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1.
Effects of sulfur on photosynthesis in sugar beets ( Beta vulgaris L. cv. F58-554H1) were studied by inducing sulfur deficiency and determining changes in the photosynthesis of whole attached leaves and of isolated chloroplasts. The rates of photosynthetic CO 2 uptake by intact leaves, photoreduction of ferricyanide, cyclic and noncyclic photophosphorylation of isolated chloroplasts, and the rate of CO 2 assimilation by ribulose diphosphate carboxylase, decreased with decrease in total leaf sulfur from 2500 to about 500 μg g −1 dry weight. Sulfur deficiency reduced photosynthesis through an effect on chlorophyll content, which decreased linearly with leaf sulfur, and by decreasing the rate of photosynthesis per unit chlorophyll. There was only a small effect of sulfur deficiency on stomatal diffusion resistance to CO 2 until leaf sulfur decreased below 1000 μg g −1 when stomatal resistance became a more significant proportion of the total diffusion resistance to CO 2. Light respiration rates were positively correlated with photosynthesis rates and dark respiration was unchanged as leaf sulfur concentrations declined. 相似文献
2.
The ultrastructure of mesophyll chloroplasts of maize ( Zea mays L.) was more severely affected by iron deficiency that induced mild chlorosis than was the ultrastructure of bundle sheath plastids. Ferredoxin and ribulose diphosphate carboxylase levels were severely decreased by iron deficiency. Malic enzyme was less affected, and phosphoenolpyruvate carboxylase activity remained high even under severe iron deficiency. Iron deficient leaves fixed carbon into malic and aspartic acids but the rate of entrance of carbon into the sugar phosphates and sucrose was greatly reduced compared to the control. Chlorophyll a/b ratios ranged from low values of less than 2 in severely iron deficient leaves to high values exceeding 4 in leaves showing little iron deficiency. 相似文献
3.
Photosynthetic CO 2 assimilation, photorespiration and levels of glycollate oxidase and ribulose bisphosphate (RuBP) carboxylase were measured in barley, wheat and maize plants grown on media containing nitrate or ammonium or in plants transferred from nitrate to ammonium. The CO 2 compensation point and photorespiratory CO 2 release were not altered by the nitrogen growth regime nor by transfer from nitrate to ammonium. In barley and wheat plants grown on ammonium the levels of glycollate oxidase and RuBP carboxylase per unit leaf area were higher than in nitrate grown material. These differences were not evident when the results were expressed on a protein or chlorophyll basis. The ratio of glycollate oxidase activity to RuBP carboxylase activity was not altered by the nitrogen regime. 相似文献
4.
Under conditions where glycolate synthesis was inhibited at least 50% in tobacco ( Nicotiana tabacum L.) leaf discs treated with glycidate (2,3-epoxypropionate), the ribulose diphosphate carboxylase activity in extracts and the inhibition of the activity by 100% oxygen were unaffected by the glycidate treatment. [1- 14C]Glycidate was readily taken into leaf discs and was bound to leaf proteins, but the binding occurred preferentially with proteins of molecular weight lower than ribulose diphosphate carboxylase. Glycidate added to the isolated enzyme did not inhibit ribulose diphosphate carboxylase activity or affect its inhibition by 100% O 2. Thus, glycidate did not inhibit glycolate synthesis by a direct effect on ribulose diphosphate carboxylase/oxygenase. 相似文献
5.
Abstract Photosynthetic and anatomical parameters of leaves from the juvenile and adult part of an ivy plant ( Hedera helix L.) have been determined and compared with each other. Light-saturated net photosynthesis (per unit leaf area) was about 1.5 times higher in adult leaves than in juvenile ones. The lower photosynthetic capacity of juvenile leaves was caused by a lower stomatal and especially a lower residual conductance to the CO 2-transfer. This corresponds with anatomical features of the leaves, i.e. lower stomatal frequency, fewer chloroplasts per cell, and – most important – thinner leaves, as well as with a less efficient photosynthetic apparatus measured as Hill reaction of isolated broken chloroplasts and activity of ribulose bisphosphate carboxylase. No differences in the respiration in light (relative to net photosynthesis) and in the CO 2-compensation concentration could be detected between the two leaf types. These observed anatomical and photosynthetic parameters of the juvenile and adult ivy leaves resemble those reported for shade and sun leaves, respectively, although the leaves investigated originated from the same light environment. 相似文献
6.
