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Studies on photosynthesis: some effects of light of high intensity on Chlorella

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Abstract

1. The effect on oxygen evolution of Chlorella vulgaris produced by light intensities up to about 40,000 f.-c. has been studied by the use of the Warburg technique. 2. Above a certain critical intensity, which is determined by the previous history of the cells, the rate of oxygen evolution decreases from the maximum to another constant rate. This depression is at first a completely reversible effect. 3. With a sufficiently high intensity this constant rate represents an oxygen uptake greater than the rate of dark respiration. During such a constant rate of oxygen uptake a progressive injury to the photosynthetic mechanism takes place. After a given oxygen consumption the rate falls off, approaching zero, and the cells are irreversibly injured. 4. The constant rate of oxygen evolution (2 and 3) decreases in a continuous manner with increasing light intensities, approaching a value which is approximately constant for all lots of cells regardless of previous history. 5. Two alternative hypotheses have been presented to explain the observed phenomena. The more acceptable of these proposes quick inactivation of the photosynthetic mechanism, the extent of inhibition depending on the light intensity. 6. In Chlorella vulgaris solarization is influenced by the previous history of the cells.

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... Photoinhibition induced by a higher PFD has been documented in field studies (62), and earlier studies have been reviewed (92,138). With algae grown at low PFD, sudden exposure to PFDs ranging from only 50 /Lmol m-2s-1 (160) up to full sunlight resulted in photoinhibition of the light saturated (14, 57,68,94,139,141,145,160) saturated photosynthetic capacity and the photon yield and showed that photo inhibition commenced within minutes of transfer of shade clones from a low to a high PFD (54; however, see also 101). Similarly, a fern from the rainforest floor was shown to suffer photoinhibition within minutes of transfer to full sunlight conditions (112). ...
... Plants acclimated to growth at low PFDs and exposed to a high PFD are more severely photoinhibited than plants acclimated at a higher PFD (94,109,112,145). This difference highlights the importance of photosynthetic capacity in influencing the extent of susceptibility to photoinhibition. ...
... When intact leaves or photosynthetic organelles were exposed to a moderate PFD without carbon metabolism, photoinhibition could be totally alleviated by maintenance of a certain minimal rate of photosynthetic carbon metabolism throughout the light exposure (24, 31-33, 46,69,75,106,111). Similarly, the photoinhibi tion evident when low-PFD-adapted plants are exposed to high PFD is less if carbon metabolism occurs throughout the period of light exposure (13, 14, 94,105,109,112,160). While the maintenance of photosynthesis throughout exposure to moderate to high PFDs is necessary for avoidance of photoinhibi tion, the explanation for this protection remains obscure. ...
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... And it has not changed in the sixty years since.' This experiment was published by Myers and Burr (1940) -the discovery of quenching of photosynthesis by high light, the phenomenon of photoinhibition, but without its name. Only in 1956, did Kok characterize this phenomenon in an elegant manner (Kok 1956). ...
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... Photoinhibition has received intermittent attention for almost a century (33, 64,66,67,91,129), but wider recognition and interest has only developed in the last two decades. Powles (112) and Neale (92) reviewed the many, largely observational studies of photoinhibition on terrestrial plants through 1984 and aquatic plants through 1987, respectively. ...
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Chlorophyll bleaching induced by suboptimal temperatures in Chlorella sorokiniana was shown by Marvin and Karlander(5) to require light and molecular oxygen. The present study with various light qualities and quantities showed that bleaching was light intensity dependent and a two-phase process. White fluorescent light was the most efficient in degrading chlorophyll, then in order, blue, incandescent white, and red. Low intensity blue, 2.55–4.0 mW/cm2, and red light, 2.8 mW/cm2, produced an initial decline in chlorophyll more rapid than higher intensities of blue or red light. The low intensity blue and red light curve also showed a mid time-course plateau lasting beyond 100 hr. No mid time-course plateau occurred at low intensities of fluorescent or incandescent white light.Oxygen evolution declined with increasing time of incubation at 10°C. Blue light of 4.0 mW/cm2 was least destructive, extending the duration of oxygen evolution to nearly 4 times that obtained with white light. Cells incubated at temperatures greater than 22°C exhibited patterns of photosynthesis and respiration approaching those of control cells at 39°C. Cells incubated at temperatures less than 22°C showed patterns approaching those of cells subjected to bleaching at 10°C.Hill activity was destroyed during the initial lag phase before much loss of chlorophyll had occurred. Viability of cells was more closely associated with loss of chlorophyll in the accelerated bleaching phase.
