures may also reduce photosynthesis following SO₂ fumigation. The responses of CO₂ uptake by leaves to intercellular CO₂ concentration and to absorbed light provide information for quantitative separation of the in vivo contribution of the different stages of photosynthesis to reduction in overall rate. This study uses these techniques to examine the basis of reduction in CO₂ uptake in Zea mays cv. LG11 leaves following short-term fumigation with SO₂. Fumigation with 33 μmol m^–3 SO₂ for 30 min reduced light saturated CO₂ uptake by about one-third. An even greater reduction in light limited CO₂ uptake was observed and with no significant change in light absorptance this was attributed to a reduced quantum yield of photosynthesis. The light saturated CO₂ uptake rate and the stomatal conductance decreased in parallel. However, the relationship of CO₂ uptake to the intercellular CO₂ concentration suggested that the reduced stomatal conductance did not account for the reduced rate of CO₂ uptake following fumigation. Both the initial slope and plateau of this relationship were significantly reduced, suggesting that both carboxylation efficiency and capacity for regeneration of CO₂ acceptor were diminished by SO₂ fumigation. The operating intercellular CO₂ concentration indicated that both processes were co-limiting, before and after fumigation. The time required for induction of photosynthetic CO₂ uptake on illumination was approximately doubled following SO₂ fumigation, showing that fumigation impairs the ability of the photosynthetic apparatus to adapt to fluctuations in light level.     

Reduced stomatal responses to light, carbon dioxide and abscisic acid in the presence of sodium ions

Abstract Responses of stomata to light and CO₂ were smaller when detached epidermis of Commelina communis L. was incubated on a medium containing 50 mol m^?3 NaCl than when an equimolar KCl solution was used. Although opening in the light in the absence of CO₂ seemed to be the same whichever salt was present, apertures on KCl solutions were smaller in the dark or with CO₂-containing air. The response to 10^?7 mol dm^?3 ABA was similarly reduced in the presence of NaCl. If there is an optimal NaCl concentration for stomatal CO₂ and light responses it is at or below 25 mol m^?3. These findings point towards control of stomatal movements by light, CO₂ and ABA at the level of cation uptake or extrusion.     

Oxygen and carbon dioxide exchanges in crassulacean-acid-metabolism-plants

The 24 h O₂ uptake and release together with the CO₂ balance have been measured in two CAM plants, one a non-succulent Sempervivum grandifolium, the other a succulent Prenia sladeniana. The O₂ uptake was estimated by the use of ¹⁸O₂. It was found that the mean hourly O₂ uptake in the light was 7 times that in the dark for Sempervivum and 5 times that for Prenia, after correction for the lightdark temperature difference. It was estimated that oxygen uptake in the light was 2.4 times greater than oxygen release (=net photosynthesis) in Sempervivum and 1.4 times greater in Prenia. In both plants there was a positive carbon balance over the 24 h period under the experimental conditions. It was estimated that malate formed during the night could, if completely oxidized to CO₂ and water, account for 74% of the light phase O₂ uptake in Sempervivum. In Prenia the O₂ uptake was more than sufficient to account for a full oxidation of malate.Abbreviations CAM Crassulacean acid metabolism - PAR photosynthetically active radiation - PEP phosphoenolpyruvate - RrBP ribulose-1,5-bisphosphate - TCA tricarboxylic acid cycle     

Light-dependent bicarbonate uptake and CO2 efflux in the marine microalga Nannochloropsis gaditana

 Inorganic carbon (Ci) uptake and efflux has been investigated in the marine microalga Nannochloropsis gaditana Lubian by monitoring CO₂ fluxes in cell suspensions using mass spectrometry. Addition of H¹³CO₃ ⁻ to cell suspensions in the dark caused a transient increase in the CO₂ concentration in the medium far in excess of the equilibrium CO₂ concentration. The magnitude of this release was dependent on the length of time the cells had been kept in the dark. Once equilibrium between the Ci species had been achieved, a CO₂ efflux was observed after saturating light intensity was applied to the cells. External carbonic anhydrase (CA) was not detected nor does this species demonstrate a capacity to take up CO₂ by active transport. Photosynthetic O₂ evolution and the release CO₂ in the dark depend on HCO₃ ⁻ uptake since both were inhibited by the anion exchange inhibitor, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS). The bicarbonate uptake mechanism requires light but can also continue for short periods in the dark. Ethoxyzolamide, a CA inhibitor, markedly inhibited CO₂ efflux in the dark, indicating that CO₂ efflux was dependent upon the intracellular dehydration of HCO₃ ⁻. These results indicate that Nannochloropsis possesses a bicarbonate uptake system which causes the accumulation of high intracellular Ci levels and an internal CA which maintains the equilibrium between CO₂ and HCO₃ ⁻ and thus causes a subsequent release of CO₂ to the external medium. Received: 20 September 1999 / Accepted: 25 October 1999     

