Physiological studies on acid metabolism. 5. Effects of carbon dioxide concentration on phosphoenolpyruvic carboxylase activity

Control of the circadian rhythm of carbon dioxide assimilation in Bryophyllum leaves by exposure to darkness and high carbon dioxide concentrations

The circadian rhythm of CO2 assimilation in detached leaves of Bryophyllum fedtschenkoi at 15° C in normal air and continuous illumination is inhibited both by exposure to darkness, and to an atmosphere enriched with 5% CO2. During such exposures substantial fixation of CO2 takes place, and the malate concentration in the cell sap increases from about 20 mM to a constant value of 40-50 mM after 16 h. On transferring the darkened leaves to light, and those exposed to 5% CO2 to normal air, a circadian rhythm of CO2 assimilation begins again. The phase of this rhythm is determined by the time the transfer is made since the first peak occurs about 24 h afterwards. This finding indicates that the circadian oscillator is driven to, and held at, an identical, fixed phase point in its cycle after 16 h exposure to darkness or to 5% CO2, and it is from this phase point that oscillation begins after the inhibiting condition is removed. This fixed phase point is characterised by the leaves having acquired a high malate content. The rhythm therefore begins with a period of malate decarboxylation which lasts for about 8 h, during which time the malate content of the leaf cells must be reduced to a value that allows phosphoenolpyruvate carboxylase to become active. Inhibition of the rhythm in darkness, and on exposure to 5% CO2 in continuous illumination, appears to be due to the presence of a high concentration of CO2 within the leaf inhibiting malic enzyme which leads to the accumulation of high concentrations of malate in the leaf cells. The malate then allosterically inhibits phosphoenolpyruvate carboxylase upon which the rhythm depends. The results give support to the view that malate synthesis and breakdown form an integral part of the circadian oscillator in this tissue.

Minor Physiological Response to Elevated CO(2) by the CAM Plant Agave vilmoriniana

One-year-old plants of the CAM leaf succulent Agave vilmoriniana Berger were grown outdoors at Riverside, California. Potted plants were acclimated to CO(2)-enrichment (about 750 microliters per liter) by growth for 2 weeks in an open-top polyethylene chamber. Control plants were grown nearby where the ambient CO(2) concentration was about 370 microliters per liter. When the plants were well watered, CO(2)-induced differences in stomatal conductances and CO(2) assimilation rates over the entire 24-hour period were not large. There was a large nocturnal acidification in both CO(2) treatments and insignificant differences in leaf chlorophyll content. Well watered plants maintained water potentials of -0.3 to -0.4 megapascals. When other plants were allowed to dry to water potentials of -1.2 to -1.7 megapascals, stomatal conductances and CO(2) uptake rates were reduced in magnitude, with the biggest difference in Phase IV photosynthesis. The minor nocturnal response to CO(2) by this species is interpreted to indicate saturated, or nearly saturated, phosphoenolpyruvate carboxylase activity at current atmospheric CO(2) concentrations. CO(2)-enhanced diurnal activity of ribulose bisphosphate carboxylase activity remains a possibility.

Carbon Dioxide Fixation in the Carbon Economy of Developing Seeds of Lupinus albus (L.)

The effects of CO(2) concentration and illumination on net gas exchange and the pathway of (14)CO(2) fixation in detached seeds from developing fruits of Lupinus albus (L.) have been studied.Increasing the CO(2) concentration in the surrounding atmosphere (from 0.03 to 3.0% [v/v] in air) decreased CO(2) efflux by detached seeds either exposed to the light flux equivalent to that transmitted by the pod wall (500 to 600 micro-Einsteins per square meter per second) in full sunlight or held in darkness. Above 1% CO(2) detached seeds made a net gain of CO(2) in the light (up to 0.4 milligrams of CO(2) fixed per gram fresh weight per hour) but (14)CO(2) injected into the gas space of intact fruits (containing around 1.5% CO(2) naturally) was fixed mainly by the pod and little by the seeds.Throughout development seeds contained ribulose-1,5-bisphosphate carboxylase activity (EC 4.1.1.39), especially in the embryo (up to 99 micromoles of CO(2) fixed per gram fresh weight per hour) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) in both testa (up to 280 micromoles of CO(2) fixed per gram fresh weight per hour) and embryo (up to 355 micromoles of CO(2) fixed per gram fresh weight per hour).In kinetic experiments the most significant early formed product of (14)CO(2) fixation in both light and dark was malate but in the light phosphoglyceric acid and sugar phosphates were also rapidly labeled. (14)CO(2) fixation in the light was linked to the synthesis of sugars and amino acids but in the dark labeled sugars were not formed.

