Showing papers on "Photosynthesis published in 1968"
TL;DR: Partial defoliation leads to increased photosynthesis rates and increased levels of carboxylating enzymes, suggesting that in normal field conditions photosynthetic rates are limited by the levels ofCarboxylation enzymes and not by physical resistance to carbon dioxide diffusion in the leaf.
Abstract: Partial defoliation leads to increased photosynthetic rates and increased levels of carboxylating enzymes, suggesting that in normal field conditions photosynthetic rates are limited by the levels of carboxylating enzymes and not only by physical resistance to carbon dioxide diffusion in the leaf.
331 citations
TL;DR: The various aspects of the adaptation of plankton algae lo light and temperature are discussed and the shape of a light intensity-photosynthesis curve is shown to be an important means of describing the physiological adjustment of an algal population.
Abstract: The various aspects of the adaptation of plankton algae lo light and temperature are discussed. The shape of a light intensity-photosynthesis curve is shown to be an important means of describing the physiological adjustment of an algal population.
If the algae are not exposed to adverse influences such as poisons, pronounced nutrient deficiency or light shocks, the rate of real photosynthesis per mg chlorophyll a at 1 Klux (incandescent light) should be about 0.4–0.6 mg C/hour. Hence this rate presents an excellent means of judging the quality of experiments.
Experiments are presented where Chlorella pyrenoidosa was adapted to light intensities between 0.32 klux and 21 Klux. This alga adapts to different light intensities by varying the amount of pigments per cell. Algae grown at 1 Klux have about 10 times more chlorophyll per cell than those grown at 21 klux. Other species of algae—but by no means all—are shown to behave in the same way.
The problem of algal resistance to photo-oxidation at high light intensities is discussed. Adaplation is shown to he one of the mechanisms which make the algae resistent. “Chlorophyll inactivation” is another.
Experiments with the diatom Skeletonema costatum concerning adaptation to different temperatures have been performed. The fact that the alga has essentially the same rate of photosynthesis per cell at all light intensities at 20°C and 7°C, may be attributed to an increase of all the enzymes at the low temperature. The amount of protein per cell was twice as high at 7°C as at 20°C.
225 citations
TL;DR: The enzyme was isolated from leaves of tropical grasses that catalyses the reversible conversion of pyruvate, ATP and orthophosphate into phosphopyruvates, AMP and pyrophosphate and its role in photosynthesis is discussed.
Abstract: 1. An enzyme was isolated from leaves of tropical grasses that catalyses the reversible conversion of pyruvate, ATP and orthophosphate into phosphopyruvate, AMP and pyrophosphate. A requirement for Mg(2+) could not be replaced by Mn(2+) or Ca(2+). 2. By replacing orthophosphate with [(32)P]orthophosphate or with arsenate, evidence was provided that the orthophosphate consumed appears in pyrophosphate. 3. Without Mg(2+) or 2-mercaptoethanol the enzyme was rapidly and irreversibly inactivated. EDTA only partially replaced the requirement for the thiol compound. The enzyme was considerably more unstable at 0 degrees or when frozen than at 22 degrees . Even with the best conditions devised the enzyme lost about 25% of its activity every 3hr. 4. The activities of the enzyme in leaves of the tropical grasses sugar cane (Saccharum hybrid var. Pindar), maize (Zea mays) and sorghum (Sorghum vulgare) were comparable with their maximum photosynthesis rates. The enzyme was not detectable in leaf extracts from several other plants. 5. Its role in photosynthesis is discussed.
207 citations
TL;DR: The carbon dioxide compensation concentration of members of the Gramineae and a few other plants was determined with an infrared CO2 analyzer with results considered in relation to the greenhouse gas emissions of these plants.