Fissazione di CO2 in Cuscuta epithymum

Abstract

CO₂ FIXATION IN CUSCUTA EPITHYMUM. — Seedlings of Cuscuta epithymum fixe approximately the same amount of C¹⁴O₂ irrespectively of age, pigmentation, presence or absence of light. Examination by paper chromatography of the extracts of plants exposed to C¹¹O₂ revealed that most, or all, of the radioactivity is concentrated in the area of the organic acids and of the acidic amino acids. It is tentatively concluded that C. epithymum fixes carbon dioxide through a mechanism different from that involving ribulose-1,5-diphosphate carboxylase and carboxydismutase.     

Sul Controllo Della Glicolisi Nel Lievito

Abstract

On the control of carbohydrate utilization in yeast. — The results of a previous investigation showed that in higher plants the stimulating action of 2,4 dinitrophenol (DNP) on oxygen uptake and glycolysis is accompained by a fall of the level of reducing sugars, due to an increase of their respiratory utilization, and thus — according to every evidence — of the rate of hexose phosphate synthesis.

In the present work, the occurrence of a similar phenomenon in yeast (where the inhibiting effect of DNP on glucose uptake is not so much marked as in higher plant tissue) was investigated.

Here again DNP, at a 10^-4M concentration, induced a rapid decrease of the disaccaride trehalose and of glycogen, such as to account for the increased rate of respiration and of fermentation. The ratio between the contributions to CO₂ of Carbons 1 and respectively 6 of glucose was not significantly changed by DNP, which suggests that at least part of the DNP induced increase of glycolysis was mediated by the Embden Meyerhof pathway, and thus that a larger amount of fructose diphosphate was formed in the presence of the uncoupler.

In other experiments the effects of DNP on the dissimilation of C¹⁴ labeled glucose, glycerol and pyruvate to CO₂ and ethanol, and on the incorporation of the radioactive isotope into various fractions, 15 minutes after feeding the labeled substrates, was investigated. It was found that:

1) Glucose and glycerol uptake is not markedly inhibited by DNP at the concentration employed (^10–4M).

2) In the absence of DNP, a considerable portion of the radioactivity fed as glucose or glycerol and taken up by the yeast cells is recovered in the glycogen and trehalose fractions. (35% of the glucose, and 22% of the glycerol taken up). This is also observed for carbons 2 and 3, but not for carbon 1 of pyruvate. This indicates a reversibility of the glycolitic processes comprehended in the region between phospho-enol pyruvate andpolysac-carides; while the pyruvate kinase reaction appears to represent a sharp barrier at the « lower » end of glycolysis.

3) DNP almost completely inhibited the incorporation of C¹⁴ from glucose and glycerol into glycogen and trehalose, although it increased the rate of its dissimilation to CO₂ and ethanol. The total amount of glucose and glycerol transformed in the various metabolites (and thus — according to every evidence — phosphorylated) was somewhat lowered and proteins synthesis severely depressed. These effects are interpreted as due to the uncoupling action of DNP at the mitochondrial level, and to the consequent general decrease of the ATP and UTP levels required for protein and for polysaccharide synthesis.     