Article
At the beginning of our century few scientists paid attention to the phenomenon of inactivation of photosynthesis by high light intensities which was later called photoinhibition. In the period 1925-1950, the idea was established that photoinhibition is a reversible inactivation, determined by light intensity and exposure time, followed by irreversible damage of the photosynthetic apparatus. However, the absence of a uniform terminology demonstrates that photoinhibition was not completely perceived and understood. In 1956, B. Kok gave the first definition of photoinhibition as a photochemical inactivation of pigment complexes.
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This account is focused upon the early part of my career in order to illuminate the logistics and the culture of our science in the period 1936 to 1949. A roundabout path took me from a farm in Pennsylvania to a PhD under George Burr at Minnesota in 1939. In studying the photosynthetic competence of chlorophyll formed by the green alga Chlorella in darkness, I stumbled upon the phenomenon of photoinhibition. In a two-year postdoctorate at the Smithsonian Institution, I worked under E.D. McAlister. Our major accomplishment was in making simultaneous recordings of fluorescence and CO2 uptake during the induction period. Variations in photosynthetic behavior of Chlorella led to a study of culture conditions and a recognition of the changing conditions which occur in batch cultures. A continuous culture apparatus (turbidostat) was developed as a means of attaining steady-state growth and production of uniform experimental material. I exploited the device in work at my first (and only) position at The University of Texas in 1941 and subsequent years. Study of the CO2/O2 gas exchange ratio led to the recognition of the important role of nitrate in the photosynthetic metabolism of algae. The account ends with the 1949 American Association for the Advancement of Science symposium.
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Experiments on the grazing of the ciliate Colpoda steinii on the blue–green alga Anacystis nidulans showed, among other things, that declines of the algal population initiated by grazing often continued for several days after grazing pressure had been released. In addition, long lags were observed when this alga was inoculated into sterile culture medium. Evidence presented in this study indicates that both phenomena were due to cellular damage caused by exposure of algal cells to a sudden increase of light intensity (“light shock”). The occurrence of light shock appeared to exert a destabilizing influence on the grazing relation between Colpoda and Anacystis.
Article
The effect of photoinhibition on the activity of photosystem II (PSII) in spinach chloroplasts was investigated. Direct light-induced absorbance change measurements at 320 nm (ΔA320) provided a measure of the PSII charge separation reaction and revealed that photoinhibition prevented the stable photoreduction of the primary quinone acceptor QA. Sensitivity to photoinhibition was substantially enhanced by treatment of thylakoids with NH2OH which extracts manganese from the H2O-splitting enzyme and prevents electron donation to the reaction centre. Incubation with 3-(3,4,-dichlorophenyl)-1,1-dimethylurea (DCMU) during light exposure did not affect the extent of photoinhibitory damage. The chlorophyll (Chl) b-less chlorina (2 mutant of barley displayed a significantly smaller light-harvesting antenna size of PSII (about 20% of that in wild type chloroplasts) and, simultaneously, a lower sensitivity to photoinhibition. These observations suggest that photoinhibition depends on the amount of light absorbed by PSII and that the process of photoinhibition is accelerated when electron donation to the reaction centre is prevented. It is postulated that the probability of photoinhibition is greater when excitation energy is trapped by P680+, the oxidized form of the PSII reaction centre. The results are discussed in terms of the D1/D2 heterodimer which contains the functional PSII components P680, pheophytin, QA and QB.
