Showing papers on "Photosynthesis published in 1972"

Photooxidative Death in Blue-Green Algae

Abstract: When incubated in the light under 100% oxygen, wild-type blue-green algae (Anacystis nidulans, Synechococcus cedrorum) die out rapidly at temperatures of 4 to 15 C, and at 35 C (or at 26 C in the case of S. cedrorum) in the absence of CO(2). Photosynthesis is impaired in these cells long before they die. Blocking of photosystem II at high temperatures in the presence of CO(2) sensitizes the algae to photooxidative death. Photooxidative death and bleaching of photosynthetic pigments are separable phenomena. Photooxidative conditions were demonstrated in Israeli fish ponds using A. nidulans as the test organism during dense summer blooms, when dissolved CO(2) is low, and in winter, when water temperatures generally drop below 15 C. This finding suggests that photooxidative death may be responsible for the sudden decomposition of blue-green blooms in summer, and may be a factor in the absence of blue-green blooms in winter.

Natural Abundance of the Stable Isotopes of Carbon in Biological Systems

Abstract: About 99% of all carbon is the 12C isotope while 1% is 13C. The other isotopes of carbon are, by comparison, extremely rare. For instance, only about one atom in every 1012 carbon atoms is 14C. The precise ratio of the isotopes will vary depending on the material analyzed. Limestones, atmospheric C02, marine algae, and land plants each possess characteristic 13C/12C ratios, differing slightly from one another. The lowest ratio so far observed is for carbon from ancient blue-green algal mats (Kaplan and Nissenbaum, 1966) and the highest for carbonate carbon from meteorites (Clayton, 1963). Fractionation of plant carbon is brought about primarily by carbon dioxide assimilation in photosynthesis and is due to preferential utilization of 12C and exclusion of 13C. Curiously enough, it has been found recently (Tregunna et al., 1970) that higher plants which fix carbon dioxide via the Calvin cycle pathway differ in 13C/12C ratios from plants which fix carbon dioxide via the C4-dicarboxylic acid pathway. Thus, it is now possible to determine whether a given sample of sucrose was synthesized in sugarcane or in sugar beet. While it is the aim of this paper to discuss a few recent studies on naturally-occurring 13C/12C ratios of biological materials, it is pertinent to note that the subject has been reviewed from a geochemical viewpoint (Bowen, 1966; Degens, 1969; Kroepelin, 1966; McMullen and Thode, 1963; Schwarcz, 1969). The various isotopic species of an element differ slightly in chemical properties from one another. Just as the chemical properties of different compounds determine their formation under various conditions, so the chemical properties of different isotopic species of the compounds will determine how the isotopic abundances distribute themselves in nature. Thus substitution

Photosynthetic and dark carbon metabolism in unicellular blue-green algae.

Abstract: 0946 09 1. The kinetics of 14CO2 incorporation into cellular intermediates was used to determine the primary pathway of carbon fixation by four genetically diverse unicellular blue-green algae. In each case label was first detected in 3-phosphoglycerate and then in compounds of the reductive pentose cycle. 2. A light to dark transition evoked the same response in all four strains: Immediate cessation of biosynthesis, rapid increase in the concentration of 6-phosphogluconate and changes in the concentrations of sugar mono- and diphosphates. On the other hand, after the first few seconds of dark incubation little or comparatively slow change was noted in the concentrations of 3-phosphoglycerate, phosphoenolpyruvate, citrate, aspartate, and glutamate. 3. For one strain (aphanocapsa 6308) an experiment using both 32P and 14CO2 as tracers revealed comparatively rapid turnover of metabolites common to the oxidative pentose cycle during dark incubation. Much slower turnover of labeled carbon was found in other metabolites of glycolysis and the biosynthetic portions of the tricarboxylic acid cycle. 4. During dark incubation of Aphanocapsa 6308 the concentration of adenosine triphosphate decreased to approximately 50% of the photosynthetic value within the first 50 sec. In the same period, adenosine diphosphate nearly doubled in concentration. By 4 min after the beginning of the dark period, the steady-state levels of the two adenylates had been restored to photosynthetic levels.