Changes in Metabolite Levels in Kalanchoë daigremontiana and the Regulation of Malic Acid Accumulation in Crassulacean Acid Metabolism

Changes in glucose-6-P, fructose-6-P, fructose-1,6-diP, 6-phospho-gluconate, phosphoenolpyruvate, 3-phosphoglycerate, and pyruvate levels in the leaves of the Crassulacean plant Kalanchoë daigremontiana Hammet et Perrier were measured enzymically during transitions from CO(2)-free air to air, air to CO(2)-free air, and throughout the course of acid accumulation in darkness. The data are discussed in terms of the involvement of phosphoenolpyruvate carboxylase in malic acid synthesis and in terms of the regulation of the commencement of malic acid synthesis and accumulation through the effects of CO(2) on storage carbohydrate mobilization and its termination through the effects of malic acid on phosphoenolpyruvate carboxylase activity.

Carbon Dioxide Exchange and Acidity Levels in Detached Pineapple, Ananas comosus (L.), Merr., Leaves during the Day at Various Temperatures, Oxygen and Carbon Dioxide Concentrations

The effects of temperature, O(2), and CO(2) on titratable acid content and on CO(2) exchange were measured in detached pineapple (Ananas comosus) leaves during the daily 15-hour light period. Comparative measurements were made in air and in CO(2)-free air. Increasing the leaf temperature from 20 to 35 C decreased the total CO(2) uptake in air and slightly increased the total CO(2) released into CO(2)-free air. Between 25 and 35 C, the activation energy for daily acid loss was near 12 kcal mol(-1), but at lower temperatures the activation energy was much greater.Increasing O(2) or decreasing the CO(2) concentration decreased the total CO(2) fixation in air, whereas the total CO(2) released in CO(2)-free air was increased. The total acid content remained constant at 20 C, but it decreased progressively with increasing temperature both in air and in CO(2)-free air. The total acid content at 30 C remained constant in 2% O(2) irrespective of CO(2) concentration. The total acid content decreased in 21 and 50% O(2) as the CO(2) increased from 0 to 300, and 540 mul/l of CO(2). The data indicate that photorespiration is present in pineapple. The lack of acid loss in 2% O(2) suggests that light deacidification is dependent upon respiration and that higher O(2) concentrations are required to saturate deacidification.

Effect of carbon dioxide on nitrate accumulation and nitrate reductase induction in corn seedlings

Exposure of the leaf canopy of corn seedlings (Zea mays L.) to atmospheric CO(2) levels ranging from 100 to 800 mul/l decreased nitrate accumulation and nitrate reductase activity. Plants pretreated with CO(2) in the dark and maintained in an atmosphere containing 100 mul/l CO(2) accumulated 7-fold more nitrate and had 2-fold more nitrate reductase activity than plants exposed to 600 mul/l CO(2), after 5 hours of illumination. Induction of nitrate reductase activity in leaves of intact corn seedlings was related to nitrate content. Changes in soluble protein were related to in vitro nitrate reductase activity suggesting that in vitro nitrate reductase activity was a measure of in situ nitrate reduction. In longer experiments, levels of nitrate reductase and accumulation of reduced N supported the concept that less nitrate was being absorbed, translocated, and assimilated when CO(2) was high. Plants exposed to increasing CO(2) levels for 3 to 4 hours in the light had increased concentrations of malate and decreased concentrations of nitrate in the leaf tissue. Malate and nitrate concentrations in the leaf tissue of seven of eight corn genotypes grown under comparable and normal (300 mul/l CO(2)) environments, were negatively correlated. Exposure of roots to increasing concentrations of potassium carbonate with or without potassium sulfate caused a progressive increase in malate concentrations in the roots. When these roots were subsequently transferred to a nitrate medium, the accumulation of nitrate was inversely related to the initial malate concentrations. These data suggest that the concentration of malate in the tissue seem to be related to the accumulation of nitrate.

Photorespiratory phenomena in maize: oxygen uptake, isotope discrimination, and carbon dioxide efflux

Concurrent O(2) evolution, O(2) uptake, and CO(2) uptake by illuminated maize (Zea mays) leaves were measured using (13)CO(2) and (18)O(2). Considerable O(2) uptake occurred during active photosynthesis. At CO(2) compensation, O(2) uptake increased. Associated with this increase was a decrease in O(2) release such that a stoichiometric exchange of O(2) occurred. The rate of O(2) exchange at CO(2) compensation was directly related to O(2) concentration in the atmosphere at least up to 8% (v/v).When illuminated maize leaves were exposed to saturating CO(2) concentrations containing approximately equal amounts of (12)CO(2) and (13)CO(2), the latter was taken up more rapidly, thus depressing the atom% (13)C in the atmosphere. Moreover, upon exposure to CO(2) containing 96 atom% (13)C, there occurred a directly measurable efflux of (12)CO(2) from the leaves for at least 15 minutes. During this period an equimolar evolution of (16)O(2) and uptake of (13)CO(2) was observed. Thereafter, although the rate of (16)O(2) evolution remained unchanged, the rate of (13)CO(2) uptake declined markedly, suggesting continual (13)C enrichment of the photorespiratory substrate.It is concluded that a finite photorespiratory process occurs in maize and that the CO(2) generated thereby is efficiently recycled. Recycling maintains the internal CO(2) concentration at a level difficult to detect by most photorespiratory assays.