The Influence of Photosynthetic Factors and Metaholic Inhibitors on the Uptake of Phosphate in P-Deficient Scenedesmus

The cells used in the present investigation had a phosphate content of about 20 per cent as compared with the status in normal cultures. The uptake of phosphate during a period of 4 hours was determined at a pH of 6,5, kept constant with the aid of a citrate buffer. In the absence of CO₂, light increased the uptake of phosphate with saturation around 14,000 erg/cm²s. With 5 per cent CO₂ in the air the relationship was more complicated, and the uptake of phosphate must he related to more than one process during active photosynthesis. The inhibiting effect of CO₂ in air was noticeable already at low concentrations both in light and in darkness. With the system used, this supports earlier indications for internal recycling of orthophosphate, CO₂ was inhibiting also in nitrogen in the light. Selenate in a concentration of 2 mM gave a slight and rather irregular inhibition.—Anaerobiosis had no effect in the light but gave a large decrease in the dark.—DNP (0.1 mM) was somewhat more active in the dark than in the light. The lower concentrations tested had no effect in either case.—Menadione (0.1 mM) inhibited strongly, and more in illuminated than in non-illuminated cells.     

Reversible inactivation of nitrate reductase in Chlorella vulgaris in vivo

Summary The NADH-nitrate oxidoreductase of Chlorella vulgaris has an inactive form which has previously been shown to be a cyanide complex of the reduced enzyme. This inactive enzyme can be reactivated by treatment with ferricyanide in vitro. In the present study, the activation state of the enzyme was determined after different prior in vivo programs involving environmental variations. Oxygen, nitrate, light and CO₂ all affect the in vivo inactivation of the enzyme in an interdependent manner. In general, the inactivation is stimulated by O₂ and inhibited by nitrate and CO₂. Light may stimulate or inhibit, depending on conditions. Thus, the effects of CO₂ and nitrate (inhibition of reversible inactivation) are clearly manifested only in the light. In contrast, light stimulates the inactivation in the presence of oxygen and the absence of CO₂ and nitrate. Since the inactivation of the enzyme requires HCN and NADH, and it is improbable that O₂ stimulates NADH formation, it is reasonable to conclude that HCN is formed as the result of an oxidation reaction (which is stimulated by light). The formation of HCN is probably stimulated by Mn²⁺, since the formation of reversibly-inactivated enzyme is impaired in Mn²⁺-deficient cells. The prevention of enzyme inactivation by nitrate in vivo is in keeping with previous in vitro results showing that nitrate prevents inactivation by maintaining the enzyme in the oxidized form. A stimulation of nitrate uptake by CO₂ and light could account for the effect of CO₂ (prevention of inactivation) which is seen mainly in the presence of nitrate and light. Ammonia added in the presence of nitrate has the same effect on the enzyme as removing nitrate (promotion of reversible inactivation). Ammonia added in the absence of nitrate has little extra effect. It is therefore likely that ammonia acts by preventing nitrate uptake. The uncoupler, carbonylcyanide-m-chloro-phenylhydrazone, causes enzyme inactivation because it acts as a good HCN precursor, particularly in the light. Nitrite, arsenate and dinitrophenol cause an enzyme inactivation which can not be reversed by ferricyanide in crude extracts. This suggests that there are at least two different ways in which the enzyme can be inactivated rather rapidly in vivo.     

Autotrophe Gewebekulturen von Ruta graveolens und deren 14CO2-Markierungsprodukte

Summary It is possible to obtain autotrophic callus cultures by inhibiting cell respiration. During a first passage of four weeks the cultures synthesized chlorophyll on an agar-medium with a minimum of organic substances such as sugar, amino acids and vitamins. In the second passage these cultures were kept on the same medium but were aerated with a mixture of 99% N₂ and 1% CO₂. In the third and last passage the medium contained only mineral substances and the same mixture of N₂ and CO₂ was used for aeration. This pure mineral medium was supplemented with the Hoagland's solution.These autotrophic callus cultures were grown for about two years under these conditions and showed a growth quotient of ten.Three different groups of tissues were taken for the ¹⁴CO₂-fixation. The first group was grown for four weeks on a heterotrophic medium and aerated with O₂. This is the socalled respirating group. The second and third group were both aerated with the mixture of N₂/CO₂ but they were grown on different mediums. One of these groups was grown on a heterotrophic medium for four weeks: these are heterotrophic photosynthesizing tissues. The third group was grown on a pure mineral medium, and these are the autotrophic photosynthesizing callus tissues.Respirating tissues are different from photosynthesizing cultures in respect to the quantity of light-induced CO₂-fixation.The thin-layer chromatograms reveal the difference between heterotrophic and autotrophic tissues. In the light dependent ¹⁴CO₂-incorporation the difference is in the amounts of the labelled amino acids glycine and serine. In the dark dependent incorporation the difference is found in the amount of the labelled amino acid aspartic acid. The more autotrophic these tissues are, the higher the level of the CO₂-fixation in these amino acids is.