Article
During the last decade it has been recognized that the process of photosynthesis in green plants is unique, not because it involves a complicated photochemical decomposition of carbon dioxide for which there is no analogy in the organic world, but because it combines in a unique manner a number of processes each of which may be found in other living cells. If we turn from green plants to purple bacteria, for instance, we find that radiant energy is utilized for the reduction of carbon dioxide. These organisms, however, cannot use simply water as a hydrogen donor and hence are not able to liberate free oxygen. For the reduction of carbon dioxide they depend, in addition to light, upon energetically valuable hydrogen donors such as free hydrogen, hydrogen sulphide, or organic acids. The over-all energy balances of these photoreductions are, therefore, much less favourable than that of photosynthesis in plants. If we turn to organisms not sensitive to light, we find that carbon dioxide can be reduced in complete darkness by several species of bacteria and even by some animal tissues. In this case the mechanism is a coupled oxido-reduction in which an excess of hydrogen donors, either of inorganic or organic nature, has to be sacrificed to promote the ‘chemosynthesis’. It is clear that such dark reactions lead not to a gain but to an over-all loss of chemical energy.Recent advances in the field of respiration and fermentation have taught us that despite the infinite variety of metabolic reactions in living cells the principles governing them are few. Accordingly, it is conceivable that the different reactions involving a reduction of carbon dioxide have many important traits in common, and that the study of any one of them may lead to a better understanding of the process of photosynthesis.The present article is a report on the metabolism of certain unicellular chlorophyllous algae (several species of Scenedesmus, Ankistrodesmus, Rhaphidium) that are able to reduce carbon dioxide either in normal photosynthesis with the evolution of oxygen, or in photo-reduction with the absorption of an equivalent amount of hydrogen, or in chemosynthesis with the oxyhydrogen reaction as the driving force. The two latter reactions do not occur under normal aerobic conditions. They can be observed only after a few hours' incubation in hydrogen gas. The anaerobic treatment brings into play a hydrogenase which enables the algae to absorb or to release molecular hydrogen. This metabolic change we call adaptation. The adaptation consists in an enzymatic activation or rearrangement of some of the catalytic systems. It can be inhibited by traces of specific poisons like cyanide and hydroxylamine.Upon illumination in the adapted state, in presence of hydrogen and carbon dioxide, the algae reduce carbon dioxide with twice the volume of hydrogen, exactly akin to some purple bacteria. This we call photoreduction. The results of experiments with flashing light and with specific poisons show that in photosynthesis and photo-reduction the truly photochemical reactions are the same and remain unchanged. Hence, the difference appears to originate from the ways by which the oxidized products of the photochemical reaction are eliminated. In photosynthesis they are decomposed with the liberation of oxygen, in photoreduction they are reduced to water by hydrogen donors.The adapted state of the algae gives way to normal aerobic conditions not only under the influence of air, but also under the influence of higher light intensities. This we call reversion. It seems that reversion occurs whenever some intermediate oxidized products (which we call ‘peroxides’, because they must be the precursors to molecular oxygen) accumulate faster than they are reduced by the hydrogenase system. In absence of carbon dioxide no intermediate oxidized products (or ‘peroxides’) are formed and the adapted state is stable even at high light intensities. If not only carbon dioxide but also hydrogen is absent (i.e. in an atmosphere of pure nitrogen), light causes a release of hydrogen from the adapted algae. The reversion by light in presence of carbon dioxide can be prevented by the action of certain substances like hydroxylamine, or o-phenanthroline, In the presence of such inhibitors the adapted algae continue to metabolize like purple bacteria even in very strong light. The light saturation rate of carbon dioxide reduction with hydrogen remains, however, far smaller than the corresponding rate of photosynthesis.Very small amounts of oxygen prevent adaptation, but up to 10mm. Hg of this gas are tolerated by adapted algae in hydrogen. The reason is that at these low partial pressures the reduction of oxygen to water in the algae proceeds faster than the reversion. Under optimum conditions the formation of water from the elements, the oxyhydrogen reaction, is coupled with a simultaneous reduction of carbon dioxide, so that one-half molecule of carbon dioxide disappears for each molecule of reduced oxygen. 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I am particularly indebted to Dr E. Rabinowitch for a very thorough criticism of the manuscript.
