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1.
Suspensions of dark-adapted guard cell protoplasts of Vicia faba L. alkalinized their medium in response to irradiation with red light. The alkalinization peaked within about 50 minutes and reached steady state shortly thereafter. Simultaneous measurements of O2 concentrations and medium pH showed that oxygen evolved in parallel with the red light-induced alkalinization. When the protoplasts were returned to darkness, they acidified their medium and consumed oxygen. Both oxygen evolution and medium alkalinization were inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). In photosynthetically competent preparations, light-dependent medium alkalinization is diagnostic for photosynthetic carbon fixation, indicating that guard cell chloroplasts have that capacity. The striking contrast between the responses of guard cell protoplasts to red light, which induces alkalinization, and that to blue light, which activates proton extrusion, suggests that proton pumping and photosynthesis in guard cells are regulated by light quality.  相似文献   

2.
Differences among species in respiration rates in CO2-free air, in light and dark, were studied using the standard leaf chamber technique and the infrared carbon dioxide analyzer. Photosynthesis, transpiration and respiration were measured. In all species studied, rates of respiration were considerably higher in dark than in light. This effect was assumed to be due to reassimilation of the respiratory CO2. A resistance analogy model was derived to account for the apparent differences in internal recycling of CO2 among species; the differences were correlated with differences in maximum photosynthetic rates in normal air and optimal conditions (P310) and with internal resistances to CO2 diffusion (rk). Species with high P310 and low rk appear to reassimilate all the endogenous CO2, whereas other species with lower P310 and higher rk appear to reassimilate only a part of their respiratory CO2. Experiments with the photosynthetic inhibitor, 3-(3,4-dichlorophcnyl)-l,l-dimethyl urea (DCMU), indicated that species with zero respiration in CO2-free air and light release respiratory CO2 when photosynthesis is inhibited. It is concluded that the CO2 released in the presence of DCMU represents respiratory CO2 which recycles to photosynthesis under normal conditions.  相似文献   

3.
In Ankistrodesmus braunii, in the absence of CO2, i.e. in CO2-free air or N2, photosynthetic nitrate uptake and nitrate reduction were inhibited, especially at low pH. Under such conditions, glucose stimulated nitrate uptake and reduction to almost the same level in the pH range between 6 and 8.5. CO2 at 0.03% effected an intermediate pH dependence of nitrate uptake; saturating CO2 concentration (more than 1%) eliminated the pH dependence, as did glucose, but the rates were enhanced compared with glucose. Glucose and, even more, CO2, drastically reduced the release of nitrite and ammonia to the medium, the stoichiometry between alkalinization of the medium and nitrate uptake (OH/NO3) approached 1.  相似文献   

4.
Kelly BM 《Plant physiology》1983,72(2):351-355
Light induced an alkalinization and stimulated a subsequent acidification of the medium surrounding oat (Avena sativa L. cv Garry) leaf protoplasts. Blue light was less effective than would be predicted from photosynthetic action spectra. Nonetheless, 3-(3,4-dichlorophenyl)-1,1-dimethylurea prevented alkalinization and reduced acidification to the dark rate for protoplast suspensions exposed to all light regimes tested.

Alkalinization increased in parallel with initial rates of O2 evolution as the quantum flux density of white light was raised to 75 microeinsteins per square meter per second. Alkalinization was accompanied by a decrease in the CO2 content of the medium; therefore, it was attributed to photosynthetically induced CO2 uptake. The effect of CO2 depletion on the acidity of the medium appeared to be mainly restricted to the first 15 minutes of exposure to light. Consequently, subsequent pH changes primarily reflected a constant net proton efflux. Acidification occurred in the dark, but rates of acidification increased in response to increased light approximately in parallel with changes in a concomitant net O2 efflux. The results indicated that protoplasts could acidify the medium in response to nonphotosynthetic activity, but that photosynthesis mediated light stimulation of acidification.

