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PubMed1998

Does leaf position within a canopy affect acclimation of photosynthesis to elevated CO2?. Analysis Of a wheat crop under free-air co2 enrichment

Previous studies of photosynthetic acclimation to elevated CO2 have focused on the most recently expanded, sunlit leaves in the canopy. We examined acclimation in a vertical profile of leaves through a canopy of wheat (Triticum aestivum L.). The crop was grown at an elevated CO2 partial pressure of 55 Pa within a replicated field experiment using free-air CO2 enrichment. Gas exchange was used to estimate in vivo carboxylation capacity and the maximum rate of ribulose-1,5-bisphosphate-limited photosynthesis. Net photosynthetic CO2 uptake was measured for leaves in situ within the canopy. Leaf contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), light-harvesting-complex (LHC) proteins, and total N were determined. Elevated CO2 did not affect carboxylation capacity in the most recently expanded leaves but led to a decrease in lower, shaded leaves during grain development. Despite this acclimation, in situ photosynthetic CO2 uptake remained higher under elevated CO2. Acclimation at elevated CO2 was accompanied by decreases in both Rubisco and total leaf N contents and an increase in LHC content. Elevated CO2 led to a larger increase in LHC/Rubisco in lower canopy leaves than in the uppermost leaf. Acclimation of leaf photosynthesis to elevated CO2 therefore depended on both vertical position within the canopy and the developmental stage.

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PubMed1998

Evolution of C4 photosynthesis in flaveria species. Isoforms Of nadp-malic enzyme

NADP-malic enzyme (NADP-ME, EC 1.1.1.40), a key enzyme in C4 photosynthesis, provides CO2 to the bundle-sheath chloroplasts, where it is fixed by ribulose-1,5-bisphosphate carboxylase/oxygenase. We characterized the isoform pattern of NADP-ME in different photosynthetic species of Flaveria (C3, C3-C4 intermediate, C4-like, C4) based on sucrose density gradient centrifugation and isoelectric focusing of the native protein, western-blot analysis of the denatured protein, and in situ immunolocalization with antibody against the 62-kD C4 isoform of maize. A 72-kD isoform, present to varying degrees in all species examined, is predominant in leaves of C3 Flaveria spp. and is also present in stem and root tissue. By immunolabeling, NADP-ME was found to be mostly localized in the upper palisade mesophyll chloroplasts of C3 photosynthetic tissue. Two other isoforms of the enzyme, with molecular masses of 62 and 64 kD, occur in leaves of certain intermediates having C4 cycle activity. The 62-kD isoform, which is the predominant highly active form in the C4 species, is localized in bundle-sheath chloroplasts. Among Flaveria spp. there is a 72-kD constitutive form, a 64-kD form that may have appeared during evolution of C4 metabolism, and a 62-kD form that is necessary for the complete functioning of C4 photosynthesis.

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PubMed1998

Does a low nitrogen supply necessarily lead to acclimation of photosynthesis to elevated CO2?

Long-term exposure of plants to elevated partial pressures of CO2 (pCO2) often depresses photosynthetic capacity. The mechanistic basis for this photosynthetic acclimation may involve accumulation of carbohydrate and may be promoted by nutrient limitation. However, our current knowledge is inadequate for making reliable predictions concerning the onset and extent of acclimation. Many studies have sought to investigate the effects of N supply but the methodologies used generally do not allow separation of the direct effects of limited N availability from those caused by a N dilution effect due to accelerated growth at elevated pCO2. To dissociate these interactions, wheat (Triticum aestivum L.) was grown hydroponically and N was added in direct proportion to plant growth. Photosynthesis did not acclimate to elevated pCO2 even when growth was restricted by a low-N relative addition rate. Ribulose-1, 5-bisphosphate carboxylase/oxygenase activity and quantity were maintained, there was no evidence for triose phosphate limitation of photosynthesis, and tissue N content remained within the range recorded for healthy wheat plants. In contrast, wheat grown in sand culture with N supplied at a fixed concentration suffered photosynthetic acclimation at elevated pCO2 in a low-N treatment. This was accompanied by a significant reduction in the quantity of active ribulose-1, 5-bisphosphate carboxylase/oxygenase and leaf N content.