Abstract: The carbon dioxide compensation concentration of members of the Gramineae and a few other plants was determined with an infrared CO2 analyzer. These results were then considered in relation to the new photosynthetic carboxylation pathway proposed by Hatch et al., rates of photosynthesis, grass systematics, leaf anatomy, and distribution of starch in the leaf. Plants possessing the new carboxylation pathway had low compensation values whereas those having the Calvin carboxylation reaction had high values. Low compensation plants also had a well-developed parenchyma bundle sheath containing a high concentration of chloroplasts which accumulated large amounts of starch. Little or no starch was present in the mesophyll cells. Cyperus was exceptional in that it also formed appreciable starch in the mesophyll. Those low compensation members of the Gramineae tested belonged either to the chloridoid–eragrostoid or the panicoid lines of evolution. A literature survey indicated that low compensation grasses have ph...
192 citations
TL;DR: It is concluded that low carboxydismutase activity probably is one of the factors that limit the capacity for light saturated photosynthesis in the shade plants.
Abstract: The activity of the photosynthetic enzyme carboxydismutase (ribulose-l,5-diphosphate carboxylase) was measured in leaf extracts of a number of higher plant species from habitats with greatly contrasting light intensities. Plants occupying sunny habitats and capable of light saturated rates of photosynthesis several times higher than those growing in the deep shade of redwood forests also have a considerably higher carboxydismutase activity. Thus, when expressed on the basis of total chlorophyll or even fresh weight, the enzyme activity is several times greater among the sun than among the shade species.
The comparatively low content of soluble protein in the shade plants indicates that their content of enzymes other than carboxydismutase also is low. Nevertheless, the activity of carboxydismutase even on the basis of soluble protein appears to be significantly higher in the sun than in the shade species.
It is concluded that low carboxydismutase activity probably is one of the factors that limit the capacity for light saturated photosynthesis in the shade plants.
191 citations
TL;DR: It was concluded that the small initial rise of the total rise curve did not reflect the photoreduction of Q, but rather the activation of this trapping center, and was analyzed in terms of a bimolecular reaction between Q and A.
184 citations
TL;DR: The analysis shows that chlorophyll a and fucoxanthin are the principal light absorbing pigments and that absorption by other carotenoids is very small.
Abstract: SUMMARY
A maximum growth rate with doubling time of 18 hr at 18 C could be maintained. Continuous cultures at about half maximum growth rate provided cells for study of pigments and photosynthesis. The light intensity curve of photosynthesis had no unusual features and showed light-saturated rates of 30-35 μl O2/mrn3-hr at 18 C. Pigment analysis showed chlorophylls a and c (a/c ratio = 4), fucoxanthin, β-carotene, and diadinoxanthin. Growth under red light (±660 mμ) altered pigments only by decrease in chlorophyll c to about one-half the content obtained under clear tungsten lamps. The large and anomalous spectral shift in fucoxanthin following organic solvent extraction runs confirmed, but efforts to isolate a native fucoxanthin were unsuccessful. Spectral analysis of acetone extracts and sonicated cell preparations allowed estimate of fractional absorption by each component pigment. The analysis shows that chlorophyll a and fucoxanthin are the principal light absorbing pigments and that absorption by other carotenoids is very small.
161 citations
TL;DR: The role of photosynthetic sulfur bacteria as primary producers in stagnant lakes having hydrogen sulfide is described in this paper, where the authors show that organic matter was produced by phytoplankton in the epilimnion and mainly by photosynthetically sulfur bacteria in the reducing zone.
Abstract: The role of photosynthetic sulfur bacteria as primary producers in stagnant lakes having hydrogen sulfide is described. Photosynthetic bacteria normally appear at the boundary layer of the oxidative and reductive zones, where H2S is present and the light intensity is lower than 10% of the surface value. The water of this layer was milky green or pink due to dense populations of Thiorhodaceae or Chlorobacteriaceae. The amount of photosynthetic bacterial biomass measured on a chlorophyll basis ranged from 100 to 828 mg/m3 for Chl-650, 60.7 to 79.5 mg/m3 for Chl-660, and 19.8 to 186 mg/m3 for BChl in the growing period from July to October.
In the lakes studied, organic matter was produced by phytoplankton in the epilimnion and mainly by photosynthetic sulfur bacteria in the reducing zone. The organic matter synthesized by these bacteria ranged from 9 to 25% of the total annual production in lakes rich in H2S and from about 3 to 5% in lakes poor in it.