A high-affinity form of ribulose diphosphate carboxylase, observed transiently in spinach-leaf extracts soon after extraction, was inhibited by O 2 competitively with respect to CO 2. Analogously, the ribulose diphosphate oxygenase activity for this form was inhibited by CO 2, competitively with respect to O 2. For each gas, the K m for the reaction in which it was a substrate was similar to its K i for the reaction it inhibited. The Arrhenius activation energy for the oxygenase reaction was 1.5 times that of the carboxylase. These characteristics are consistent with ribulose diphosphate oxygenase being the enzymatic reaction responsible for synthesizing the substrate for photorespiration and with the concept that the balance between photosynthesis and photorespiration of leaves is a reflection of the ratio between the two activities of this bi-functional enzyme. 相似文献
7.
Photosynthetic carbon assimilation in plants is regulated by activity of the ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase. Although the carboxylase requires CO 2 to activate the enzyme, changes in CO 2 between 100 and 1,400 microliters per liter did not cause changes in activation of the leaf carboxylase in light. With these CO 2 levels and 21% O 2 or 1% or less O 2, the levels of ribulose bisphosphate were high and not limiting for CO 2 fixation. With high leaf ribulose bisphosphate, the Kact(CO 2) of the carboxylase must be lower than in dark, where RuBP is quite low in leaves. When leaves were illuminated in the absence of CO 2 and O 2, activation of the carboxylase dropped to zero while RuBP levels approached the binding site concentration of the carboxylase, probably by forming the inactive enzyme-RuBP complex. The mechanism for changing activation of the RuBP carboxylase in the light involves not only Mg2+ and pH changes in the chloroplast stroma, but also the effects of binding RuBP to the enzyme. In light when RuBP is greater than the binding site concentration of the carboxylase, Mg2+ and pH most likely determine the ratio of inactive enzyme-RuBP to active enzyme-CO2-Mg2+-RuBP forms. Higher irradiances favor more optimal Mg2+ and pH, with greater activation of the carboxylase and increased photosynthesis. 相似文献
8.
Because glyoxylate inhibits CO 2 fixation by intact chloroplasts and purified ribulose bisphosphate carboxylase/oxygenase, glyoxylate might be expected to exert some regulatory effect on photosynthesis. However, ribulose bisphosphate carboxylase activity and activation in intact chloroplasts from Spinacia oleracea L. leaves were not substantially inhibited by 10 millimolar glyoxylate. In the light, the ribulose bisphosphate pool decreased to half when 10 millimolar glyoxylate was present, whereas this pool doubled in the control. When 10 millimolar glyoxylate or formate was present during photosynthesis, the fructose bisphosphate pool in the chloroplasts doubled. Thus, glyoxylate appeared to inhibit the regeneration of ribulose bisphosphate, but not its utilization. The fixation of CO2 by intact chloroplasts was inhibited by salts of several weak acids, and the inhibition was more severe at pH 6.0 than at pH 8.0. At pH 6.0, glyoxylate inhibited CO2 fixation by 50% at 50 micromolar, and glycolate caused 50% inhibition at 150 micromolar. This inhibition of CO2 fixation seems to be a general effect of salts of weak acids. Radioactive glyoxylate was reduced to glycolate by chloroplasts more rapidly in the light than in the dark. Glyoxylate reductase (NADP+) from intact chloroplast preparations had an apparent Km (glyoxylate) of 140 micromolar and a Vmax of 3 micromoles per minute per milligram chlorophyll. 相似文献
9.
Phosphorus-deficient spinach plants were grown by transferring them to nutrient solutions without PO 4. Photosynthetic rates were measured at a range of intercellular CO 2 partial pressures from 50–500 bar and then the leaves were freeze-clamped in situ to measure ribulose bisphosphate carboxylase (Rubisco) activity and metabolite concentrations. Compared with control leaves, deficient leaves had significantly lower photosynthetic rates, percentage activation of Rubisco, and amounts of ribulose bisphosphate and 3-phosphoglycerate at all CO 2 partial pressures. After feeding 10 mM PO 4 to the petioles of detached deficient leaves, all these measurements increased within 2 hours. At atmospheric CO 2 partial pressure the photosynthetic rate was stimulated in 19 mbar O 2 compared with 200 mbar. At higher CO 2 partial pressures this stimulation was less but the percentage stimulation in deficient leaves was no different from controls in either CO 2 partial pressure. It was concluded that phosphorus deficiency affects both Rubisco activity and the capacity for ribulose bisphosphate regeneration, and possible causes are discussed.Abbreviations A
CO 2 assimilation rate
- C i
intercellular CO 2 partial pressure
- PGA
3-phosphoglycerate
- RuP 2
ribulose 1,5-bisphosphate
- Rubisco
RuP 2 carboxylase/oxygenase 相似文献
10.