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5.
Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO2 partial pressure. The K+, Cl? and P contents were then determined by X-ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling. In normal air, the K+ and Cl? contents in guard cells only rose from a light threshold of about 300 μmol m?2 s?1 at which stomata were already largely open. At 600 μmol m?2 s?1, the K+ and Cl? levels in guard cells attained values that were 3- and 8-fold greater, respectively, than the values observed in darkness. The K+ and Cl? contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO2-free air in darkness induced a significant K+ influx towards guard and subsidiary cells. Under light and in CO2-free air, the K+ and Cl? contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO2-free air, the K+ and Cl? contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl?/K+ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K+ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K+ and Cl?, to be practically independent of stomatal aperture.  相似文献   

6.
Blue light (BL) induces stomatal opening through the activation of H+-ATPases with subsequent ion accumulation in guard cells. In most plant species, red light (RL) enhances BL-dependent stomatal opening. This RL effect is attributable to the chloroplasts of guard cell, the only cells in the epidermis possessing this organelle. To clarify the role of chloroplasts in stomatal regulation, we investigated the effects of RL on BL-dependent stomatal opening in isolated epidermis, guard cell protoplasts, and intact leaves of Arabidopsis thaliana. In isolated epidermal tissues and intact leaves, weak BL superimposed on RL enhanced stomatal opening while BL alone was less effective. In guard cell protoplasts, RL enhanced BL-dependent H+-pumping and DCMU, a photosynthetic electron transport inhibitor, eliminated this effect. RL enhanced phosphorylation levels of the H+-ATPase in response to BL, but this RL effect was not suppressed by DCMU. Furthermore, DCMU inhibited both RL-induced and BL-dependent stomatal opening in intact leaves. The photosynthetic rate in leaves correlated positively with BL-dependent stomatal opening in the presence of DCMU. We conclude that guard cell chloroplasts provide ATP and/or reducing equivalents that fuel BL-dependent stomatal opening, and that they indirectly monitor photosynthetic CO2 fixation in mesophyll chloroplasts by absorbing PAR in the epidermis.  相似文献   

7.
Kruse T  Tallman G  Zeiger E 《Plant physiology》1989,91(4):1382-1386
A method for isolating guard cell protoplasts (GCP) from mechanically prepared epidermis of Vicia faba is described. Epidermis was prepared by homogenizing leaves in a Waring blender in a solution of 10% Ficoll, 5 millimolar CaCl2, and 0.1% polyvinylpyrrolidone 40 (PVP). Attached mesophyll and epidermal cells were removed by shaking epidermis in a solution of Cellulysin, mannitol, CaCl2, PVP, and pepstatin A. Cleaned epidermis was transferred to a solution of mannitol, CaCl2, PVP, pepstatin A, cellulase “Onozuka” RS, and pectolyase Y-23 for the isolation of GCP. Preparations made by this method included both adaxial and abaxial GCP and contained ≤0.017% mesophyll protoplasts, ≤0.6% mesophyll fragments, and no epidermal cell contaminants. Yields averaged 9 × 104 protoplasts/leaflet and 98 to 100% of the GCP excluded trypan blue, concentrated neutral red, and hydrolyzed fluorescein diacetate. Isolated GCP increased in diameter by 2.2 micrometers after incubation in darkness in 10 micromolar fusicoccin, 0.4 molar mannitol, 5 millimolar KCl, and 1 millimolar CaCl2. Illumination of GCP with 800 micromoles per square meter per second of red light resulted in alkalinization of their suspension medium. When 10 micromolar per square meter per second of blue light was superimposed onto the red light background, the medium acidified. Measurements of chlorophyll a fast fluorescence transients from isolated GCP indicated that GCP were capable of electron transport, and slow transients contained the “M” peak usually associated with a functional photosynthetic carbon reduction pathway.  相似文献   

8.
The effect of CO2 on potassium transport by Chlorella fusca   总被引:1,自引:1,他引:0  
Abstract. The effect of CO2 on net K+ uptake by Chlorella fusca grown on high CO2 levels was examined by passing 1.5% CO2 through algal suspensions gassed previously with air or CO2-free air Addition of CO2 in the light caused a large net uptake of K+ (initial velocity 4.2–9.2 mmol s?1 m?3 cells) which decreased the concentration of K+ in the supernatant from 0.1–0.2 mol m?3 to 3–10 mmol m?3. In the dark and in the presence of 30 mmol m?3 DCMU, no effects were found. Measurement or the unidirectional K+ fluxes by using 86Rb+ as a label showed that in the presence of 1.5% CO2, influx of K+ was increased by a factor of 2–4 while efflux was inhibited completely. CO2 hyperpolarized the membrane potential (determined through TPP+ uptake) from –120mV to –130 mV which could not explain the more than 15,000-fold K+ accumulations. In the light, CO2 lowered the intracellular pH (determined with DMO) by 0.5 units. In the dark and in the presence of DCMU only, a small acidification of 0.1 units was found. During the first 15 min after addition of CO2 the malate content of the cells increased from 0.7 to 1.5 mol m?3 packed cells. On the basis of these and earlier results, CO2-induced net K+ uptake is interpreted as a stimulation of an electroneutral ATP-dependent K+/H+ exchange at the plasmalemma. This exchange acts as a ‘pHstat’ by reducing the intracellular acidification caused by production of acidic assimilation products.  相似文献   