155 citations
TL;DR: A simplified procedure permits the separation of spinach chloroplasts which retain the ability to catalyze the photosynthetic assimilation of carbon dioxide and its associated oxygen evolution.
Abstract: A simplified procedure (involving disruption in sorbitol-pyrophosphate mixtures) permits the separation of spinach chloroplasts which retain the ability to catalyze the photosynthetic assimilation of carbon dioxide and its associated oxygen evolution
151 citations
TL;DR: Concentrations of DDT as low as a few parts per billion in water reduced photosynthesis in laboratory cultures of four species of coastal and oceanic phytoplankton representing four major classes of algae, and in a natural phy toplanka community from Woods Hole, Massachusetts.
Abstract: Concentrations of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] as low as a few parts per billion in water reduced photosynthesis in laboratory cultures of four species of coastal and oceanic phytoplankton representing four major classes of algae, and in a natural phytoplankton community from Woods Hole, Massachusetts. Toxicity to diatoms increased as cell concentration decreased. This inhibition may be of ecological importance.
147 citations
TL;DR: A hypothesis is presented stating that the uniquie morphological and biochemical characters of these plants represent adaptations for efficient and rapid carbon fixation in environments where water stress frequiently limits photosynthesis.
Abstract: The C4-dicarboxylic-acid pathway of photosynthetic CO2 fixation found in tropical grasses has recently been demonstrated in members of the Amaranthaceae and Chenopodiaceae. In the tropical grasses this C02-fixation pathway is correlated with specialized leaf anatomy and chloroplast structure. This investigation was undertaken to determine if leaf cells of some representatives of these other families had structural features similar to those of tropical grasses. The leaf anatomy of Amaranthus edulis and a variety of Atriplex species is very similar and it resembles that of grasses such as sugar cane. Prominent bundle sheaths are surrounded by a layer of palisade cells. Bundle-sheath cells of Am. edulis have large chloroplasts containing much starch, but the chloroplasts have grana. The palisade cells have much smaller chloroplasts containing very little starch. The bundle-sheath cell chloroplasts of At. lentiformis have grana, their profiles tend to be ovoid, and they contain abundant starch grains. The palisade cell chloroplasts contain little starch and their profiles are discoid. The bundle-sheath cells of both species contain mitochondria which are much larger than those in the palisade cells. The chloroplasts in both types of cells in both species have a highly developed peripheral reticulum. This reticulum is composed of anastomosing tubules which are contiguous with the inner plastid membrane. The leaf anatomy and cell ultrastructure of these dicots are similar to those of the tropical grasses possessing this new photosynthetic carbon-fixation pathway. These morphological features are interpreted as adaptations for the rapid transport of precursors and end products of photosynthesis. A hypothesis is presented stating that the uniquie morphological and biochemical characters of these plants represent adaptations for efficient and rapid carbon fixation in environments where water stress frequiently limits photosynthesis. HATCH and Slack (1966) demonstrated that the photosynthetic carbon fixation pathway in sugar cane differs from the conventional Calvin cycle. After 1 sec in C'402, 93 % of the fixed radioactivity was found in oxaloacetate, malate, and aspartate. They have investigated carbon fixation pathways in a variety of monocotyledon and dicotyledon species, and the "cane-type" or C4-dicarboxylic acid pathway of photosynthetic carbon fixation has been found in species of the following genera of grasses: Zea, Sorghum, Paspalum, Axonopus, Digitaria, Chloris, Eragrostis (Hatch, Slack, and Johnson, 1967). A species of Cyperus also possessed this pathway. Phosphopyruvate carboxylase is considered to be the major photosynthetic C02-fixing enzyme in these taxa (Slack and Hatch, 1967). These grasses possess other features in common. They are characterized by their high rates of photosynthesis at high light IReceived 24 October 1967. This work was supported by a grant from Tate and Lyle, Ltd., and by NSF Grant GB-6066. The technical assistance of Janet Burr and Ian Price is gratefully acknowledged. intensities (Burr et al., 1957; Hesketh and Moss, 