The Cupric Ion as an Inhibitor of Photosynthetic Electron Transport in Isolated Chloroplasts

Abstract: Strong inhibition of uncoupled photosynthetic electron transport by Cu(2+) in isolated spinach chloroplasts was observed by measuring changes in O(2) concentration in the reaction medium. Inhibition was dependent not only on the concentration of the inhibitor, but also on the ratio of chlorophyll to inhibitor. Binding of Cu(2+) to the chloroplast membranes resulted in removal of Cu(2+) from solution. When chloroplasts were exposed to preincubation in light, there was increased inhibition as a result of Cu(2+) binding to inhibitory sites. Preincubation in the dark resulted in Cu(2+) binding to noninhibitory sites and decreased inhibition. The degree of inhibition was lower at low light intensities than at high light intensities.When the photosystems were assayed separately, photosystem I was more resistant to inhibition than photosystem II. The most sensitive site to the inhibitor was the oxidizing side of photosystem II.

Salt responses of carboxylation enzymes from species differing in salt tolerance.

Abstract: This paper reports effects of salts on in vitro activity of phosphoenolpyruvate carboxylase and ribulose-1,5-diphosphate carboxylase, isolated from species differing in salt tolerance.Inhibition of phosphoenolpyruvate carboxylase by the inorganic salts KCl, NaCl, and Na(4)SO(4) depended on the source of the enzyme. Phosphoenolpyruvate carboxylase isolated from leaves of C(4) plants was extremely sensitive to inorganic salts, whereas the enzyme extracted from roots of C(4) plants or from both shoots and roots of C(3) plants was much less sensitive. Ribulose-1,5-diphosphate carboxylase was less salt-sensitive than the phosphoenolpyruvate carboxylases. Differences in salt sensitivity of carboxylases were observed over a wide pH range. The results suggest substantial physical-chemical differences between phosphoenolpyruvate carboxylases functioning in photosynthesis and in CO(2) dark fixation.Among C(4) species, phosphoenolpyruvate carboxylase from halophytic species was more salt-sensitive than that from a salt-sensitive species. This anomaly, between in vitro response of enzymes and growth response of the plants, is briefly discussed.

Photosynthesis by isolated chloroplasts. Inhibition by DL-glyceraldehyde of carbon dioxide assimilation.

Abstract: Photosynthetic carbon assimilation and associated CO(2)-dependent O(2) evolution by chloroplasts isolated from pea shoots and spinach leaves is almost completely inhibited by 10mm-dl-glyceraldehyde. The inhibitor is without appreciable effect on photosynthetic electron transport, photophosphorylation, the carboxylation of ribulose 1,5-diphosphate or the reduction of 3-phosphoglycerate, but apparently blocks the conversion of triose phosphate into ribulose 1,5-diphosphate.

Energy Conversion and Generation of Reducing Power in Bacterial Photosynthesis

Abstract: Publisher Summary Bacterial and green-plant photosynthesis share a number of basic features, but are distinctly different in respect to one another. The physiological property of the photosynthetic bacteria that makes the bacteria unique in the biological world states the ability of bacteria to grow rapidly under anaerobic conditions, using light as the ultimate energy source. The photosynthetic bacteria display a remarkable metabolic diversity and versatility. Essentially, in the anabolic phase of cell growth, appropriate organic intermediates and monomers are produced from the carbon and nitrogen sources of the external medium and these are utilized for the synthesis of proteins, nucleic acids, lipids, carbohydrates, and various other complex cellular substances. Synthesis of the intermediates and monomers requires energy in the form of ATP and reducing power—primarily as reduced nicotinamide nucleotide. The chapter describes photophosphorylation, generation of net reducing power, comparison of energy metabolism and electron-transfer patterns in photosynthetic bacteria and clostridia, and the regulatory mechanisms.

[32] Inhibition of photosynthetic electron transport and photophosphorylation☆

Abstract: Publisher Summary This chapter reviews the results of inhibition studies in isolated chloroplasts and bacterial “chromatophores.” The chloroplasts employed are usually naked lamellae from spinach ( Spinacia oleracea L.), and the chromatophores are from Rhodospirillum rubrum or Rhodopseudomonas and Chromatium . Most of the chloroplast inhibitions are of a general nature affecting chloroplasts from all plants in a similar way. Substances or treatments that inhibit electron transport, regardless of its nature, act directly on some oxidoreduction step in the electron transport chain. The mode of action of a typical electron transfer inhibitor, 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU) is illustrated in the chapter. The basal nonphosphorylating electron transport, the phosphorylating electron transport, and phosphorylation are similarly inhibited. A cyclic photosynthetic electron transfer chain, which appears to be the main energy-generating system, is demonstrated in all kinds of photosynthetic bacteria examined. In facultative phototrophs, the cyclic photosynthetic chain is connected with an aerobic respiratory chain, which itself can support, by means of oxidative phosphorylation, cell growth in the dark.