9.
Mechanically isolated Asparagus sprengeri Regel mesophyll cells cause alkalinization of the suspension medium on the addition of l-glutamate or its analog l-methionine-d,l-sulfoximine. Using a radiolabeled pH probe, it was found that both compounds caused internal acidification whereas l-aspartate did not. Fusicoccin stimulated H+ efflux from the cells by 111% and the uptake of l-[U-14C]glutamate by 55%. Manometric experiments demonstrated that, unlike l-methionine-d,l-sulfoximine, l-glutamate stimulated CO2 evolution from nonilluminated cells. Simultaneous measurements of medium alkalinization and 14CO2 evolution upon the addition of labeled l-glutamate showed that alkalinization was immediate and reached a maximum value after 45 minutes whereas 14CO2 evolution exhibited a lag before its appearance and continued in a linear manner for at least 100 minutes. Rates of alkalinization and uptake of l-[U-14C]glutamate were higher in the light while rates of 14CO2 evolution were higher in the dark. The major labeled product of glutamate decarboxylation, γ-aminobutyric acid, was found in the cells and the suspension medium. Its addition to the cell suspension did not result in medium alkalinization and evidence indicates that it is lost from the cell to the medium. The data suggest that the origin of medium alkalinization is co-transport not metabolism, and that the loss of labeled CO2 and γ-aminobutyric acid from the cell result in an overestimation of the stoichiometry of the H+/l-glutamate uptake process.  相似文献   

10.
The connection between three light responses of green leaf cells-membrane potential (Vm), H+ net efflux and growth, was analyzed. Illumination of mesophyll cells in leaves from Argenteum peas caused two rapid responses: (i) a de- and repolarization of Vm and (ii) an alkalinization of the apoplast. The rapid responses were completely eliminated by the photosynthetic inhibitor 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU) but not affected by ortho-vanadate, an inhibitor of the plasma membrane (PM) H+-ATPase. The rapid changes were followed by a set of delayed responses: (i) a slow, gradual hyperpolarization of Vm, (ii) a gradual acidification of the mesophyll apoplast and (iii) an increased rate of elongation. These three light responses persisted under DCMU but were completely eliminated by vanadate. The data show that the delayed (in contrast to the rapid) responses were due to a stimulation of PM H+ pumps which occurred independently of non-cyclic photosynthetic electron transport and the “dark” processes depending on it. When the rapid responses were blocked by DCMU, light-induced acidification, hyperpolarization of the membrane potential and growth proceeded simultaneously. A shared (4-min) lag phase indicated slower signal processing in mesophyll than in epidermal cells where light stimulation of PM H+ pumps was rapid. Received: 3 September 1998 / Accepted: 15 October 1998  相似文献   

11.
Zelitch I 《Plant physiology》1968,43(11):1829-1837
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO2 in light in a rapid stream of CO2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO2 output in the dark. In maize, photorespiration is only 2% of that in tobacco.

The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-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° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue.

It was concluded that maize does not evolve appreciable quantities of CO2 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 CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities.

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12.
A. Schwartz  E. Zeiger 《Planta》1984,161(2):129-136
The supply of energy for stomatal opening was investigated with epidermal peels of Commelina communis L. and Vicia faba L., under white, blue and red irradiation or in darkness. Fluencerate response curves of stomatal opening under blue and red light were consistent with the operation of two photosystems, one dependent on photosynthetic active radiation (PAR) and the other on blue light, in the guard cells. The PAR-dependent system was 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-sensitive and KCN-resistant and showed a relatively high threshold irradiance for its activation; its activity was most prominent at moderate to high irradiances. The blue-light-dependent photosystem was KCN-sensitive, was active at low irradiances, and interacted with the PAR-dependent photosystem at high blue irradiances. Stomatal opening in darkness, caused by CO2-free air, fusicoccin or high KCl concentrations, was KCN-sensitive and DCMU-resistant. These data indicate that stomatal opening in darkness depends on oxidative phosphorylation for the supply of high-energy equivalents driving proton extrusion. Light-dependent stomatal opening appears to require photophosphorylation from guard-cell chloroplasts and the activation of the blue-light photosystem which could rely either on oxidative phosphorylation or a specific, membrane-bound electron-transport carrier.Abbreviations DCMU 3(3,4-dichlorophenyl)-1-1-dimethylurea - FC fusicoccin - KCN potassium cyanide - PAR photosynthetic active radiation - WL white light  相似文献   