1963; El-Sharkawy and Hesketh, 1965), by their failure to "leak" respiratory CO2 during the light period (El-Sharkawy, Loomis, and Williams, 1967), and by low CO2 compensation values (Moss, 1962). In addition, Dr. Bruce Smith (Division of Geology, California Institute of Technology) has recently shown that these tropical grasses have much higher '3C/12C ratios than temperate grasses (personal communication). It has also been known for many years that the chloroplasts in the bundle-sheath cells of tropical grasses differed from the chloroplasts in the surrounding mesophyll cells. Rhoades and Carvalho (1944) demonstrated this in maize and sorghum on the basis of light microscopy, but the details of these dimorphic chloroplasts were only revealed by studies with the electron microscope. These were made on maize by Hodge, McLean, and Mercer (1955), on a variety of tropical grasses by Johnson (1964), and on sugar cane by Laetsch, Stetler, and Vlitos (1965). In these plants the mature chloroplasts in the promi[The JOURNAL for August (55: 745-874) was issued 1 August 1968] AMERICAN JOURNAL OF BOTANY, AVol. 55: No. 8, 1968
TL;DR: It is concluded that differentiation between plants from habitats with contrasting light intensities, whether unrelated species or ecotypos of the same species, probably involves the capacity of several component steps of the photosynthetic process.
Abstract: Measurements of the fraction of the incident light absorbed by diverse Solidago leaves revealed that differences in light harvesting capacity cannot explain the differences in efficiency of utilization of weak light in photosynthesis that have previously been shown to exist between sun and shade ecotypes when these have been grown in strong light and between identical clones of shade ecotypes when grown at different light intensities. Photosynthesis measurements at low and normal oxygen concentrations, provided no evidence that a different degree of inhibition of photo-synthetic CO2 uptake by atmospheric oxygen is responsible for the observed differences in photosynthetic efficiency, at low or high light intensities. These results support the conclusion that the markedly less efficient use of weak light by shaded habitat clones grown in strong as compared with weak light is caused primarily by damage to the photosystems, or to a site close to them. Measurements of Emerson enhancement and of light-induced absorbance changes provide some evidence that photoreaction II is more affected than I.
Enzyme extracts prepared from clones native to an exposed habitat were found to contain considerably higher activities of carboxydismutase (ribulosc-l,5-diphos-phate carboxylase) than from clones native to a shaded habitat when the plants were previously grown at a moderately high light intensity. Exposed habitat clones apparently have a genetically determined, higher capacity to produce the carboxyla-tion enzyme than shaded habitat clones. The high degree of correlation found when the light-saturated rate of CO2 uptake in vivo of a number of individual Solidago leaves is plotted against the carboxydismutase activities found in the extracts of these same leaves suggests that low carboxydismutase activity is one of the intrinsic properties responsible for the low capacity for light-saturated photosynthesis of clones from shaded habitats.
It is concluded from this and other investigations that differentiation between plants from habitats with contrasting light intensities, whether unrelated species or ecotypos of the same species, probably involves the capacity of several component steps of the photosynthetic process.
TL;DR: Measurements were made of growth, pigmentation, photosynthesis, respiration, quinone Hill reaction, cell morphology, and structure as a function of growth light intensity for various algae.
Abstract: SUMMARY
Measurements were made of growth, pigmentation, photosynthesis, respiration, quinone Hill reaction, cell morphology, and structure as a function of growth light intensity for various algae. These processes showed varying degrees of dependency upon light intensity and are discussed with reference to algal classification. Eighteen algae, examples from 10 taxonomic divisions, were studied.
TL;DR: An experiment in which changes in the level of ATP were observed on addition of CO 2 shows that ATP and ADP can apparently re-enter the chloroplasts and be used metabolically.
TL;DR: The effect of O( 2) on apparent photosynthesis could be ascribed to a combination of stimulation of CO(2) production during photosynthesis, and inhibition of photosynthesis itself.
