Wolfgang Wiessner

Evidence of de novo synthesis of maltose excreted by the endosymbiotic Chlorella from Paramecium bursaria.

The endosymbiotic Chlorella sp. from Paramecium bursaria excretes maltose both in the light and in the dark. Experiments on photosynthetic 14CO2 fixation and 14CO2 pulse-chase experiments show that maltose is synthesized in the light directly from compounds of the Calvin cycle, whereas in the dark it results from starch degradation.

Enzymaktivität und Kohlenstoffassimilation bei Grünalgen unterschiedlichen ernährungsphysiologischen Typs

In several algae (Chlamydobotrys stellata, Chlamydomonas mundana, Chlorella vulgaris, Chlorogonium elongatum, Euglena gracilis, Scenedesmus obliquus) the influence of the nutrition either with carbon dioxide or with acetate on the activities of enzymes typical for the Calvin- or the glyoxylate-cycle has been studied. The activities of the NADP-glyceraldehyde-dehydrogenase and the Ls-isocitrate-lyase were compared with the actual role of indirect (via photosynthetic assimilation of carbon dioxide released from acetate by oxydation) and direct (via the glyoxylatecycle) photo-assimilation of carbon from acetate in the light dependent synthesis of carbohydrates. From the results obtained during this investigation it can be concluded that which pathway of carbon from acetate to carbohydrates predominates in the light depends mainly on the autotrophic or photoheterotrophic nature of the organisms, in spite of the fact that in algae of the autotrophic type the nutrition with acetate also induces the activity of enzymes necessary for the direct assimilation of acetate.SummaryIn several algae (Chlamydobotrys stellata, Chlamydomonas mundana, Chlorella vulgaris, Chlorogonium elongatum, Euglena gracilis, Scenedesmus obliquus) the influence of the nutrition either with carbon dioxide or with acetate on the activities of enzymes typical for the Calvin- or the glyoxylate-cycle has been studied. The activities of the NADP-glyceraldehyde-dehydrogenase and the Ls-isocitrate-lyase were compared with the actual role of indirect (via photosynthetic assimilation of carbon dioxide released from acetate by oxydation) and direct (via the glyoxylatecycle) photo-assimilation of carbon from acetate in the light dependent synthesis of carbohydrates. From the results obtained during this investigation it can be concluded that which pathway of carbon from acetate to carbohydrates predominates in the light depends mainly on the autotrophic or photoheterotrophic nature of the organisms, in spite of the fact that in algae of the autotrophic type the nutrition with acetate also induces the activity of enzymes necessary for the direct assimilation of acetate.

Short- and long-term redox regulation of photosynthetic light energy distribution and photosystem stoichiometry by acetate metabolism in the green alga, Chlamydobotrys stellata

The effect of acetate metabolism on the light energy distribution between the two photosystems, on the PS II/PS I stoichiometry and on the expression of psbA and psbB and psaA genes was investigated in the green alga, Chlamydobotrys stellata during autotrophic (CO2), mixotrophic (CO2 plus acetate) and photoheterotrophic (only acetate) cultivation. It was observed that acetate assimilation in the glyoxylate cycle resulted in a large drop in the ATP content and a concomitant increase in the NADPH content of the cells. The combined effect of high NADPH concentration and linear electron transport brought about an over-reduction of the inter-photosystem electron transport components. The reduced state of the inter-photosystem components initiated a state 1/state 2 transition of LHC II and a decrease in the PS II/PS I ratio. The PS II/ PS I ratio was reduced because the synthesis of PS II reaction centers was repressed and that of the PS I reaction centers was slightly enhanced by acetate cultivation. The amount of PsbA and PsbB proteins of PS II and the abundance of psbA mRNA decreased. The abundance of PS I PsaA protein and psaAmRNA were only slightly increased. All of the acetate-induced effects were reversible when the cells were transferred back to an acetate-free medium. Our observations demonstrate that the expression of the PS II psbA and psbB and PS I psaA genes is regulated by the redox state of the inter-photosystem components at the transcriptional level. Experiments carried out in the presence of DBMIB which facilitates the reduction of plastoquinone pool indicate that the expression of genes encoding the components of PS II and PS I are controlled by the redox state of a component (cytochrome b/f complex) located behind the plastoquinone pool.