Kinetic properties of soybean net photosynthetic CO 2 fixation and of the carboxylase and oxygenase activities of purified soybean ( Glycine max [L.] Merr.) ribulose 1, 5-diphosphate carboxylase (EC 4.1.1.39) were examined as functions of temperature, CO 2 concentration, and O 2 concentration. With leaves, O 2 inhibition of net photosynthetic CO 2 fixation increased when the ambient leaf temperature was increased. The increased inhibition of CO 2 fixation at higher temperatures was caused by a reduced affinity of the leaf for CO 2 and an increased affinity of the leaf for O 2. With purified ribulose 1,5-diphosphate carboxylase, O 2 inhibition of CO 2 incorporation and the ratio of oxygenase activity to carboxylase activity increased with increased temperature. The increased O 2 sensitivity of the enzyme at higher temperature was caused by a reduced affinity of the enzyme for CO 2 and a slightly increased affinity of the enzyme for O 2. The similarity of the effect of temperature on the affinity of intact leaves and of ribulose 1,5-diphosphate carboxylase for CO 2 and O 2 provides further evidence that the carboxylase regulates the O 2 response of photosynthetic CO 2 fixation in soybean leaves. Based on results reported here and in the literature, a scheme outlining the stoichiometry between CO 2 and O 2 fixation in vivo is proposed. 相似文献
11.
Ribulose 1,5-bisphosphate in the chloroplast has been suggested to regulate the activity of the ribulose bisphosphate carboxylase/oxygenase. To generate high levels of ribulose bisphosphate, isolated and intact spinach chloroplasts were illuminated in the absence of CO 2. Under these conditions, chloroplasts generate internally up to 300 nanomoles ribulose 1,5-bisphosphate per milligram chlorophyll if O 2 is also absent. This is equivalent to 12 millimolar ribulose bisphosphate, while the enzyme, ribulose bisphosphate carboxylase, offers up to 3.0 millimolar binding sites for the bisphosphate in the chloroplast stroma. During illumination, the ribulose bisphosphate carboxylase is deactivated, due mostly to the absence of CO 2 required for activation. The rate of deactivation of the ribulose bisphosphate carboxylase was not affected by the chloroplast ribulose bisphosphate levels. Upon addition of CO 2, the carboxylase in the chloroplast was completely reactivated. Of interest, addition of 3-phosphoglycerate stopped deactivation of the carboxylase in the chloroplast while ribulose bisphosphate accumulated. With intact chloroplasts in light, no correlation between deactivation of the carboxylase and ribulose bisphosphate levels could be shown. 相似文献
12.
d-Ribulose 1,5-diphosphate carboxylase from extracts of the unicellular blue-green alga Aphanocapsa 6308 has been purified by ammonium sulphate precipitation and linear sucrose density gradient centrifugation. The molecular weight was estimated to be 525 000 and the enzyme consisted of two types of sub-unit of molecular weights 51 000 and 15 000. The small sub-units were not detected after purification involving acid precipitation but were observed if the acid precipitation step was omitted. The Michaelis constants for Mg 2+ and CO 2, when tested under air, were 0.35 mM and 0.071 mM respectively. Oxygen acted as a competitive inhibitor with respect to CO 2, suggesting that the enzyme also acts as an oxygenase. This was confirmed by measuring ribulose diphosphate-dependent O 2 uptake. A 1:1 stoichiometry between ribulose diphosphate utilization and O 2 consumption was observed. 6-Phosphogluconate inhibited carboxylase activity both at high (20 mM) and low (1 mM) bicarbonate concentrations. The data are compared with the properties of ribulose diphosphate carboxylase from other autotrophic prokaryotes and from chloroplasts.Abbreviations RuDP
d-Ribulose 1,5-diphosphate
- EDTA
ethylene diamine tetraacetic acid
- GSH
reduced glutathione
- SDS
sodium dodecyl sulphate
- 6PGluc
6-phosphogluconate
- STB
supplemented Tris buffer 相似文献
13.