Tissue Water Potential, Photosynthesis, C‐Labeled Photosynthate Utilization, and Growth in the Desert Shrub Larrea divaricata Cav.

Abstract: Tissue water potential is the most important factor throughout the seasons controlling phenological events, photosynthesis, and productivity of Larrea divaricata growing in Deep Canyon near Palm Desert, California. Growth of reproductive structures was initiated at the time of highest tissue water potential and ceased as water potential decreased. Percentage foliation correlated strongly with dawn water potential (r = 0.89). The elongation rate of stems and the rate of node production were both dependent on tissue water potential. Leaf growth and node growth proceeded at varying rates throughout the year, providing a continuous sink for photosynthates. Photosynthesis rates ranged from 9.02 mg CO2 incorporated per day per gram dry weight of leaf tissue in September to an estimated 74.7 mg CO2 in early February. Net photosynthesis and relative productivity correlated very strongly with dawn water potential (r = 0.93 and r = 0.97, respectively). Larrea plants were labeled at 1— to 2—month intervals with photosynthetically incorporated 14CO2to determine the utilization in growth and storage of photosynthate fractions produced at various times throughout the year. Tissue was subsampled at similar intervals, and the activity in various metabolic compounds (sugar, starch, lipid, organic acid, amino acid, protein, cellulose, and cell—wall materials) was analyzed. The utilization of photosynthates in the various fractions was similar in all seasons. No appreciable mobilization into and out of storage materials was apparent. Never dormant, Larrea remains metabolically active and forms new tissue throughout the year. This growth pattern may be an important adaptation allowing Larrea to exist in a wide range of geographical and climatic areas, and, perhaps owing to the species' tropical affinities, it might have been a preadaptation to the desert environment.

The Development of Photosynthesis in a Greening Mutant of Chlorella and an Analysis of the Light Saturation Curve

Abstract: Photosynthetic oxygen evolution considerably precedes the rise in chlorophyll during the greening of a yellow mutant of Chlorella vulgaris. Dark-grown cells required 20 times more light to saturate photosynthesis than light-grown or normal cells. The chlorophyll appears to add first to active reaction centers, then to fill in a more general antenna. The carotenoid pigments seem to add more randomly to the reaction centers. The shape of the light saturation curves can be explained with the assumption that an excitation in the antenna can reach several reaction centers. The efficiency of the total unit is constant during the greening process.

Inhibition of Photosystem II in Isolated Chloroplasts by Lead

Abstract: Inhibition of photosynthetic electron transport in isolated chloroplasts by lead salts has been demonstrated Photosystem I activity, as measured by electron transfer from dichlorophenol indophenol to methylviologen, was not reduced by such treatment However, photosystem II was inhibited by lead salts when electron flow was measured from water to methylviologen and Hill reaction or by chlorophyll fluorescence Fluorescence induction curves indicated the primary site of inhibition was on the oxidizing side of photosystem II That this site was between the primary electron donor of photosystem II and the site of water oxidation could be demonstrated by hydroxylamine restoration of normal fluorescence following lead inhibition

On nitrogen deficiency in tropical pacific oceanic phytoplankton. ii. photosynthetic and cellular characteristics of a chemostat-grown diatom1

Abstract: R-BSTRACT Cells of the tropical Pacific diatom, Chaetoceros gracilis, were grown in a nitrogenlimited chemostat at varying percentages of the maximum growth rate, harvested, and photosynthetic and cellular parameters measured. Assimilation ratio (photosynthesis at light saturation per unit chlorophyll) increased with increasing growth rate. Cellular C : chlorophyll ratios also decreased with increasing growth rate, but carotenoid : chlorophyll ratios showed no obvious trend. The C : N ratio decreased and chlorophyll: cell increased with increasing growth rate. Steady-state cell numbers were not constant at different growth rates but decreased as the growth rates increased. Growth rates secmcd to be controlled by internal supplies of nitrogen and the apparent half saturation constant, K’, , decreased with increasing-growth rate.