Effects of in vivo CO2-depletion on electron transport and photoinhibition in the green algae, Chlamydobotrys stellata and Chlamydomonas reinhardtii

Abstract Short-term illumination of the green algae, Chlamydobotrys stellata and Chlamydomonas reinhardtii in CO2-depleted cultivation medium under low photon flux density (50 and 150 μmol m−2 s−1, respectively) resulted in an inhibition of Photosystem II electron transport from water to diaminodurene, but only slightly affected the electron flow from water to 2,6-dichlorobenzoquinone. The intermediary fluorescence level, Fi was raised to the maximum level of fluorescence, Fm. The initial level of fluorescence, Fo was considerably enhanced. The development of the Fo rise was facilitated by low pH, but inhibited in the presence of an acceptor, dichlorobenzoquinone, or by chemical cross-linking of proteins with glutaraldehyde. The uninhibited electron transport and the original Fo level were restored by readdition of CO2 or by dark adaptation of algae. The observations suggest that in green alga cells CO2-depletion in the light results in a reversible inhibition of steady-state electron flow between the primary (QA) and secondary quinone electron acceptor (QB). Following the inhibition of electron transport a long-lived but reversible state of singly-reduced and probably protonated QA is formed which manifests itself as an apparent Fo rise. Prolonged photoinhibitory illumination of the CO2-depleted green alga cells resulted in an irreversible loss of variable fluorescence and electron transport. The photoinactivation developed more slowly in the CO2-depleted than in the CO2-containing cells. It is concluded that in the bicarbonate-depleted redox state, which is accompanied with an enhanced Fo level of fluorescence, the Photosystem II reaction center is less susceptible to photoinhibition than in the bicarbonate-containing state.

Ernhrung und Stoffwechsel von Chlamydobotrys (Volvocales)

Zusammenfassung1.Chlamydobotrys wächst in Reinkultur nur im Licht und nur mit Acetat als organischer Kohlenstoffquelle.2.Eine Photoassimilation von Acetat ist der grundlegende Prozeß für den Aufbaustoffwechsel.3.Die Photosynthese ist, verglichen mit anderen Grünalgen (Chlorella, Chlorogonium), nur schwach.4.Begasung mit Kohlendioxyd führt zwar zu einer Anhäufung von Kohlenhydraten in der Zelle, doch nur zu einer sehr geringfügigen Vermehrung der stickstoffhaltigen Verbindungen, die zu einem Wachstum nicht ausreicht. Die Synthese von Protein findet vorwiegend aus Acetat statt; anorganische Stickstoffquellen (Ammon, Nitrat) können verwertet werden; aber mit Asparagin oder Asparaginsäure ist die Vermehrung weit reichlicher.5.Die endogene Atmung von Chlamydobotrys ist ebenso hoch wie bei anderen Grünalgen (Chlorella, Chlorogonium). Durch Zufuhr von Acetat kann sie aber nur wenig, durch Zugabe von Glucose gar nicht gesteigert werden. Im Dunkeln wird nur ganz wenig Acetat und in der Zelle gespeichertes Reservekohlenhydrat in Protein umgewandelt.

The role of endosymbiotic algae in photoaccumulation of green Paramecium bursaria

The endosymbiotic unit of Paramecium bursaria with Chlorella sp. photoaccumulates in white, blue-green, and red light (λ<700 nm), whereas alga-free Paramecia never do. The intensity of photoaccumulation depends on both the light fluence rate and the size of the symbiotic algal population. Photoaccumulation can be stopped completely with 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthetic electron transport. Hence the photosynthetic pigments of the algae act as receptors of the light stimulus for photomovement and a close connection must exist between photosynthesis of the algae and ciliary beating of the Paramecium.

Unterschiedliche Temperaturoptima der DNA-abhängigenRNA-Polymerasen von Euglena gracilis, Stamm Z und ihre Bedeutung fur die experimentelle Erzeugung der permanenten Apochlorose durch höhere Temperatur

Summary The DNA-dependent RNA-Polymerases I, II, III and IV were isolated from Euglenagracilis, strain Z, identified and tested for their activity in the temperature range between 25 and 35 °C. Optimum temperature for the nuclear RNA-polymerases I, II and III is 32–33 °C. At 28 °C the activity of these enzymes has decreased to about 20 %. At 34–35 °C still 15 %, respectively 40 0% and 20 %o of the optimal activity of these three RNA-polymerases is present. In contrast to the behaviour of the nuclear RNA-polymerases the optimum temperature for the plastidial RNA-polymerase is 28-29 °C. Its activity at 34–35 °C is about zero. Thus the application of 34–35 °C in the temperature sensitive section of the cell cycle of Euglena gracilis inhibits the activity of the plastidial RNA-polymerase and thus leads to permanent apochlorosis. It has been demonstrated in addition that the activity of the plastidial RNA-polymerase of the strain V of Euglena gracilis, which cannot be bleached by application of high temperature, is decreased at 34–35 °C to only about 35 % of its optimum activity.