Article
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Chapter
Quantum EfficiencySaturation PhenomenaInduction PeriodsPhoto-Oxidation Processes in PlantsThe Metabolism of the Purple Bacteria and van Niel's Theory of PhotosynthesisCarbon Dioxide Reduction in the Absence of Oxygen and the “Reduced State” of the Assimilating System in PlantsThe Reduction of Carbon Dioxide in the Dark
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Article
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Article
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Chapter
The ability to derive basin-scale maps of phytoplankton chlorophyll in the upper ocean from satellite color sensors (see Lewis, this volume) has led increasingly to the development of models relating biomass to primary production (Eppley et al., 1985; Falkowski, 1981; Platt, 1986; Platt and Sathyendranath, 1988; Morel, 1991). Chlorophyll, however, represents a pool size, while primary production is a flux. To derive a flux from a pool, a time-dependent variable must be incorporated. The simplest models relating carbon fixation to chlorophyll incorporate irradiance (Bidigare et al., this volume); the transfer function is a quantum yield. These so-called light-chlorophyll models (Ryther and Yentsch, 1957; Cullen, 1990) are virtually impossible to verify in the ocean, hence their credulity presumably lies in understanding the underlying biological processes and how those processes are regulated. Here, I examine how some of the key parameters which are implicitly or explicitly incorporated in rational light-chlorophyll models are regulated at a fundamental, molecular level.
Article
Historians and philosophers of twentieth-century life sciences have demonstrated that the choice of experimental organism can profoundly influence research fields, in ways that sometimes undermined the scientists’ original intentions. The present paper aims to enrich and broaden the scope of this literature by analysing the career of unicellular green algae of the genus Chlorella. They were introduced for the study of photosynthesis in 1919 by the German cell physiologist Otto H. Warburg, and they became the favourite research objects in this field up to the 1960s. The paper argues that dealing with Chlorella’s high metabolic flexibility was crucial for the emergence of a new conception of photosynthesis, as a plastic, integrated system of pathways. At the same time, it led to new collaborations between physiologists and phycologists, both of whom started to re-orient their studies in ecologically informed directions. Following Chlorella’s trail, hence, not only elucidates how experimental organisms forced scientists to change their conceptual approaches and techniques, but also provides insight into the interaction of different lines of research of mid-twentieth century plant sciences.
Article
Microalgal strains of the genus Scenedesmus are a promising resource for commercial biotechnological applications. The temperature-, pH- and light-dependent growth of Scenedesmus ovalternus has been investigated on a laboratory scale. Best batch process performance was obtained at 30 °C, pH 8.0 and an incident photon flux density of 1300 μmol photons m² s¹ using a flat-plate gas-lift photobioreactor. Highest growth rate (0.11 h¹) and space-time yield (1.7 ± 0.1 gCDW L¹ d¹) were observed when applying these reaction conditions. Biomass concentrations of up to 7.5 ± 0.1 gCDW L¹ were achieved within six days (25.0 ± 0.5 gCDW m² d¹). The light-dependent growth kinetics of S. ovalternus was identified using Schuster’s light transfer model and Andrews’ light inhibition model (KS = 545 μmol photons m² s¹; KI = 2744 μmol photons m² s¹; μmax = 0.21 h⁻¹). The optimal mean integral photon flux density for growth of S. ovalternus was estimated to be 1223 μmol photons m² s¹.
Chapter
Für die assimilatorische Tätigkeit sind die aktuellen Außenfaktoren und die aktuellen inneren Faktoren der Pflanze ausschlaggebend. Da die Innenfaktoren aber nicht stabil sind, sondern ihrerseits mit den Veränderungen der Umweltfaktoren schwanken können, hängt die assimilatorische Tätigkeit vom Vorleben der Pflanze ab. Durch Nachwirkungen der Außenfaktoren kann die Assimilations-intensität gesteigert oder abgeschwächt werden. Wenn diese Nachwirkungen zu einer Steigerung der photosynthetischen Tätigkeit führen, spricht man von „Induktion“, „Aktivierung“ (Stimmungsänderung, Einstellung) usw.; wenn die Wirkung in einer Abschwächung besteht, wird sie mit Ausdrücken wie „Inaktivierung“, „Hemmung“, „Ermüdung“ usw. bezeichnet.