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PubMed1999

The relationship between photosynthesis and a mastoparan-induced hypersensitive response in isolated mesophyll cells

The G-protein activator mastoparan (MP) was found to elicit the hypersensitive response (HR) in isolated Asparagus sprengeri mesophyll cells at micromolar concentrations. The HR was characterized by cell death, extracellular alkalinization, and an oxidative burst, indicated by the reduction of molecular O2 to O2. To our knowledge, this study was the first to monitor photosynthesis during the HR. MP had rapid and dramatic effects on photosynthetic electron transport and excitation energy transfer as determined by variable chlorophyll a fluorescence measurements. A large increase in nonphotochemical quenching of chlorophyll a fluorescence accompanied the initial stages of the oxidative burst. The minimal level of fluorescence was also quenched, which suggests the origin of this nonphotochemical quenching to be a decrease in the antenna size of photosystem II. In contrast, photochemical quenching of fluorescence decreased dramatically during the latter stages of the oxidative burst, indicating a somewhat slower inhibition of photosystem II electron transport. The net consumption of O2 and the initial rate of O2 uptake, elicited by MP, were higher in the light than in the dark. These data indicate that light enhances the oxidative burst and suggest a complex relationship between photosynthesis and the HR.

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PubMed1999

Photosynthesis and carbon partitioning in transgenic tobacco plants deficient in leaf cytosolic pyruvate kinase

Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco (Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PKc-). PKc- plants cultivated under a low light intensity (100 &mgr;mol m-2 s-1) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PKc (PKc+). PKc- and PKc+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed 14CO2 during photosynthesis. However, during growth under low light the nighttime, export of previously fixed 14CO2 by fully expanded PKc- leaves was 40% lower, whereas concurrent respiratory 14CO2 evolution was 40% higher than that of PKc+ leaves. This provides a rationale for the reduced root growth of the PKc- plants grown at low irradiance. Leaf photosynthetic and export characteristics in PKc- and PKc+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PKc in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low.

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PubMed1999

Analysis of the relative increase in photosynthetic O(2) uptake when photosynthesis in grapevine leaves is inhibited following low night temperatures and/or water stress

We found similarities between the effects of low night temperatures (5 degrees C-10 degrees C) and slowly imposed water stress on photosynthesis in grapevine (Vitis vinifera L.) leaves. Exposure of plants growing outdoors to successive chilling nights caused light- and CO(2)-saturated photosynthetic O(2) evolution to decline to zero within 5 d. Plants recovered after four warm nights. These photosynthetic responses were confirmed in potted plants, even when roots were heated. The inhibitory effects of chilling were greater after a period of illumination, probably because transpiration induced higher water deficit. Stomatal closure only accounted for part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O(2) evolution, even at high external CO(2) concentrations. Oxygen isotope exchange revealed that this imbalance was due to increased O(2) uptake, which probably has two components: photorespiration and the Mehler reaction. Chilling- and drought-induced water stress enhanced both O(2) uptake processes, and both processes maintained relatively high rates of electron flow as CO(2) exchange approached zero in stressed leaves. Presumably, high electron transport associated with O(2) uptake processes also maintained a high DeltapH, thus affording photoprotection.

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PubMed1966

Rate of Glycolate Formation During Photosynthesis at High pH.

The products of C(14)O(2) fixation by Chlamydomonas and Chlorella were studied under conditions most favorable for glycolate synthesis. The highest percentage of the C(14) was incorporated into glycolate in the pH range of 8 to 9. After 1 to 2 minutes as much as 40% of the C(14) was found in glycolate products and only a trace of C(14) was present as phosphoglycerate. Below pH 8 the rate of photosynthesis was much faster, but only a small percent of the C(14) was incorporated into glycolate in 1 or 2 minutes, while a high percent of the C(14) accumulated in phosphoglycerate. C(14) labeling of glycolate even at pH 8 or above did not occur at times shorter than 10 seconds. During the first seconds of photosynthesis, nearly all of the C(14) was found in phosphoglycerate and sugar phosphates. Thus glycolate appears to be formed after the phosphate esters of the photosynthetic carbon cycle.Washing Chlamydomonas with water 2 or 3 times resulted in the loss of most of their free phosphate. When a small aliquot of NaHC(14)O(3) was added to washed algae in the absence of this buffering capacity, the pH of the algal medium became 8 or above and much of the fixed C(14) accumulated in glycolate.

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PubMed1966

Effect of oxygen on photosynthesis, photorespiration and respiration in detached leaves. I. Soybean.