Abstract: The effect of 21% O(2) and 3% O(2) on the CO(2) exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2 degrees and 43 degrees , CO(2) concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O(2) compared to 3% O(2). The degree of inhibition increased with increasing temperature and decreasing CO(2) concentration. Light intensity did not alter the effect of O(2) except at light intensities or CO(2) concentrations near the compensation point. At high CO(2) concentrations and low temperature, O(2) inhibition of apparent photosynthesis was absent. At 3% O(2), wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30 degrees , and a CO(2) compensation point of less than 0.0005% CO(2). The effect of O(2) on apparent photosynthesis could be ascribed to a combination of stimulation of CO(2) production during photosynthesis, and inhibition of photosynthesis itself.
TL;DR: The low fluorescence yield of P870 shows that energy reaching this pigment is quenched rapidly, and the high quantum efficiency for P870 oxidation shows that most of this quenching is due to the initiation of photochemistry.
Abstract: Photosynthetic bacteria contain bacteriochlorophyll (BChl) that absorbs light and delivers the resulting singlet excitation energy to photochemical reaction centers.' The reaction centers, which have been isolated in a form free of lightharvesting BChl,'-3 contain a photochemically specialized BChl which in Rhodopseudomonas spheroides is called P870 after its absorption maximum near 870 nm. Excitation energy reaching the reaction centers causes oxidation (bleaching) of P870 and, presumably, reduction of an electron acceptor. Another specialized BChl, P800, is associated with P870 in the reaction centers and shows a band shift to shorter wavelengths when P870 is bleached. The oxidation of P870 occurs with a quantum efficiency close to 100 per cent whether the light is absorbed by light-harvesting BChl in chromatophores4 5 or by either P800 or P870 in reaction center preparations.6 Cells or chromatophores of photosynthetic bacteria emit BChl fluorescence when illuminated. This fluorescence comes from the light-harvesting BChl and competes with the utilization of energy at the reaction centers.\" 7 The yield of fluorescence from P870, measured in the absence of light-harvesting BChl, is small compared with that from light-harvesting BChl measured in chromatophores.8 The low fluorescence yield of P870 shows that energy reaching this pigment is quenched rapidly, and the high quantum efficiency for P870 oxidation shows that most of this quenching is due to the initiation of photochemistry. The lifetime of an excited state of a molecule is indicated by the yield of fluorescence corresponding to that state. If the only avenue for de-excitation were the radiative one, the yield would be 100 per cent and the lifetime would assume a maximum value called the intrinsic lifetime, To. If de-excitation can occur by other competing processes such as a photochemical quenching, both the lifetime r and the fluorescence quantum yield of will be reduced in proportion:
TL;DR: It was concluded that maize does not evolve appreciable quantities of CO(2) in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize.
Abstract: A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed (14)CO(2) in light in a rapid stream of CO(2)-free air at 30 degrees to 35 degrees . In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the (14)CO(2) output in the dark. In maize, photorespiration is only 2% of that in tobacco.The importance of open leaf stomata, rapid flow rates of CO(2)-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the (14)CO(2) evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by alpha-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35 degrees the quantity of (14)CO(2) released in the assay may represent only 33% of the gross (14)CO(2) evolved in the light, the remainder being recycled within the tissue.It was concluded that maize does not evolve appreciable quantities of CO(2) in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO(2) uptake at the normal concentrations of CO(2) found in air and at higher light intensities.
TL;DR: An oxygen requirement of isolated intact chloroplasts reducing PGA and nitrate was indicated by lower reaction rates and faster decay of activity under nitrogen than under air.