Chapter
Die Frage des Einflusses der während der Vorgeschichte des Versuchsmaterials vorhandenen Umweltbedingungen auf die später gemessene Photosynthese ist wiederholt in vielen Arbeiten — in der älteren Literatur besonders unter dem Gesichtspunkt der modifikativen Anpassung — untersucht worden. Hier zeigte sich bisher, daß zahlreiche Faktoren bei verschiedener Anzucht und bei unterschiedlichen Kulturbedingungen die spätere Photosynthese verändern können. Unter diesen Faktoren beansprucht sowohl die während des „Vorlebens“ vorhandene Gasatmosphäre (aerob, anaerob, CO2-Gehalt, Wasserstoffgehalt der Atmosphäre) als auch der zu Modifikationen führende Wassergehalt im Boden und dessen Salzgehalt bei höheren Pflanzen eine gründliche Berücksichtigung. Weiterhin ist der Einfluß der verwendeten Nährlösung (Zusammensetzung, Konzentration, pH-Wert, Dauer ihrer Einwirkung etc.) oft entscheidend für die spätere photosynthetische Leistung. In engem Zusammenhang hiermit steht das jeweils während der Vorgeschichte erreichte Alter (Kulturdauer und auch physiologisches Alter) der Versuchspflanzen. Auch der Einfluß der in der Vorgeschichte aufgeprägten Rhythmik darf nicht außer acht bleiben. Schließlich sind die Temperatur-bedingungen, die Beleuchtungsstärke und der Spektralbereich des Anzuchtlichtes während des Vorlebens für die spätere Höhe der CO2-Assimilation von Bedeutung.
Chapter
Nach kürzerer oder längerer Belichtung von Blättern der Landpflanzen, aber auch von submersen Pflanzen, ist öfters eine Herabsetzung der Photosynthese beobachtet worden. Als Ursachen dieser Depression werden erwähnt: Spalten-Schluß, Temperaturinaktivierung, Photoinaktivierung (Solarisation), Verlagerung der Chloroplasten, Steigerung der Atmung im Licht und Anhäufung von Assimilaten. Nur die letztere Möglichkeit soll näher betrachtet werden. Der Begriff Assimilate (oder biochemisch präziser Photosynthate) wird hier ohne scharfe Abgrenzung verwendet. Als Photosynthate werden sowohl die Primärprodukte als auch Zucker und Stärke zusammengefaßt. Nach Smith (1944) wird, jedenfalls in Blättern von Helianihus annuus, eine der CO2-Aufnahme äquivalente Menge von Kohlenhydraten akkumuliert; der Gehalt an Stärke und Saccharose + Monosaccharide steigt proportional mit der absorbierten CO2-Menge.
Chapter
Der Einfluß der Beleuchtungsstärke auf die Geschwindigkeit der Photosynthese ist eines der großen Probleme, für die sich die Pioniere der Photosyntheseforschung schon frühzeitig interessierten (Ingen-Housz 1779, Senebier 1782). Späterhin hat man sich immer wieder damit beschäftigt, und nun gehört es schon lange zu den Photosyntheseproblemen, die am häufigsten Gegenstand von Untersuchungen gewesen sind. Was die länger zurückhegende Forschungsarbeit betrifft, muß in dieser Übersicht auf Pfeffers Handbuch der Pflanzenphysiologie (Band 1, Stoffwechsel, 1897) verwiesen werden; außerdem können die drei vorliegenden größeren Photosynthesemonographien (Stiles’ 1925, Spoehrs 1926 und Rabinowitchs dreibändiges Werk 1945, 1951, 1956) die Darstellung in vielen Punkten ergänzen.
Chapter
In respiration all plants exchange gases with the surrounding medium, and with the exception of a few microorganisms this exchange consists of an absorption of oxygen by the plant from the medium and an evolution of carbon dioxide from the plant into the medium. With most vascular plants the medium is a double one, air and soil, exceptions being found in a few completely aerial plants and in water plants which may or may not be rooted in soil and which may be completely or only partially submerged. With most of the Bryophyta the bulk of the gaseous exchange takes place between the plant and air, the rhizoids attaching the plants to the soil forming only a very small portion of the plant. Apart from a comparatively small number of terrestrial forms the algae live in an aqueous medium which may be a weaker or stronger solution, mainly of inorganic salts, according to whether the plants live in fresh or salt water. The media with which gaseous exchange takes place are thus air, soil, fresh water and salt water, according to the species.