The effect of O(2) on the CO(2) exchange of detached soybean leaves was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems.The rate of apparent photosynthesis was inhibited by O(2) while the steady rate of respiration after a few minutes in the dark was not affected. Part of the inhibition of apparent photosynthesis was shown to be a result of increased photorespiration. This stimulation of photorespiration by O(2) was manifested by an increase in the CO(2) compensation point.The differential effects of O(2) on dark respiration (no effect) and photorespiration (stimulation) indicated that these were 2 different processes.Moreover the extrapolation of the CO(2) compensation point to zero at zero O(2) indicated that dark respiration was suppressed in the light at least at zero O(2) concentration.

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PubMed1966

Effect of Oxygen on Photosynthesis, Photorespiration and Respiration in Detached Leaves. II. Corn and other Monocotyledons.

The effect of O(2) on the CO(2) exchange of detached leaves of corn (Zea mays), wheat (Triticum vulgare), oats (Avena sativa), barley (Hordeum vulgare), timothy (Phleum pratense) and cat-tail (Typha angustifolia) was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems.Corn leaves did not produce CO(2) in the light at any O(2) concentration, as was shown by the zero CO(2) compensation point and the absence of a CO(2) burst in the first minute of darkness. The rate of photosynthesis was inhibited by O(2) and the inhibition was not completely reversible. On the other hand, the steady rate of respiration after a few minutes in the dark was not affected by O(2).These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O(2) in the same way.The other 5 monocotyledons studied did produce CO(2) in the light. Moreover, the CO(2) compensation point increased linearly with O(2) indicating a stimulation of photorespiration.The implications of the lack of photorespiration in studies of primary productivity are discussed.

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PubMed1966

Glycolic Acid Labeling During Photosynthesis with CO(2) and Tritiated Water.

Chlorella pyrenoidosa were allowed to photosynthesize for short periods of time in the presence of (14)CO(2) and HTO. Analysis of tritium and (14)C labeling of photosynthetic intermediate compounds showed that the T/(14)C ratio of glycolic acid was comparable to that of intermediate compounds of the photosynthetic carbon reduction cycle when photosynthesis was performed in nearly 100% oxygen and only slightly higher under steady-state conditions. It is concluded that formation of labeled glycolic acid as a consequence of its proposed hydrogen transport role in photosynthesis is quantitatively of limited importance compared to the net synthesis of glycolic acid from CO(2).

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PubMed1968

The effects of ultraviolet irradiation on a coccoid blue-green alga: survival, photosynthesis, and photoreactivation.

The effects of UV irradiation (254 mmu) 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 mmu. 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.

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PubMed1968

Inhibition of the formation of photosynthetic enzymes by inhibitors of photosynthesis.

It has been shown previously that an increase in ribulose diphosphate carboxylase activity occurs upon brief illumination of leaves of dark-grown Zea mays plants; an increase in ribose 5-phosphate isomerase occurs after prolonged illumination. Both of these responses to illumination are inhibited by chloramphenicol.The administration of p-chlorophenyldimethylurea, an inhibitor of photosynthesis, to etiolated maize does not affect the normal early rise in ribulose diphosphate carboxylase activity when the leaves are illuminated but does block the increase in ribose 5-phosphate isomerase. This pattern of response suggests that photosynthetic activity is required for the increase in isomerase-perhaps products of photosynthesis induce isomerase synthesis-but that the level of ribulose diphosphate carboxylase is controlled by other processes. Chlorophyll formation (as has been shown by others) is slightly suppressed by the inhibitor; levels of total soluble leaf protein appear to be unaffected.Salicylaldoxime, which is a more general inhibitor of metabolism than p-chlorophenyldimethylurea, arrests the normally observed increases of ribulose diphosphate carboxylase, ribose 5-phosphate isomerase, and chlorophyll during illumination of dark-grown maize. The level of soluble leaf protein is also lower in leaves treated with this compound.

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PubMed1969

Relation of CO(2) Compensation Concentration to Apparent Photosynthesis in Maize.

Significant differences in CO(2) compensation concentration measured in the field among varieties of the species Zea mays L. are reported for the first time. CO(2) compensation concentrations were significantly (P</= 0.01) and negatively correlated with apparent photosynthesis at 300 mul CO(2)/liter air. The Michaelis constant (as defined) for a leaf was significantly (P</= 0.01) and positively correlated with apparent photosynthesis among varieties. While the first correlation is similar to behavior of CO(2) compensation among species of different photosynthetic efficiency, the latter correlation is the converse of the behavior of Km among species.