Measurement of Hill reactions and photoreduction.

Abstract: Publisher Summary This chapter discusses the measurement of hill reactions and photoreduction. R. Hill discovered that a leaf homogenate would evolve oxygen when illuminated in the presence of a ferric salt. After the successful preparation of intact chloroplasts, it could be shown that the oxygen evolution system resides in the green particulate fraction obtained from intact chloroplasts by osmotic shock and that the CO 2 -fixation system can be separated from the light-dependent reactions of photosynthesis. The particulate fraction—the thylakoid system of whole chloroplasts is able to catalyze two types of photosynthetic reactions: photophosphorylation and photosynthetic reduction of an electron acceptor concomitant with oxygen evolution. A Hill reaction is defined as the photoreduction of an electron acceptor at the expense of water, which is oxidized to oxygen. The final Hill acceptor in photosynthesis in vivo is CO 2 . The chloroplasts are now accepted as the physiological Hill reaction is the photoreduction of nicotinamide adenine dinucleotide phosphate (NADP). Several redox reactions and redox carriers besides the actual light-accepting pigments are localized in the thylakoid system of the chloroplasts, and participate in photosynthetic NADP reduction at the expense of water photo-oxidation.

Photorespiration and Nitrogenase Activity in the Blue-Green Alga, Anabaena cylindrica

Abstract: Oxygen uptake in the light (photorespiration) by the nitrogen-fixing blue-green alga Anabaena cylindrica may be up to twenty times the dark respiration rate. The rate of uptake in the light increases linearly with increasing p O 2 while dark respiration is saturated at a p O 2 near 0.05 atm. Photorespiration is inhibited rapidly and completely by DCMU (3 x 10 -5 m) but KCN (10 -4 m) has little effect. Exogenously supplied hydroxyethane sulphonate (10 -5 m), an inhibitor of glycollate oxidase activity, and glycollate do not affect respiration, although 14 C-labelled glycollate is assimilated in the light and in the dark. Photorespiration is highly sensitive to p CO 2 and to NaHCO 3 concentration and approaches true photosynthetic oxygen production at the CO 2 compensation point of 10 parts/10 6 . A CO 2 concentration of 0.02 atm completely inhibits photorespiration whereas true photosynthesis is scarcely affected. Conditions which stimulate photorespiration (low p CO 2 and high p O 2 ) progressively inhibit acetylene reduction. In short-term studies DCMU inhibits acetylene reduction under condi­tions which stimulate photorespiration but has little effect under conditions which inhibit photorespiration. The results suggest that photorespiration and nitrogenase activity com­pete indirectly for reducing power and that at least one mechanism of oxygen inhibition of nitrogenase activity is via a stimulation of photorespiration.

Plants under climatic stress

Abstract: Summary The composition of the atmosphere influenced the apparent photosynthetic rate of Sorghum bicolor and the degree of permanent damage to the photosynthetic capacity of the leaves when plants were transferred to low-temperature, high-light (10° C; 170 W m-2) environmental stress. High CO2 (1000 μl/l) or low O2 (3%) both partially protect the plants compared to normal atmospheric levels, while low CO2 (30 μl/l) or O2 (50%) enhanced the damaging effects of stress. Oxygen levels are the more significant in control of permanent photosynthetic damage.