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Mit Hilfe der Deutschen Forschungsgemeinschaft.     

Influence of enhanced CO2 on growth and photosynthesis of the red algaeGracilaria sp. andG. chilensis

The influence of elevated CO₂ concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO₂. Growth of both was enhanced by CO₂ enrichment (air + 650 ppm CO₂, air + 1250 ppm CO₂, the enhancement being greater inGracilaria sp. Both species increased uptake of NO₃ ^– with CO₂ enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO₂ enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O₂ uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO₂ in culture.     

Invasive submerged freshwater macrophytes are more plastic in their response to light intensity than to the availability of free CO2 in air‐equilibrated water

相似文献   

Photosynthetic energy supply for NO3− assimilation in Scenedesmus

NO₃^?-dependent O₂ in synchronous Scenedesmus obtusiusculus Chod. in the absence of CO₂ is stoichiometric with NH₄⁺ excretion, indicating a close coupling of NO₃^? reduction to non-cyclic electron flow. Also in the presence of CO₂, NO₃^? stimulates O₂ evolution as manifested by an increase in the O₂/CO₂ ratio from 0.96 to 1.11. This quotient was increased to 1.36 by addition of NO₂^?, without competitive interaction with CO₂ fixation, indicating that the capacity for non-cyclic electron transport at saturating light is non-limiting for simultaneous reduction of NO₃^? and CO₂ at high rates. During incubation with NO₃^?+ CO₂, no NH₄⁺ is released to the outer medium, whereas during incubation with NO₂^?+ CO₂, excess NH₄⁺ is formed and excreted. NO₃^? uptake is stimulated by CO₂, and this stimulation is also significant when the cellular energy metabolism is restricted by moderate concentrations of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone, whereas NO₃^? uptake in the absence of CO₂ is severely inhibited by the uncoupler. Also under energy-restricted conditions NO₃^? uptake is not competitive with CO₂ fixation. Antimycin A is inhibitory for NO₃^? uptake in the absence of CO₂, and there is no enhancement of NO₃^? uptake by CO₂ in the presence of antimycin A. It is assumed that the energy demand for NO₃^? uptake is met by energy fixed as triosephosphates in the Calvin cycle. Antimycin A possibly affects the transfer of reduced triose phosphates from the chloroplast to the cytoplasm. Active carbon metabolism also seems to exert a control effect on NO₃^? assimilation, inducing complete incorporation of all NO₃^? taken up into amino acids. This control effect is not functional when NO₂^? is the nitrogen source. Active carbon metabolism thus seems to be essential both for provision of energy for NO₃^? uptake and for regulation of the process.     

Refixation of xylem sap CO2 in Populus deltoides

Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO₂ in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO₂ to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO₂ in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of three Populus deltoides trees had mean dissolved inorganic carbon concentrations (CO₂+H₂CO₃+HCO^?₃) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[¹⁴C]NaHCO₃, 99. 6% of the label was fixed in the light. Seventy-seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue in P. deltoides leaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO₂ delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO₂ uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[¹⁴C]CO₂. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5-s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO₂ delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C-3 photosynthesis.     