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PubMed1969

Effects of Temperature on Photosynthesis and CO(2) Evolution in Light and Darkness by Green Leaves.

Using an open and a closed system of gas analysis, it was found that CO(2) evolution in light and in darkness from plant leaves (sunflower, soybean, watermelon, eggplant, and jackbean) have a different response to temperature. While the rate of CO(2) evolution in light increased with increasing temperature from 17 to 35 degrees and then declined, the rate of CO(2) evolution in darkness increased continuously up to 40 degrees . The rate of CO(2) evolution in light was affected by light intensity. At 1800 ft-c and below 35 degrees the rate of CO(2) evolution in light was greater than in darkness, but above 35 degrees it became lower than in darkness. The Q(10) for CO(2) evolution in light was consistently lower than that in darkness.Apparent photosynthesis decreased with increasing temperature, from 20 to 40 degrees and its rate was affected by both light intensity and oxygen concentration. In leaves of dicotyledonous plants studied the decrease in apparent photosynthesis between 20 to 30 degrees at 21% O(2) was shown to be due primarily to an increase in CO(2) evolution in light with relatively little effect on photosynthesis.In corn which does not evolve CO(2) during illumination there was little effect of increasing temperature on the rate of apparent photosynthesis.The different response to temperature of CO(2) evolution in light and in darkness support the earlier conclusion that these are 2 different processes.

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PubMed1969

Carbon Dioxide Exchanges in Leaves. I. Discrimination Between CO(2) and CO(2) in Photosynthesis.

In order to measure CO(2) exchange reactions by leaves using isotopes of CO(2), it is necessary to know precisely the discrimination against (14)CO(2) by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO(2) in light, and so provide suitable material for this measurement. Discrimination against (14)CO(2) in photosynthesis by maize leaves is almost precisely the same as in CO(2) absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of (12)CO(2) and (14)CO(2), calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against (14)CO(2) in photosynthesis.

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PubMed1971

The Effect of pH on the Products of Photosynthesis in CO(2) by Chloroplast Preparations from Acetabularia mediterranea.

The effect of pH on the pathways of carbon in photosynthesis was examined in chloroplast preparations from Acetabularia mediterranea. The flow of carbon into a number of photosynthetic intermediates, particularly sucrose, glycine, serine, glycolate, and the insoluble fraction, was strongly influenced by pH. At higher pH a much larger portion of the (14)C entered intermediates of the glycolate pathway. Although maximal apparent photosynthesis occurred at pH 7.6 to 7.7, cytoplasmic pH was found to be 8.0 to 8.4, using indicators. The pattern of distribution of (14)C in intermediates of whole cells was closest to that in chloroplasts at the higher pH range.

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PubMed1972

Antimycin A Stimulation of Rate-limiting Steps of Photosynthesis in Isolated Spinach Chloroplasts.

Changes in levels of metabolites in isolated spinach (Spinacia oleracea) chloroplasts seen upon addition of antimycin A suggest that the activities of enzymes mediating several regulated reactions are affected. Apparently, the presence of added antimycin A does not increase the level of CO(2) in the chloroplasts, nor does it stimulate CO(2) fixation by increasing the level of the carboxylation substrate, ribulose-1,5-diphosphate. Rather, it appears that antimycin A increases CO(2) fixation rate by indirectly stimulating the enzyme, ribulose-1,5-diphosphate carboxylase (E.C. 4.1.1.39), which mediates the carboxylation of ribulose-1,5-diphosphate to give 3-phosphoglycerate. Another rate-limiting enzyme of the reductive pentose phosphate cycle, hexose diphosphatase (E.C. 3.1.3.11), seems also to be stimulated. The synthesis of polysaccharides (mostly starch) seems also to be stimulated. These results are interpreted as indicating that antimycin A addition enhances the general activation of those enzymes which already are activated during photosynthesis but are inactive in the dark. The ratio of adenosine triphosphate-adenosine diphosphate under conditions of photosynthesis was only moderately decreased in the presence of antimycin A, perhaps accounting in part for an observed increase in accumulation of 3-phosphoglycerate as compared with dihydroxyacetone phosphate. No significant effect on movement of metabolites from the chloroplast to the medium was seen.

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PubMed1972

Estimation of the transport and carboxylation components of the intracellular limitation to leaf photosynthesis.

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.

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