Bicarbonate uptake by isolated chloroplast envelope membranes and intact chloroplasts of spinach ( Spinacia oleracea L. var. Viroflay) in darkness exhibited a similar dependency upon temperature, pH, time, and concentrations of isolated or attached envelope membranes. This similarity in uptake properties demonstrates the usefulness of the envelope membranes for the study of chloroplast permeability. Maximal rates for dark HCO 3- uptake by isolated envelope membranes and intact chloroplasts were more than sufficient to account for the maximal rates of photosynthetic CO 2 fixation observed with intact chloroplasts. The active species involved in the uptake process was found to be HCO 3- and not CO 2. The significance of HCO 3- uptake and its relationship to carbonic anhydrase and ribulose diphosphate carboxylase is discussed. Conditions for maximal HCO 3- uptake in darkness by intact chloroplasts were found to be similar to those required for maximal photosynthetic CO 2 fixation, suggesting that HCO 3- uptake by the envelope membrane may regulate photosynthetic CO 2 fixation. 相似文献
14.
Increasing photosynthetic photon flux density (PPFD) received during development from 5.5 to 31.2 mol m -2 d -1 resulted in greater leaf and mesophyll cell surface areas in cotton ( Gossypium hirsutum L.). The relationships between the amounts of these surface areas and potential CO 2 assimilation by these leaves were evaluated. Leaf area (epidermal surface area of one side of a leaf), mesophyll cell surface area, and net rate of CO 2 uptake (P n) were measured from the time leaves first unfolded until P., was substantially reduced. At the higher PPFD, leaf and mesophyll surface areas increased more rapidly during expansion, and P n per unit leaf area was greater than at the lower PPFD. Although leaves at the higher PPFD reached the maximum P., per unit mesophyll cell surface area 4 to 5 days earlier than leaves at the lower PPFD, the maxima for these P., were similar. Leaves grown at the higher PPFD had the potential to assimilate 2.2, 3.5, or 5.8 times the amount of CO 2 as leaves from the lower PPFD when P., was expressed per unit mesophyll surface, per unit leaf surface, or per whole leaf, respectively. Greater and earlier development of both P., and mesophyll cell surface area at higher PPFD apparently had a compounding effect on the potential for carbon assimilation by a leaf. 相似文献
15.
Effects of salinity and nutrients on carbon gain in relation to water use were studied in the grey mangrove, Avicennia marina, growing along a natural salinity gradient in south‐eastern Australia. Tall trees characterized areas of seawater salinities (fringe zone) and stunted trees dominated landward hypersaline areas (scrub zone). Trees were fertilized with nitrogen (+N) or phosphorus (+P) or unfertilized. There was no significant effect of +P on shoot growth, whereas +N enhanced canopy development, particularly in scrub trees. Scrub trees maintained greater CO 2 assimilation per unit water transpired (water‐use efficiency, WUE) and had lower nitrogen‐use efficiency (NUE; CO 2 assimilation rate per unit leaf nitrogen) than fringe trees. The CO 2 assimilation rates of +N trees were similar to those in other treatments, but were achieved at lower transpiration rates, stomatal conductance and intercellular CO 2 concentrations. Maintaining comparable assimilation rates at lower stomatal conductance requires greater ribulose 1·5‐bisphosphate carboxylase/oxygenase activity, consistent with greater N content per unit leaf area in +N trees. Hence, +N enhanced WUE at the expense of NUE. Instantaneous WUE estimates were supported by less negative foliar δ13C values for +N trees and scrub control trees. Thus, nutrient enrichment may alter the structure and function of mangrove forests along salinity gradients. 相似文献
16.
Light and dark 14CO 2 assimilation, pulse-chase ( 14CO 2 followed by 12CO 2) labeling experiments both in the light and in the dark, photorespiratory activity and some enzymes (ribulose 1,5-bisphosphate (RuBP) carboxylase, phosphoenolpyruvate (PEP) carboxylase, and NADP-malic enzyme) were followed in sections of 2.5 centimeters from the base (younger tissue) to the tip (oldest tissue) of the green maize leaf. Tissue was taken from the third leaf of 12- to 16-day-old plants consisting of sections 0 to 2.5 centimeters (base), 4.5 to 7.0 centimeters (center) and 9.0 to 11.5 centimeters (top) measured from the base. Some of these properties were also determined in the intact leaves of 4-day-old maize plants. 相似文献
17.