Abstract: Oxygen was taken up by both intact and broken chloroplasts when catalase was posioned. In confirmation of other work we found that oxygen enters the electron transport chain of isolated chloroplasts by oxidizing the primary photoreductant of system I. In isolated intact chloroplasts this reaction proceeds in addition to oxygen evolution by PGA reduction. The reductant produced by photosystem II does not react with oxygen at a significant rate. In normal leaves oxygen depresses chlorophyll fluorescence. However, this depression does not take place in DCMU poisoned leaves or in a mutant having a nonfunctional photosystem II; furthermore, another mutant with a weakly functioning photosystem I gave only a very small fluorescence depression with oxygen. This shows that the site of interaction of oxygen is at the reducing end of the electron transport chain. This view is supported by the extent of the fluorescence depression in leaves as a function of oxygen concentration which is very similar to the oxygen dependence of oxygen uptake by isolated chloroplasts. An oxygen requirement of isolated intact chloroplasts reducing PGA and nitrate was indicated by lower reaction rates and faster decay of activity under nitrogen than under air.
TL;DR: Measurements of photosynthetic rate suggest that there is a correlation between decay of photosynthesis and survival after UV exposure and that the UV induced decay in photosynthesis is reversed by the identical photoreactivation conditions that increase the survival level.
Abstract: The effects of UV irradiation (254 mμ) on a coccoid blue-green alga Agmenellum quadruplicatum, Strain PR-6, have been examined in terms of the survival curve and measurement of short time photosynthetic rates. From study of survival evidence has been found for a strong photoreactivation centered near 430 mμ. Measurements of photosynthetic rate suggest that there is a correlation between decay of photosynthesis and survival after UV exposure. The UV induced decay in photosynthetic activity is reversed by the identical photoreactivation conditions that increase the survival level. The photosynthetic data are interpreted as demonstrating a photoreactivation of photosynthesis in blue-green algae.
TL;DR: The kinetics of reversal are characteristic of the intermediate used, but, in each instance, the onset of oxygen evolution is accompanied by a carbon dioxide fixation and except with 3-phosphoglycerate the stoicheiometry is close to unity.
Abstract: 1. The orthophosphate inhibition of photosynthesis by isolated spinach chloroplasts can be reversed by 3-phosphoglycerate, dihydroxyacetone phosphate, glyceraldehyde 3-phosphate, fructose 6-phosphate and fructose 1,6-diphosphate. 2. Metabolically related compounds such as ribulose 1,5-diphosphate, glucose 6-phosphate, 6-phosphogluconate and phosphoenolpyruvate are ineffective. 3. The kinetics of reversal are characteristic of the intermediate used, but, in each instance, the onset of oxygen evolution is accompanied by a carbon dioxide fixation and except with 3-phosphoglycerate the stoicheiometry is close to unity. 4. The nature of orthophosphate inhibition and its reversal is discussed in relation to metabolic control of photosynthesis.
TL;DR: Analysis of non-aqueous fractions of leaves indicates that carbonic anhydrase is a cytoplasmic enzyme in plants with C 4 -dicarboxylic acid pathway, whereas in plantsWith only the Calvin cycle the enzyme is located in the chloroplasts.
TL;DR: It was concluded that manganese functions specifically in the photochemical complex E of Photosystem II, with increasing deficiencies, loss of chloroplast-bound Mn led to decreased flash yield of O 2 and increasing quantum requirement of photosynthesis and quinone photoreduction.
TL;DR: Isolated pea chloroplasts undergo both cyclic and non-cyclic electron flow, and ADP-governed photosynthetic control' was shown to be dependent on the intactness of the chloroplast.
Abstract: Isolated pea chloroplasts undergo both cyclic and non-cyclic electron flow Both processes are coupled to photophosphorylation During non-cyclic flow the rate of oxygen production showed ADP-governed ;photosynthetic control' analogous to respiratory control of isolated mitochondria Measurements of ADP/O and photosynthetic control ratios yielded values of 1-13 and 2-57 respectively ;Photosynthetic control' was shown to be dependent on the intactness of the chloroplasts
TL;DR: This chapter describes the organized structure of photosynthetic apparatus of bacterial system and describes the structure and location of Chromatophore material, isolation and composition of purified chromatophores, and formation of the photosynthesis apparatus.