Photobehaviour of Paramecium bursaria infected with different symbiotic and aposymbiotic species of Chlorella

The endosymbiotic unit of Paramecium bursaria and Chlorella spec. shows two types of photobehaviour: 1) A step-up photophobic response which possibly depends on photosensitive agents in the ciliate cell itself — as is also shown by alga-free Paramecium bursaria - and can be drastically enhanced by photosynthetic activity of symbiotic algae; and 2) a step-down photophobic response. The step-down response leads to photoaccumulation of green paramecia. Both types of photobehaviour in Paramecium bursaria do not depend on any special kind of algal partners: The infection of alga-free Paramecium bursaria with different Chlorella species results in new ciliatealgae-associations. They are formed not only by combination of the original symbiotic algae with their host, but also by infection with other symbiotic or free-living (aposymbiotic) chlorellae, respecitively. Systems with other than the original algae are not permanently stable — algae are lost under stress conditions — but show the same types of photobehaviour. Photoaccumulation in general requires algal photosynthesis and occurs only with ciliates containing more than fifty algae/cell. It is not mediated by a chemotactic response to oxygen in the medium, since it occurs at light fluence rates not sufficient for a release of oxygen by the symbiotic system, e.g., below its photosynthetic compensation point. Photoresponses can be inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU). Sensory transduction does not depend on any special symbiotic features of the algae, e.g., sugar excretion. The participation of oxygen in the Paramecium cell, of its cytoplasmic pH and of ions released or taken up by endosymbiotic algae in sensory transduction is discussed.

Stoffwechselleistung und Enzymaktivität bei Chlamydobotrys (Volvocales)

In Versuchen mit Chlamydobotrys, dessen Stoffwechsel vor allem von der Photoassimilation von Acetat abhangt, konnte gezeigt werden, das Anderungen der Leistung bei der Photoassimilation von Acetat und dessen oxydativem Dunkel-Stoffwechsel von ahnlichen Anderungen der Aktivitat gewisser Enzyme begleitet sind. Wahrend des optimalen Wachstums des Organismus auf Acetat ist die Fahigkeit zur Photoassimilation von CO2 sehr gering, was mit einer niedrigen Aldolaseaktivitat einhergeht. Nach Ubertragung der Algen auf ein acetatfreies Medium nehmen Photoassimilation von CO2 und Aldolaseaktivitat zu. Eine maximale Aldolaseaktivitat konnte nur erzielt werden, wenn eine Stickstoffquelle (NH4Cl) die Synthese von aktivem Enzymprotein ermoglicht.ZusammenfassungIn Versuchen mit Chlamydobotrys, dessen Stoffwechsel vor allem von der Photoassimilation von Acetat abhängt, konnte gezeigt werden, daß Änderungen der Leistung bei der Photoassimilation von Acetat und dessen oxydativem Dunkel-Stoffwechsel von ähnlichen Änderungen der Aktivität gewisser Enzyme begleitet sind. Während des optimalen Wachstums des Organismus auf Acetat ist die Fähigkeit zur Photoassimilation von CO2 sehr gering, was mit einer niedrigen Aldolaseaktivität einhergeht. Nach Übertragung der Algen auf ein acetatfreies Medium nehmen Photoassimilation von CO2 und Aldolaseaktivität zu. Eine maximale Aldolaseaktivität konnte nur erzielt werden, wenn eine Stickstoffquelle (NH4Cl) die Synthese von aktivem Enzymprotein ermöglicht.SummaryIn experiments with Chlamydobotrys, the metabolism of which depends mainly on the photoassimilation of acetate, changes in the metabolic activity for the photoassimilation of acetate and its oxidative dark-metabolism could be shown to be accompanied by similar changes in the activity of certain enzymes. During optimal growth of the organism on acetate the ability for photoassimilation of CO2 is extremely weak which is corresponded by low aldolase-activity. After transferance of the algae to an acetatefree medium the photoassimilation of CO2 and the aldolase-activity rise. Maximum aldolase-activity could only be obtained, if a nitrogen-source (NH4Cl) makes possible a synthesis of active enzyme-protein.

Infection of algae-free Paramecium bursaria with symbiotic Chlorella sp. Isolated from green paramecia: I. Effect of the incubation period.

The significance of the length of incubation (30 sec to 48 h) of algae-free Paramecium bursaria with symbiotic Chlorella sp. for the success of infection, i.e. the reestablishment of the endosymbiotic algae has been investigated. When algae are brought together with paramecia, they are rapidly taken up by the ciliates. During a 30 sec incubation one ciliate engulfs about 50 chlorellae. A prolongation of the incubation period increases the number of ingested algae. However, the success of infection, determined one and five day(s) after the end of the incubation, is independent from the length of the incubation period and, consequently, does not depend on the number of ingested algae, either: In all experiments about 50% of the Paramecium population becomes infected and one to three algae are primarily enclosed in individual perialgal vacuoles within a ciliate cell. Thus, the endosymbiont population of a Paramecium cell originates on an average from two algae. Since successful infection is restricted only to a part of the Paramecium population and since the number of primarily established endosymbionts does not depend on the number of ingested algae, the success of infection and the formation of perialgal vacuoles seem to be not limited by properties of the algae but by features of the host, the possible nature of which is discussed.