Zur Wirkung von Sauerstoff auf die 32P-Markierung von Polyphosphaten und organischen Phosphaten bei Ankistrodesmus braunii im Licht

Summary Short time incorporation of ³²P was carried out with synchronised algae (young cells) depleted of phosphate. For the separation and determination of the acid-insoluble phosphate fractions of the cells an improved fractionation procedure was applied. In order to exclude competition by carbon dioxide all experiments were done in the absence of CO₂.Compared with nitrogen, CO₂-free air produces an increase in the labelling of phosphorylated compounds in the light. In strong white light, at high pH, air effects a remarkable increase of ³²P in the acid-insoluble phosphate (P _u), mainly in inorganic polyphosphates (P _ul), whereas the total phosphate uptake remains almost unchanged. The increase in labelling of acid-insoluble phosphate is, therefore, accompanied by a substantial decrease in the labelling of acid-soluble compounds (P _l). In weak white light or in far-red light, at low pH even in strong white or red light, an increase of phosphate uptake and an increased labelling of the acid-stable organic acid-soluble fraction (P _os) is observed instead. The effect of oxygen increases somewhat with increasing light intensity up to light saturation, and it increases markedly with increasing oxygen concentration.An essential contribution by oxidative phosphorylation to this oxygen effect can be ruled out on account of its much higher sensitivity to oxygen. Pseudocyclic photophosphorylation is also not regarded as the main force because of its higher oxygen affinity. Occurrence of photorespiration has not been clearly established so far in related algae (Chlorella), and its use for phosphorylation is unknown. A better, although not complete explanation is given by comparing the oxygen effect with the well-known inhibition of photosynthesis by oxygen (Warburg effect), which leads to an increase in glycolate formation and a simultaneous decrease in the pool sizes of carbon reduction cycle intermediates, even in the absence of CO₂. Since the photophosphorylation process, as well as the photosynthetic electron flow, seem unaffected by high oxygen concentrations whereas the formation of organic phosphate compounds is partially inhibited, excess ATP may be available for polyphosphate synthesis. This explanation would be consistent with the assumption that polyphosphate-ADP kinase mediates an equilibrium between ATP and polyphosphates, mainly at higher pH. At low pH and in other cases the excess ATP might be available for an increased phosphate uptake and for phosphorylation of endogenous carbohydrates.

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Herrn Prof. Dr. W. Simonis zum 60. Geburtstag gewidmet.     

Photosynthetic inorganic carbon uptake and accumulation in two marine diatoms

Some physiological characteristics of photosynthetic inorganic carbon uptake have been examined in the marine diatoms Phaeodactylum tricornutum and Cyclotella sp. Both species demonstrated a high affinity for inorganic carbon in photosynthesis at pH7.5, having K_1/2(CO₂) in the range 1.0 to 4.0mmol m^?3 and O_2? and temperature-insensitive CO₂ compensation concentrations in the range 10.8 to 17.6 cm³ m^?3. Intracellular accumulation of inorganic carbon was found to occur in the light; at an external pH of 7.5 the concentration in P. tricornutum was twice, and that in Cyclotella 3.5 times, the concentration in the suspending medium. Carbonic anhydrase (CA) was detected in intact Cyclotella cells but not in P. tricornutum, although internal CA was detected in both species. The rates of photosynthesis at pH 8.0 of P. tricornutum cells and Cyclotella cells treated with 0.1 mol m^?3 acetazolamide, a CA inhibitor, were 1.5- to 5-fold the rate of CO₂ supply, indicating that both species have the capacity to take up HCO₃^? as a source of substrate for photosynthesis. No Na⁺ dependence for HCO₃^? could be detected in either species. These results indicate that these two marine diatoms have the capacity to accumulate inorganic carbon in the light as a consequence, in part, of the active uptake of bicarbonate.     

Untersuchungen über die Aufnahme von Glykolat bei Chlorogonium

Summary The alga Chlorogonium was cultured either heterotrophically or autotrophically under different partial pressures of CO₂ by aerating with pure air of air enriched with 2% CO₂. Cells were harvested in the logarithmic phase, transferred to phosphate buffer containing 0.01 M 1C¹⁴-glycolate and incubated with shaking in the dark. Under these conditions the rate of glycolate uptake was higher when the cells had been grown in the light. Cells grown in the light at the lower CO₂-concentration took up more glycolate than those grown with 2% CO₂. Approximately 90% of the radioactivity taken up with the glycolate was released as CO₂. The radioactivity remaining in the algae was somewhat higher in those cells which had been cultured heterotrophically or autotrophically under air than in cells grown autotrophically under air enriched with 2% CO₂.Addition of glycolate increased the uptake of oxygen by the cells. The consumption of the oxygen was quantitatively correlated to the uptake of glycolate.