Endogenous inorganic carbon sources in plant hotosynthesis

Abstract: Summary The quantity of CO2 arising from photorespiration in angiosperms and in algae has been estimated. Much of such CO2 arises from the metabolism of glycolate so that estimates are based on the rate of formation of glycolate and the rate at which it is metabolized (Table 1). The total CO2 production in leaves or algae in the light can then be taken as equal to the photorespiratory CO2 plus the CO2 produced by‘dark’ respiratory pathways. Methods of estimating CO2 release from illuminated green tissues are considered and the rate of decarboxylation deduced from biochemical evidence of substrate turnover is compared with the observed rate of CO2 release; the difference between these values is reassimilation (Table 1). In angiosperms with the PGA pathway, in air, reassimilation is never complete and ranges from o to 0.6 of the endogenous CO2 production. This implies that the resistance to refixation is as great or greater than the resistance to loss of endogenous CO2 to the medium and is in accord with the relative values of these resistances based on other evidence. In law oxygen environment less glycolate is produced and hence less photorespiratory CO2; the resistance to refixation is smaller and so fractional reassimilation in increased. Unicellular algae have the PGA pathway and some appear to have more efficient reassimilation than the corresponding angiosperms. The special problems of metabolism in four carbon acid plants are discussed. Such plants show essentially complete reassimilation since they do not lose CO2 when illuminated. In their leaves the resistance to escape of endogenously produced CO2 must be very much greater than the resistance to refixation. The low resistance to refixation is probably related to high levels of CO2 in chloroplasts which are generated by the‘CO2-pump’ rather than to any peculiarities of carboxydismutase. The importance of reassimilation is discussed in relation to the influence of CO2 on various aspects of metabolism, to isotopic discrimination in CO2 fixation and to the mechanism of the use of bicarbonate in photosynthesis.

Effect of far red light and inhibitors on nitrogen fixation and photosynthesis in the blue-green alga Anabaena cylindrica

Abstract: Experiments on the relationship between nitrogen fixation and photosynthesis in intact Anabaena cylindrica are reported.

Estimation of the Transport and Carboxylation Components of the Intracellular Limitation to Leaf Photosynthesis

Abstract: A model is presented which enables gas exchange data to be used to partition the intracellular resistance to leaf photosynthesis into carboxylation and transport components. A basic assumption is that the over-all kinetics of the carboxylation reaction fit the Michaelis-Menten equation. The model was tested for cotton ( Gossypium hirsutum L., var. Deltapine Smoothleaf), where photorespiration was suppressed by using gas mixtures containing less than 1.5% oxygen. It was concluded that the transport resistance formed the major component of the intracellular resistance for the plants studied. However, in some cases the major intracellular factor limiting photosynthesis, at an ambient CO 2 concentration of 600 ng cm −3 , was the carboxylation system, which was close to saturation.

Symbiotic chloroplasts; their photosynthetic products and contribution to mucus synthesis in two marine slugs

Abstract: 1. The products of photosynthetic 14CO2 fixation by symbiotic chloroplasts in the marine sacoglossan opisthobranch gastropods Tridachia crispata (Morch) and Tridachiella diomedea (Bergh) were compared with those of the siphonous green alga Caulerpa sertularioides.2. After six hours photosynthesis in NaH14CO3, the distribution of 14C in organic compounds in the two slugs was similar, but different from that in the plant.3. The major soluble 14C-labelled carbohydrates found were glucose and sucrose in the plant and glucose and galactose in the slugs.4. The plant contained appreciable 14C-galactolipids, while little 14C could be detected in galactolipids in chloroplasts in the animals. In both slugs and alga large quantities of 14C were incorporated into polysaccharide.5. After pulse-labelleing for one hour, 14C-galactose was the major soluble carbohydrate detected in Tridachia. Subsequently, the galactose decreased with a concomitant increase in 14C-glucose. Thereafter maximum 14C-glucose was detected in se...

The Appearance and Development of Photosynthetic Activity in Etiolated Barley Leaves and Isolated Etio-chloroplasts

Abstract: The appearance and development of the oxygen exchanging capacity of greening barley leaves were measured using a manometric technique and an oxygen race electrode. An oxygen evolution could first be detected after one hour of greening. During the first hour of greening a light-dependent oxygen uptake was observed. The oxygen evolving capacity, calculated on a chlorophyll weight basis, showed a fast rise in activity during the first hours of greening. A maximal activity was reached after 5 to 10 hours of greening; the oxygen evolution then declined. Using oxygen electrodes different aspects of the electron transport in etio-chloroplasts prepared from the greening barley leaves were also investigated. The activity in photosystem I and II, as well as the cooperation between the two photosystems, were studied by measuring the oxygen exchange from the etio-chloroplasts in the absence and presence of added oxidants and reductants. An activity in photosystem I could be detected already after 5 minutes of greening. The activity of photosystem I, when calculated on a chlorophyll basis, had the same appearance as the oxygen evolution from the intact plant material. An activity in photosystem II and a cooperation between the two photosystems were first detected after 3 hours of greening. After about 15 hours of greening a cooperation corresponding to that from chloroplasts prepared from normal green leaves was observed.