Chapter
The response of photosynthetic organisms to high or excessive photon flux densities (PPFD) is a topic which interested several investigators in photosynthesis research during the first half of the twentieth century (e.g. Emerson 1936; Myers and Burr 1940; Kok 1956). Until recently, the phenomenon of photoinhibition, the inhibition of photosynthesis by excessive light, was equated with damage to the photosynthetic apparatus (Powles 1984; see also Demmig-Adams and Adams 1992a). In the majority of studies on photoinhibition, it is, in fact, likely that some form of damage was responsible for the majority of the decrease in photosynthetic competence observed, as most studies have involved the exposure of leaves, organisms, or even isolated chloroplasts or thylakoids to PPFD which was many times greater than that experienced during development.
Chapter
In dem vorliegenden Abschnitt sollen die Grundlagen der Wirkungen von Licht und Strahlung auf biologische Objekte, besonders auf die einzelne Zelle, dargestellt werden. Hierüber gibt es eine höchst ausgedehnte Literatur, die insgesamt zu behandeln völlig unmöglich ist. Abgesehen von den später erwähnten Originalarbeiten und Zusammenfassungen einzelner Gebiete sei auf die folgenden, grundlegenden Werke hingewiesen: Dessauer [2], Hollaender [2, 3], Lea, Nickson, Rabinowitch [1, 2], Rajewsky, Timoféeff-Ressovsky und Zimmer, Sommermeyer. Allgemeine Zusammenfassungen finden sich besonders in Butler und Randall (Progress in Biophysics and Biophysical Chemistry), sowie in den Fortschritten der Botanik (Simonis).
Article
Photosynthesis, the mechanism responsible for O2 evolution on Earth, is also a critical instrument for fuel of the future. Observations on algal biotechnology, and tracing back algae utilization to ancient tribes, give key clues to the development of new-generation biofuels. Microalgae as a promising photosynthetic "farm" have numerous aspects from foods to medicines to biofuels. The starting point of algal biofuels also comes from the awareness of the requirement for a better source. Conventional fossil fuels are argued to be depleting and alternative biofuels are discussed to be competitive and promising in real case leaving possible scenarios. With this knowledge, tracing the historical development of microalgal biofuels in the scope of photosynthesis, production technologies, possible biofuel types, and genetic engineering tools as a relatively new concept have been discussed and highlighted in this chapter. Also the global projects and their contribution to the literature are pointed out to observe logical results for the development of microalgal biofuels.
Chapter
Petroleum based fuels are accepted as unsustainable because of depleting supplies and cause of accumulation of CO2 in the environment. Out of the other sources of energy, which are generally considered to be alternative source of energy, algae based biofuel is comparatively new idea. The oil content of various microalgae is up to 80% of their dry biomass. Photosynthesis based biofuel production summarize energy production with biological carbon dioxide fixation. Ideally they are carbon neutral, and they minimize emission of greenhouse gases. Microalgae are the group of microorganisms, which contains a huge amount of triacylglycerol inside the cellular organization, which produces FAME (fatty acid methyl esters) via trans-esterification process. They also require a least land area relative to other biofuel crops. They are highly promising biofuel source. The production of biofuel from microalgae is a complex process. It comprises microalgae cultivation in a low cost nutrient medium, harvesting of cells from cultivation medium. Heavy investment in microalgae cultivation, harvesting and processing require very high productivities, greatly exceeding those of terrestrial crops. The maximum achievable photosynthetic efficiency, and thus biomass productivity, of microalgae cultures has been controversial for nearly a century and is still unresolved, as reflected in recent peer reviewed literature. Actual and projected microalgae biomass productivities, based on commercial production, outdoor experimental work, laboratory data and theoretical projections, range from about 20 to over 200 mt dry organic matter/hectare-year. Methods of genetic modifications of algal strains to be more efficient in the production of biofuels are still in their infancy. One of the main goals of genetic engineering in this relation is to improve algal strains so that they can create a source of alternative energy that is more environmentally friendly and sustainable for the accumulation of lipid content in their cells which can be utilized as source of biodiesel.