Abstract: Publisher Summary The unique physiological characteristic of the photosynthetic bacteria is their ability to grow anaerobically in the light, a property conferred on them by their photosynthetic pigment system Bacterial processes generally require an exogenous reductant The different genera of photosynthetic bacteria characteristically use reduced inorganic sulfur compounds, hydrogen, or organic substrates as reductant and also vary with respect to their ability to use carbon dioxide as sole carbon source This chapter describes the organized structure of photosynthetic apparatus of bacterial system It describes the structure and location of chromatophore material, isolation and composition of purified chromatophores, and formation of the photosynthetic apparatus Bacteria like other photosynthetic forms of life have both carotenoids and chlorophylls Carotenoids essentially harvest light at wavelengths, which are not absorbed by chlorophyll and also protect cells from photodynamic oxidation reactions Bacteriochlorophyll a is the most widely distributed type of chlorophyll recognized in photosynthetic bacteria Chromatophores represent a specialized structure that essentially houses the photosynthetic pigments and catalyzes photophosphorylation and photoreduction reactions
TL;DR: In genera from two dicotyledonous families, Amaranthaceae and Chenopodiaceae, the occurrence of the C 4 -dicarboxylic acid pathway of photosynthesis correlates with low ribulose diphosphate carboxylase activity, high activities of phosphopyruvate car boxylase and phosphate synthetase, a unique type of leaf anatomy, and high photosynthesis rates.
TL;DR: The behaviour of certain Amaranthus species behave more like the tropical grasses such as corn than like other dicotyledonous species, and a characterization of its photosynthetic responses to light, carbon dioxide and temperature is of interest.
Abstract: The primary productivity of a plant community depends largely on the activity of the individual photosynthetic elements of the foliage canopy. Although an extensive literature exists on the photosynthetic capabilities of individual leaves, it is only recently that such data have been used successfully in the interpretation of community productivity (de Wit 1965; Monteith 1965; Duncan et al. 1967). In these studies, usually aided by electronic computers, the illumination of each leaf has been assessed and then the net photosynthesis resulting from that illumination has been summed for an entire community. Such simulations are highly dependent upon the physiological data which are supplied to the computer, and one needs to consider environmental variations as well as the manner in which the plants adapt to particular conditions within the canopy. An important aspect of such adaptations is that the photosynthetic capability of a leaf, as well as its activity, may vary according to its illumination within a canopy; thus photosynthetic capabilities may be assessed best from measurements with leaves adapted to various light environments. Bjorkman (1965, 1966) has shown with Solidago and other species that adaptation to a specific light environment may involve significant changes in the relative contributions of photosystems I and II and other basic reactions in photosynthesis. In addition, Ludwig, Saeki & Evans (1965) and McCree & Troughton (1966) have recently shown that the adaptation of leaves to different illumination levels also results in marked changes in their rates of dark respiration. From recent work it has become evident that interspecific and environmentally induced variations in the compensation light intensities, and the maximum photosynthetic rates of individual leaves, all depend substantially on variations in the rates of respiration, both in light and in dark (El-Sharkawy & Hesketh 1965; El-Sharkawy, Loomis & Williams 1967; Duncan et al. 1967). The very large photosynthetic rates of several tropical grasses are associated with the failure of their leaves to release respiratory CO2 when sun-adapted plants are exposed to light while maintained in an atmosphere free of CO2 (El-Sharkawy & Hesketh 1965). This contrasts with the behaviour of a number of dicotyledonous species which have much smaller maximum photosynthetic rates associated with a marked release of CO2 into C02-free air during illumination. In further studies of dicotyledonous species, El-Sharkawy et al. (1967) discovered that in respect to photosynthesis and respiration, certain Amaranthus species behave more like the tropical grasses such as corn than like other dicotyledonous species. This report is concerned with the behaviour of one of these amaranths, A. edulis, the grain amaranth. A characterization of its photosynthetic responses to light, carbon dioxide and temperature is of interest because of the potential of the species as research material for studies on maximization of primary productivity in terrestrial plant communities. The grain amaranth is a tall, erect, annual herb, and in open stands it may branch at all nodes. At Davis, California, it grows well as a summer annual and reaches a height of * Present address: Ministry of Agriculture, Cotton Production Section, Giza Station, Cairo, Egypt.