13.
Prelabeled Anabaena variabilis Kütz. evolves 14CO2 in the light with KCN and DCMU (2,4-dichlorophenyl-1,1-dimethylurea) present, comparable to the dark control without inhibitors added. Double-reciprocal plots of CO2 release vs. light intensity with either KCN or KCN+DCMU present result in two straight lines intersecting at the ordinate. Apparently, reducing equivalents originating from carbohydrate catabolism are channeled into the photosynthetic electron-transport chain, competing for electrons from photosystem II. Under these conditions, the CO2 release is accompanied by a light-dependent oxygen uptake, presumably due to oxygen-reducing photosystem-I activity while ribulose-bisphosphate carboxylase is inhibited by KCN.Comparing nine blue-green algae it was shown that only nitrogen-fixing species release substantial amounts of CO2 in the light with KCN or KCN+DCMU present. This release is particularly obvious with Anabaena variabilis Kütz. under nitrogen-fixing conditions, but small when the alga is grown with combined nitrogen.We conclude that nitrogen-fixing species share a common link between respiratory and photosynthetic electron transport. The physiological role may be electron supply of nitrogenase by photosystem I.  相似文献   

14.
Guard cell protoplasts (GCP) were isolated from epidermal stripsof Vicia faba L. by enzymatic digestion. The presence of non-osmoticvolume in the protoplast was suggested by the relationship betweenprotoplast volume and the mannitol concentration of the suspendingmedium. Light illumination caused swelling of GCP only whenKCl was present in the suspending medium. Dark treatment causedshrinking of GCP irrespective of the presence of 10 mM KCl.In the presence of 10 µM abscisic acid (ABA), GCP shrank.Light-induced swelling was suppressed at concentrations of ambientCO2 higher than that in normal air. Promotion of swelling wasnot always observed at lower CO2 concentration. These volumechange responses to light, ABA and CO2 suggest that GCP retainsits physiological activity as a guard cell. The osmotic contributionof K+ to volume increase was lower than expected. Ambient CO2seems to have some effect on the contribution of K+ to osmoregulationof GCP. (Received January 30, 1982; Accepted June 25, 1982)  相似文献   

15.
C. K. Pallaghy 《Planta》1971,101(4):287-295
Summary The correlation between stomatal action and potassium movement in the epidermis of Zea mays was examined in isolated epidermal strips floated on distilled water. Stomatal opening in the isolated epidermis is reversible in response to alternate periods of light or darkness, and is always correlated with a shift in the potassium content of the guard cells. K accumulates in guard cells during stomatal opening, and moves from the guard cells into the subsidiary cells during rapid stomatal closure. When epidermal strips are illuminated in normal air, as against CO2-free air, the stomata do not open and there is a virtually complete depletion of K from the stomatal apparatus. In darkness CO2-containing air inhibits stomatal opening and K accumulation in guard cells, but does not lead to a depletion of K from the stomata as observed in the light.  相似文献   

16.
CO2 exchange rates per unit dry weight, measured in the field on attached fruits of the late-maturing Cal Red peach cultivar, at 1200 μmol photons m?2S?1 and in dark, and photosynthetic rates, calculated by the difference between the rates of CO2 evolution in light and dark, declined over the growing season. Calculated photosynthetic rates per fruit increased over the season with increasing fruit dry matter, but declined in maturing fruits apparently coinciding with the loss of chlorophyll. Slight net fruit photosynthetic rates ranging from 0. 087 ± 0. 06 to 0. 003 ± 0. 05 nmol CO2 (g dry weight)?1 S?1 were measured in midseason under optimal temperature (15 and 20°C) and light (1200 μmol photons m?2 S?1) conditions. Calculated fruit photosynthetic rates per unit dry weight increased with increasing temperatures and photon flux densities during fruit development. Dark respiration rates per unit dry weight doubled within a temperature interval of 10°C; the mean seasonal O10 value was 2. 03 between 20 and 30°C. The highest photosynthetic rates were measured at 35°C throughout the growing season. Since dark respiration rates increased at high temperatures to a greater extent than CO2 exchange rates in light, fruit photosynthesis was apparently stimulated by high internal CO2 concentrations via CO2 refixation. At 15°C, fruit photosynthetic rates tended to be saturated at about 600 μmol photons m?2 S?1. Young peach fruits responded to increasing ambient CO2 concentrations with decreasing net CO2 exchange rates in light, but more mature fruits did not respond to increases in ambient CO2. Fruit CO2 exchange rates in the dark remained fairly constant, apparently uninfluenced by ambient CO2 concentrations during the entire growing season. Calculated fruit photosynthetic rates clearly revealed the difference in CO2 response of young and mature peach fruits. Photosynthetic rates of younger peach fruits apparently approached saturation at 370 μl CO21?2. In CO2 free air, fruit photosynthesis was dependent on CO2 refixation since CO2 uptake by the fruits from the external atmosphere was not possible. The difference in photosynthetic rates between fruits in CO2-free air and 370 μl CO2 1?1 indicated that young peach fruits were apparently able to take up CO2 from the external atmosphere. CO2 uptake by peach fruits contributed between 28 and 16% to the fruit photosynthetic rate early in the season, whereas photosynthesis in maturing fruits was supplied entirely by CO2 refixation.  相似文献   