Article
1. Crude suspensions of chloroplasts show a distinct accessory respiration in the dark. 2. During illumination of such suspensions evolution of oxygen is not observed, on the contrary the uptake of oxygen increases 2-3 fold. 3. The accessory respiration of crude suspensions of chloroplasts in the dark is not inhibited by HCN (up to 0.04%). The uptake of oxygen during the illumination period is increased by a moderate HCN concentration (0.02%) and retarded somewhat by higher concentrations (> 0.04%). 4. The uptake of oxygen is not affected by the addition of glucose either during the dark period or during illumination. 5. The uptake of oxygen is increased by the addition of asparagine both in the dark and during illumination. The increase in uptake of oxygen on addition of asparagine during the period of illumination may exceed considerably the increase which occurs on addition of asparagine during the dark period. 6. The addition of manganese does not affect the rate of uptake of oxygen during the dark period, when added during the illumination period the uptake of oxygen is often temporarily markedly increased. 7. Chlorosis brought about by a too high manganese iron ratio is assumed to be caused by photo oxidation of chlorophyll which is a secondary effect of the rapid destruction of the protective protein substances in the presence of extremely high redox potentials.
Chapter
Bereits im vorigen Jahrhundert erkannten Boussingault (1865) und Pringsheim (1887), daß manche Pflanzen unter anaeroben Bedingungen die Fähigkeit zur Photosynthese verlieren. Die sich daraus ergebende Frage nach einer Notwendigkeit von Sauerstoff für die Photosynthese ist seither oft experimentell bearbeitet und diskutiert worden, ohne daß jedoch bisher eine allgemein akzeptierte Klärung des Problems erreicht worden wäre. Manche der in der Literatur vorhandenen Widersprüche dürften jedoch einfach auf der Verwendung verschiedener Versuchsobjekte mit unterschiedlicher Empfindlichkeit gegen Anaerobiose beruhen. Auch spielt das methodische Problem der Beseitigung der letzten O2-Spuren eine wesentliche Rolle. Schließlich ist streng zu unterscheiden zwischen einer etwaigen sofortigen Wirkung von O2-Entzug auf die Photosynthese und den durch langdauernde anaerobe Vorbehandlung im Dunkeln hervorgerufenen Erscheinungen. In letzterem Fall ist meist mit Sekundäreffekten, bedingt durch Anhäufung von Gärprodukten, zu rechnen. Es besteht demgemäß die Möglichkeit einer direkten oder einer indirekten Wirkung der Anaerobiose. Aus diesen Gründen kommt solchen Befunden, in denen sich eine Unempfindlichkeit der Photosynthese gegen O2-Entzug ergibt, eine größere Bedeutung zu als der Beschreibung von Photosynthesehemmungen bei unter Umständen besonders anaerobioseempfindlichen Organismen. Im Prinzip ist sogar zu postulieren, daß der zweifelsfreie Nachweis einer ungehemmten Photosynthese bei vollständigem O2-Ausschluß an einem einzigen Objekt genügen sollte, alle Theorien, die eine Notwendigkeit von molekularem Sauerstoff oder aerober Atmung für die Photosynthese fordern, ad absurdum zu führen.
Chapter
Photoacclimation is a suite of phenotypically expressed, developmentally independent, reversible physiological feedback responses to short-term (minutes to days) variations in spectral irradiance. These responses are observed in all eukaryotic algal taxa and involve alterations in the optical absorption cross section, the effective absorption cross section, and the rate of electron transfer from water to a terminal acceptor (e.g., carbon dioxide or nitrate). In this chapter, we review the primary physical processes in aquatic ecosystems that provided selection pressure for photoacclimation responses. These processes include the passage of clouds across the sky, vertical mixing, and diel variability in incident solar irradiance. The physiological responses to variations in the spectral irradiance are transduced via the redox state of intersystem electron transport components, especially plastoquinone. In a ‘nested’ series, responses include state transitions, alterations in the xanthophylls, and net synthesis/degradation of light harvesting complexes. The three processes have different time constants and dynamic ranges, but all result in alterations of the effective absorption cross section of photochemistry, such that light absorption and electron transport are balanced. The balance between light absorption and electron transport optimizes (not maximizes) photosynthesis under a very wide range of light conditions found in natural aquatic ecosystems.
