Harald Lorenzen

Nitrate uptake and nitrate reduction in synchronous Chlorella

Nitrate uptake was followed continuously in cultures of Chlorella sorokiniana using ionsensitive electrodes. During the lifecycle of the synchronous cell cultures, a drastic increase occurred in the first hour after the onset of the light. Nitrate uptake rate was shown to be dependent on illumination intensity, nitrate concentration, and temperature. These results point to an energy-linked uptake process. From the different timecourses of nitrate uptake rate and nitrate reductase activation, one can conclude that the increased nitrate reductase activity after light onset is regulated via nitrate uptake. Further evidence for a regulation in this direction is shown by the action of ammonium on nitrate uptake and nitrate reductase activity. The results are discussed in terms of the regulation of the nitrate consuming system.

Versuche zur Gliederung des Entwicklungsverlaufs derChlorella-Zelle

Zusammenfassung1.Bei komplett synchronisierten Kulturen (Licht-Dunkel-Wechsel 16:12 Std, 30°C, 9000 Lux und 1,5%ige CO2-Luft-Begasung) vonChlorella pyrenoidosa, Stamm Emerson (Algensammlung Pringsheim 211–8 b) wird die zellteilungsfreie Zeit von etwa 20 Std Dauer in drei Entwicklungsabschnitte gegliedert.2.Einem 1. Entwicklungsabschnitt folgt die Induktion der Zellteilungen (2. Entwicklungsabschnitt). Im 3. Abschnitt findet weiteres Wachstum statt, ohne daß sich die Zahl der später zu beobachtenden Autosporen erhöht.3.Durch vergleichende analytische Bestimmungen von Protein, Kohlenhydraten und Nucleinsäuren wird versucht, biochemische Koinzidenzen mit den genannten Entwicklungsabschnitten zu finden.4.Während die Bildung von Protein schon im ersten Entwicklungsabschnitt der Zellentwicklung sehr ausgeprägt ist, findet die Hauptvermehrung vermehrung der Kohlenhydrate im 2. und 3. Abschnitt statt. Die RNS-Bildung zeigt keine Beziehung zu den beschriebenen Entwicklungsabschnitten, dagegen ist die DNS-Vermehrung weitgehend auf den 2. Abschnitt (Teilungsinduktion) beschränkt.Unter den gegebenen Versuchsbedingungen ist die Proteinsynthese im Entwicklungsverlauf der Zellen nur anfänglich von einer RNS-Vermehrung begleitet.5.Die erhaltenen Ergebnisse werden mit den Befunden anderer Autoren verglichen.

Changes in the Enzyme Pattern in Synchronous Chlorella sorokiniana caused by Different Nitrogen Sources

Summary Changes in enzyme pattern in synchronous Chlorella sorokiniana (high temperature strain) due to changes in nitrogen source have been investigated. Regulation of nitrogen metabolism caused by change in the nitrogen source mainly effects the nitrate reducing system, glutamine synthetase, glutamate synthase and NADP-glutamate dehydrogenase. An intermediary effect has been shown on NAD-glutamate dehydrogenase and glutamate-oxalacetat-transaminase which were not directly involved in the regulating process.

Correlation Between Pigment Systems and Photosynthetic Activity During the Developmental Cycle of Chlorella

Summary Concentration of pigments, spectral changes within the photosystems and their activities during the developmental cycle of synchronous Chlorella were investigated. The ratio of PSI/PSII activity is inversely related to the ratio of the corresponding low temperature emission signals from these systems. This is interpreted as occuring of only partly active chlorophyll at certain stages of the cycle. Extreme values for the parameters were found at the 6th and 12th hour. They are discussed in relation to other phenomena outside the chloroplast during the developmental cycle.

Synchronous cell divisions in Anacystis nidulans Richter

SummaryThe blue-green alga, Anacystis nidulans was successfully synchronized in continuous light (15,000 lux) by a 14 hr cycle, consisting of 8 hrs at 26°C, and 6 hrs at 32°C, coupled with periodic dilution of the algal suspension to a constant cell number at the end of each cycle. The alga continues to grow at the lower temperature, and a “division burst” begins 2 hrs after transfer to the higher temperature.ZusammenfassungDie Cyanophycee Anacystis nidulans wurde in Dauerlicht von 15 000 Lux vollständig synchronisiert. Die Cyclen bestehen aus 8 Std bei 26° C und 6 Std bei 32° C, an ihrem Ende wurde jeweils mit frischer Nährlösung auf die Ausgangszellzahl von 3·107 Zellen/ml verdünnt. Bei beiden Temperaturen kann sich die Alge vermehren, unter den synchronisierenden Bedingungen des Temperaturwechsels beginnt der Teilungsschub (Verdopplung der Zellzahl) bei 32° C nach 2 Std.