17.
Fischer RA 《Plant physiology》1968,43(12):1947-1952
This paper reports a consistent and large opening response to light + CO2-free air in living stomata of isolated epidermal strips of Vicia faba. The response was compared to that of non-isolated stomata in leaf discs floating on water; stomatal apertures, guard cell solute potentials and starch contents were similar in the 2 situations. To obtain such stomatal behavior, it was necessary to float epidermal strips on dilute KCl solutions. This suggests that solute uptake is necessary for stomatal opening.

The demonstration of normal stomatal behavior in isolated epidermal strips provides a very useful system in which to investigate the mechanism of stomatal opening. It was possible to show independent responses in stomatal aperture to light and to CO2-free air.

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18.
In M. braunii, the uptake of NO3 and NO2 is blue-light-dependent and is associated with alkalinization of the medium. In unbuffered cell suspensions irradiated with red light under a CO2-free atmosphere, the pH started to rise 10s after the exposure to blue light. When the cellular NO3 and NO2 reductases were active, the pH increased to values of around 10, since the NH4+ generated was released to the medium. When the blue light was switched off, the pH stopped increasing within 60 to 90s and remained unchanged under background red illumination. Titration with H2SO4 of NO3 or NO2 uptake and reduction showed that two protons were consumed for every one NH4+ released. The uptake of Cl was also triggered by blue light with a similar 10 s time response. However, the Cl -dependent alkalinization ceased after about 3 min of blue light irradiation. When the blue light was turned off, the pH immediately (15 to 30 s) started to decline to the pre-adjusted value, indicating that the protons (and presumably the Cl) taken up by the cells were released to the medium. When the cells lacked NO3 and NO2 reductases, the shape of the alkalinization traces in the presence of NO3 and NO2 was similar to that in the presence of Cl, suggesting that NO3 or NO2 was also released to the medium. Both the NO3 and Cl-dependent rates of alkalinization were independent of mono- and divalent cations.  相似文献   

19.
Brix H 《Plant physiology》1968,43(3):389-393
The rate of photorespiration of Douglas-fir seedlings was measured under different light intensities by: (1) extrapolating the curve for CO2 uptake in relation to atmospheric CO2 content to zero CO2 content, and (2) measuring CO2 evolution of the plants into a CO2-free airstream. Different results, obtained from these techniques, were believed to be caused by a severe restriction of the photosynthetic activity when the latter was used. With the first method, CO2 evolution was lower than the dark respiration rate at low light intensity. For all temperatures studied (6°, 20°, 28°) a further increase in light intensity raised the CO2 evolution above dark respiration before it leveled off. The rate of CO2 evolution was stimulated by increase in temperature at all light intensities. With the CO2-free air method, CO2 evolution in the light was less than dark respiration at all light intensities.  相似文献   

20.
The influence of CO2 on the assimilation of nitrate in intact corn seedlings was measured with 15N labelled nitrate, 24 and 48 h after the dark-grown seedlings were transferred to the light, either in normal air or in CO2-free air. During the first 24 h CO2 had no influence on nitrate reduction in intact seedlings. Experiments with detopped seedlings showed that during this period the roots were the only site of nitrate reduction. After 48 h seedlings grown in normal air had reduced more nitrate than detopped seedlings, and seedlings grown in CO2-free air had reduced the same amount of nitrate as detopped seedlings. During the whole 48 h period CO2 had no influence on the level of nitrate reductase of the leaves. It was concluded that in normal air corn leaves started to reduce nitrate after a lag period of 24 h and that in CO2-free air they were incapable of nitrate reduction.  相似文献   

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