Article
The possible protection against photo-oxidative degradation of chlorophyll and carotene in Cucumis leaf discs at 1°C by a wide variety of compounds was investigated. Dimethyl sulphoxide and glycerol as well as ferricyanide, ascorbate, KCN and hydroxylamine were ineffective. Photo-oxidation was, however, at least partly, prevented by benzoquinone, hydroquinone, naphtoquinone, guajacol, benzidine, diaminobenzidine, alizarinesulphonicacid, triphenyltetrazoliumchloride and 3-(3,4-dichlorophenyl), 1,1-dimethylureea. Photo-oxidative damage was promoted by salicylaldoxine, disalicylidenediaminopropane, azide, ethylenediamine tetraacetic acid, trishydroxymethylaminomethane, diquat and benzylviologen. It was also increased at high pH values. It is suggested that the mechanism of protection of Cucumis leaf chloroplasts against low temperature photo-oxidative damage is a protection of the electron transport pathway from the reducing to the oxidizing side of the photosystems.
Article
La plupart des végétaux chlorophylliens présentent, à la lumière, un dégagement de CO2 et une absorption d'O2 plus importants qu'à l'obscurité. Ces mouvements sont dûs, pour une grande part, au métabolisme de l'acide glycolique, engendré par la fonction oxygénasique de la RuBP carboxylase. L'absorption d'oxygène s'effectue, à la fois, dans les chloroplastes, les peroxysomes et les mitochondries. L'émission de gaz carbonique est surtout mitochondriale. Elle peut être évaluée, chez un végétal de type C3, à environ 4 à 5 fois la respiration obscure et à au moins 30% de la photosynthèse nette. Bien qu'on n'ait pu attribuer une fonction précise à la photorespiration considérée comme une conséquence inévitable de la teneur en oxygène de l'atmosphère, les tentatives d'inhibition de ce processus se sont révélées néfastes pour les végétaux. Les plantes de type C4 pallient les inconvénients de la photorespiration par une organisation efficace.
Article
Increasing energy demands, predicted fossil fuels shortage in the near future, and environmental concerns such as the production of greenhouse gas carbon dioxide have motivated the search for alternative and cleaner energy sources. Biodiesel has received much attention in recent years and production of biodiesel from microalgae is a newly emerging field. Microalgae possess a high growth rate, utilize solar light, water and CO2 to convert these to sugars, from which macromolecules, such as lipids and triacylglycerols (TAGs) can be obtained making microalgae more photosynthetically efficient than oil crops. Microalgae are represented as a potential source of biomass, having great biodiversity and variability in their biochemical composition. This paper presents an overview on microalgae with particular emphasis as a source for biofuel and its other applications. Future research and development aspects regarding microalgae and microalgal fuel production are also discussed.
Article
Zusammenfassung An Laborkulturen wurde das Zusammenwirken mehrerer ökologisch bedeutsamer Faktoren auf die Produktivität der Grünalgen Chlorella fusca var. vacuolata Shih et Krauss, Coelastrum proboscideum Bohlin und Chlamydomonas sp. untersucht. Mit Hilfe der Kombination von Starklicht sowie von DDT- und NaCl-Zusatz zur Nährlösung wurden Interaktionen natürlicher und anthropogener Faktoren erfaßt. Die Versuchsanstellung wurde dadurch den Freilandbedingungen möglichst angeglichen. DDT, das selbst keine Wachstumsdepressionen auslöste, verstärkte bei Chlamydomonas die Starklichtwirkung, bei Chlorella und Coelastrum die durch NaCl-Zusatz verursachte Wachstumshemmung. Kombinationseffekte zeigten sich auch bezüglich Starklichtschock und NaCl-Zusatz. Lang anhaltende und ausgeprägte Wachstumsverzögerungen wurden beim Zusammenwirken aller drei Faktoren bei jeder der untersuchten Arten beobachtet. Den technischen Assistentinnen Fräulein E. Konz und Frau C. Göls danken wir für die stets zuverlässige Mitarbeit bei der Durchführung der Versuche.
Article
A review of the literature supports the conclusion that, under some conditions, an increase of the rate of “apparent” respiration, as measured by gaseous exchange, may be induced by irradiation of various species of plants and types of plant tissues. In the present elementary state of our knowledge it can not be decided with certainty whether or not the observed stimulations are directly related to the “true” respiration. Despite the long-continued interest in this problem the results thus far available are almost entirely of a descriptive nature, and in no single case has there been presented, as yet, a satisfactory elucidation of the mechanism involved. From a consideration of the diverse conditions and types of material with which an alteration of the gaseous exchange has been observed, it seems altogether likely, however, that such an effect may be the common end result produced by a variety of phenomena.
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