Ribulose diphosphate carboxylase was found to exist in two distinct kinetic forms in spinach leaf extracts. One form displayed an apparent Km for CO 2 in excess of 200 μm and is likely to be the form purified and studied by many previous workers. However, if leaf extracts were prepared in the presence of Mg 2+ and atmospheric levels of CO 2, the recently described high-affinity form was obtained. It had a Km for CO 2 of about 20 μm, was quite stable even at 25 °C, and its properties were consistent with it being the form which operates in photosynthesis in vivo. Mg 2+ was also able to convert the high- Km (CO 2) form to the low- Km (CO 2) form when it was added to an extract which had been prepared in its absence. Mg 2+ was more effective in causing this conversion if bicarbonate was added as well. This activating effect of bicarbonate is a probable cause of previously reported apparent homotropic effects of bicarbonate on ribulose diphosphate carboxylase activity. It is possible that the apparently high- Km (CO 2) form is not intrinsically active and appears to have activity only by virtue of the low- Km (CO 2) form produced by contact with Mg 2+ and bicarbonate (or CO 2) during the course of the assay. Extracts prepared with ribose 5-phosphate in the absence of Mg 2+ also showed low- Km (CO 2) carboxylase activity initially, but the presence of this sugar phosphate was deleterious during storage at 25 °C, where it promoted conversion to the apparently high- Km (CO 2) form.Effects on the affinity of ribulose diphosphate carboxylase for CO 2 were paralleled by effects on the activity of the associated ribulose diphosphate oxygenase. Treatments which produced the low- Km (CO 2) form of the carboxylase also resulted in high oxygenase activity, and it is possible that the apparently high- Km (CO 2) form of the carboxylase has little, if any, oxygenase activity associated with it.The carboxylase and oxygenase activities of the low- Km (CO 2) form showed broad and quite similar responses to pH variation, and the oxygenase had a Km for O 2 of 0.22 mm.The stability of the low- Km (CO 2) form in the presence of Mg 2+ and bicarbonate was quite sufficient for it to be partially purified by Sepharose chromatography. The significance of the low- Km (CO 2) form is discussed with respect to activation of photosynthesis by Mg 2+. 相似文献
18.
Special culture conditions for Euglena gracilis Z and ZR are described. They induce interactions between the chloroplast and mitochondrial metabolisms leading to paramylon synthesis. When grown in continuous light under pure nitrogen and in the presence of lactate as the sole carbon source, sugar synthesis occurs during the first 24 h of culture with the participation of both mitochondria (using lactate) and of chloroplasts (fixing CO 2 from lactate decarboxylation). The activities of ribulose bisphosphate carboxylase, phosphoenolpyruvate carboxylase, and phosphoenolpyruvate carboxykinase are very high and mitochondria and chloroplasts develop then a common network of vesicles in which paramylon grains can be seen. Electron micrographs demonstrate membrane continuity between the two types of organelles. Occasionally the mitochondrial matrix and the chloroplast stroma are separated by only a unit membrane.Abbreviations Chl
chlorophyll
- OAA
oxaloacetic acid
- PEP
phosphoenolpyruvate
- RuBP
ribulose bisphosphate
- DTT
1,4-dithiothreitol
- PVP
polyvinylpyrrolidone 相似文献
19.
The pathway of carbon assimilation in greening roots was compared to the pathway in leaves of Lens culinaris seedlings by means of labelling distribution analysis among the products of 14CO 2 fixation in vivo, and in vitro with ribulose 1,5-diphosphate as the substrate. In green leaves, CO 2 fixation via ribulose 1,5-diphosphate carboxylase predominated largely while, in green roots, this carboxylase activity and the phosphoenolpyruvate carboxylase contributed almost equally to the whole in vivo CO 2 fixation. A participation of the activities of both carboxylases according to the double carboxylation pathway in the synthesis of dicarboxylic acids (malate and aspartate) was demonstrated in vitro after 48 h of greening in roots but seemed to be absent in in vivo experiments. 相似文献
20.
Summary Sugar cane chloroplasts isolated in simple media possessed little photochemical activity, but showed rapid O 2 uptake, independent of light. A similar rapid consumption of O 2 was observed with brei prepared from cane leaves. This was not observed in brei of spinach leaves. Authentic polyphenols and cane leaf extracts stimulated the consumption of O 2 by cane preparations and inhibited photosynthesis in chloroplasts isolated from spinach. Chlorogenic acid and caffeic acid were the major o-diphenols in extracts of cane leaves. These compounds inhibited reactions associated with CO 2 fixation by the photosynthetic carbon reduction cycle. Assimilation of CO 2 due to phosphoenol pyruvate carboxylase activity was less sensitive to inhibition by o-diphenols. Mechanisms are discussed whereby o-diphenols may inhibit cane chloroplasts during their isolation. 相似文献
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