Bicarbonate Fixation and Malate Compartmentation in Relation to Salt-induced Stoichiometric Synthesis of Organic Acid

The relationship of malate synthesis to K(+) absorption from solutions of K(2)SO(4) and KHCO(3) was compared in nonvacuolate barley (Hordeum vulgare) root tips and whole excised roots. The comparison has permitted separation of the process which evokes organic acid synthesis from that which leads to stoichiometry between net acid equivalents formed and excess K(+) absorbed from K(2)SO(4), on the one hand, and total K(+) absorbed from KHCO(3), on the other. Both in tips and in roots K(+) uptake from 20 mN salt solution exceeds malate synthesis in the first hour. In vacuolate roots the expected stoichiometry is achieved with time. When root tips are transferred to dilute CaSO(4), malate is rapidly metabolized, and K(+) is lost to the solution. By contrast, in excised whole roots the malate level remains unchanged, the salt-induced organic acid presumably being retained in the vacuole. In excised roots malonate leads to a marked drop in malate levels in untreated roots as well as in roots which have experienced salt-induced net malate synthesis. In consequence, it is contended that malonate makes available normally sequestered vacuolar malate.The general hypothesis is offered that the bicarbonate level of the cytoplasm controls organic acid synthesis by phosphoenolpyruvate carboxylase, and that the cytoplasmic bicarbonate level is raised either by exchange of cytoplasmic H(+) for external cation, or by bicarbonate absorption directly. Stoichiometry, in turn, is achieved by the accumulation in the vacuole of the double salt of malate.

[The influence of low and high oxygen concentrations on oxygen and carbon dioxide gas exchange of Amaranthus and Phaseolus leaves during illumination]

Carbon dioxide and oxygen gas exchange of illuminated Amaranthus and Phaseolus leaves was measured from 0-600 ppm of CO2 in an open system.At low oxygen concentration (2% O2) the ratio of CO2 uptake to O2 evolution came close to 1.At high oxygen partial pressure (42% O2) the O2 compensation point of an Amaranthus leaf was increased and oxygen evolution was depressed. Accordingly the CO2/O2 quotients were variable; the lowest value of 1,9 differed significantly from 1,0.The oxygen and carbon dioxide compensation points of a Phaseolus leaf were increased at high oxygen concentration (42% O2) and oxygen evolution as well as carbon dioxide uptake were reduced. Therefore the ratios CO2 over O2 varied and differed greatly from 1,0.It was concluded that the nature of photosynthates is regulated by the gas composition around the leaves.

Photosynthesis: Temperate and Tropical Characteristics within a Single Grass Genus

Leaves of two subgenera of Panicum differ in photosynthetic physiology and bundle sheath characteristics. Species of the subgenus Eupanicum, like other tropical grasses, had high phosphoenolpyruvate carboxylase (E.C.4.1.1.31) activity, had specialized chloroplasts within the parenchyma bundle sheath cells, and lacked phatorespiration. The pattern for the temperate subgenus Dichanthelium was opposite.

Temperature features of enzymes affecting crassulacean Acid metabolism

Enzymes involved in malic acid production via a pathway with 2 carboxylation reactions and in malic acid conversion via total oxidation have been demonstrated in mitochondria of Bryophyllum tubiflorum Harv. Activation of the mitochondria by Tween 40 was necessary to reveal part of the enzyme activities. The temperature behavior of the enzymes has been investigated, revealing optimal activity of acid-producing enzymes at 35 degrees . Even at 53 degrees the optimum for acid-converting enzymes was not yet reached. From the simultaneous action of acid-producing and acid-converting enzyme systems the overall result at different temperatures was established. Up to 15 degrees the net result was a malic acid production. Moderate temperatures brought about a decrease in this accumulation, which was partly accompanied by a shift to isocitrate production, while at higher temperatures total oxidation of the acids exceeded the production.

Gas exchange of algae. 3. Relation between the concentration of carbon dioxide in the nutrient medium and the oxygen production of Chlorella pyrenoidosa

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.

Physiological Studies on Acid Metabolism in Green Plants. VI. Transaminases in Cell-Free Extracts from Kalanchoë Leaves

Images