Molecular hydrogen: A new inhibitor of photosynthesis in the blue-green alga (cyanobacterium), Anabaena sp. TA 1

Molecular hydrogen strongly inhibits C2H2-reducing activity in intact cells of Anabaena sp. TA 1 in the light under anaerobic conditions. The inhibitory effect can be partially relieved by supplying the cells with molecular oxygen. When cells of Anabaena sp. TA 1 were grown under anaerobic N2-fixation conditions in the presence of 0.05 bar H2 with white light a pronounced decrease of growth rate occurred. With ammonium ions as nitrogen source the inhibitory effect of H2 was less pronounced.Concomitant with the reduced growth under N2 in the presence of H2 a loss of blue-green pigmentation was observed due to a diminished phycocyanin content. On the other hand, the concentration of carotenoids and chlorophyll remained nearly constant. With NH4+as nitrogen source nearly no alteration of phycocyanin content occurred upon incubation with H2.In addition, H2 induced a random distribution of thylakoid membranes in vegetative cells which normally exhibited a curved, parallel pattern. In heterocysts, however, photosynthetic membranes were always arranged randomly.Under far red light, growth and activity of photosystem II were largely diminshed. Under these conditions H2 exhibits an additional inhibitory effect. However, compared to 62% growth inhibition under white light, a decrease of only 20% occurred.Measurements of the photosynthetic electron flow with isolated thylakoid membranes showed that oxidation of diphenylcarbazide (DCP) by membranes from H2-grown cells was inhibited by 28% compared to membranes from control cells. Using ascorbate/DCPIP as electron donor an inhibition of only 1–4% was measured. It is concluded, that H2 inhibits electron flow in the photosynthetic electron transport chain at a site between photosystem II and photosystem I.

Changes in the Activity of Enzymes Involved in Nitrogen Metabolism in Maize Seedlings Dependent on Different Nitrogen Sources

Summary 1. Changes in the specific activities of nitrate reductase, glutamine synthetase and NAD + NADP glutamate dehydrogenase were estimated in seedlings of Zea mays for 20 d after germination. 2. N-starvation resulted in a lengthening of the roots, while the increase in shoot lenght was reduced. 3. The activities of the enzymes observed were higher in the roots than in the shoots. Probably a major role of the root in N-metaboism can be interpreted from this observation. 4. Recovery from N-starvation first increased the activities of enzymes investigated in the roots. With different delays their activities increased also in the shoots. The capacity to abolish N-starvation is only slightly reduced in both roots and shoots during starvation. 5. The nitrate reductase activity in the roots was limited by the NO3- supply. If the NO3- supply was enhanced, nitrate reductase activity increased via de novo synthesis.

Chapter 10 Hmdling and Culturing of Chlorella

Publisher Summary This chapter discusses successful culturing and growing of Chlorella and other unicellular green algae. The organisms comprising the genus Chlorella are nonmotile, globular, unicellular green algae with an average diameter of 4 to 10 μ . Chlorella are dependent on light for autotrophic growth; therefore, the course of the growth curve is governed by the illumination of the culture. For most investigations three species of Chlorella are in use. These are C. vulgaris , C. pyrenoidosa , and C. ellipsoidea . In all of these species different strains are known, which differ markedly in physiological characteristics. Pure cultures are always derived from a single parent cell and are propagated with the precautions necessary to prevent contamination by other microorganisms. Moreover, to retain these cultures over a longer period of time, it is advantageous to prepare test tube cultures using media solidified with 1% agar. In connection with the handling and keeping of stock cultures over a period of years, the problem of constancy with respect to morphological and physiological characteristics is very important. Among most of the frequently used strains of Chlorella there is no evidence of a tendency for much spontaneous mutation. To obtain synchronization in cultures of Chlorella, a change of at least one external factor is required. Although autotrophic microorganisms can generally be grown in continuous light, the light-dark change seems to be the most suitable procedure to synchronize Chlorella.

Changes in pigment content, lipid pattern and ultrastructure of synchronous Chlorella after heat and cold shocks

Completely synchronous Chlorella cultures were treated with heat (45°C) or cold shocks (4° C) of different lengths at the sixth hour of the 14:10 h lightdark-cycle. After the treatment the cells were grown under normal conditions. Analysis at the end of the cycle showed a direct connection between pigment bleaching, reduction of lipid content, loss of thylakoid stacking and a shift of the fluorescence emission maximuminto a region of shorter wavelength. The thylakoid stacking was completely loosened after a heat shock while two thylakoids remained in contact after cold treatment. This probably explains the different regeneration capacities in temperature shock treated cells. None of the described effects could be observed directly after the shocks. From the parallel decay of chlorophyll a, monogalactosyl diglyceride and carotenoids an intimate correlation with the photosystem II complex is suggested.

Activation of the Nitrate Reducing System in Synchronous Chlorella 211-8k (high temperature strain)

Summary The conditions of light mediated activation of nitrate reductase (EC 1.6.6.1.) and nitrite reductase (EC 1.6.6.4.) were investigated. The close connection of nitrite reductase (NIR)1 activation to the photosynthetic apparatus was emphasized by the action of jodacetamide, CCCP and light intensity. Replacing the Mo in the normal nutrient with W results in an inactive NAR. But the light mediated activation of NAR occurs too. That was demonstrated by suspending that algae in Mo nutrient in the presence of actidion. There is some evidence that the activation of W-NAR by addition of Mo bases on an exchange of W with Mo directly in the enzyme.