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  • Articles: DFG German National Licenses  (4)
  • C3  (2)
  • quantum yield  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Can CO2 assimilation in maize leaves be predicted accurately from chlorophyll fluorescence analysis? (1993)
    Springer
    Photosynthesis research 37 (1993), S. 89-102 
    Details
    ISSN: 1573-5079
    Keywords: C4 photosynthesis ; chlorophyll fluorescence ; CO2 assimilation ; maize ; Photosystem II ; quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Analysis is made of the energetics of CO2 fixation, the photochemical quantum requirement per CO2 fixed, and sinks for utilising reductive power in the C4 plant maize. CO2 assimilation is the primary sink for energy derived from photochemistry, whereas photorespiration and nitrogen assimilation are relatively small sinks, particularly in developed leaves. Measurement of O2 exchange by mass spectrometry and CO2 exchange by infrared gas analysis under varying levels of CO2 indicate that there is a very close relationship between the true rate of O2 evolution from PS II and the net rate of CO2 fixation. Consideration is given to measurements of the quantum yields of PS II (φ PS II) from fluorescence analysis and of CO2 assimilation ( $$\phi _{CO_2 } $$ ) in maize over a wide range of conditions. The $${{\phi _{PSII} } \mathord{\left/ {\vphantom {{\phi _{PSII} } {\phi _{CO_2 } }}} \right. \kern-\nulldelimiterspace} {\phi _{CO_2 } }}$$ ratio was found to remain reasonably constant (ca. 12) over a range of physiological conditions in developed leaves, with varying temperature, CO2 concentrations, light intensities (from 5% to 100% of full sunlight), and following photoinhibition under high light and low temperature. A simple model for predicting CO2 assimilation from fluorescence parameters is presented and evaluated. It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO2 assimilation rates in maize.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02187468
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Light/dark modulation of phosphoenolpyruvate carboxylase in C3 and C4 species (1994)
    Springer
    Photosynthesis research 42 (1994), S. 133-143 
    Details
    ISSN: 1573-5079
    Keywords: PEP carboxylase ; C3 ; C4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In this report, the effects of light on the activity and allosteric properties of phosphoenolpyruvate (PEP) carboxylase were examined in newly matured leaves of several C3 and C4 species. Illumination of previously darkened leaves increased the enzyme activity 1.1 to 1.3 fold in C3 species and 1.4 to 2.3 fold in C4 species, when assayed under suboptimal conditions (pH 7) without allosteric effectors. The sensitivities of PEP carboxylase to the allosteric effectors malate and glucose-6-phosphate were markedly different between C3 and C4 species. In the presence of 5 mM malate, the activity of the enzyme extracted from illuminated leaves was 3 to 10 fold higher than that from darkened leaves in C4 species due to reduced malate inhibition of the enzyme from illuminated leaves, whereas it increased only slightly in C3 species. The Ki(malate) for the enzyme increased about 3 fold by illumination in C4 species, but increased only slightly in C3 species. Also, the addition of the positive effector glucose-6-phosphate provided much greater protection against malate inhibition of the enzyme from C4 species than C3 species. Feeding nitrate to excised leaves of nitrogen deficient plants enhanced the degree of light activation of PEP carboxylase in the C4 species maize, but had little or no effect in the C3 species wheat. These results suggest that post-translational modification by light affects the activity and allosteric properties of PEP carboxylase to a much greater extend in C4 than in C3 species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02187124
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Light dependence of quantum yields of Photosystem II and CO2 fixation in C3 and C4 plants (1993)
    Springer
    Photosynthesis research 35 (1993), S. 265-274 
    Details
    ISSN: 1573-5079
    Keywords: C3 plants ; C4 plants ; light ; Photosystem II ; quantum yield ; fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The light dependence of quantum yields of Photosystem II (ΦII) and of CO2 fixation were determined in C3 and C4 plants under atmospheric conditions where photorespiration was minimal. Calculations were made of the apparent quantum yield for CO2 fixation by dividing the measured rate of photosynthesis by the absorbed light [A/I=ΦCO2 and of the true quantum yield by dividing the estimated true rate of photosynthesis by absorbed light [(A+Rl)/Ia=ΦCO2·], where RL is the rate of respiration in the light. The dependence of the ΦII/ΦCO2 and ΦII/ΦCO2 * ratios on light intensity was then evaluated. In both C3 and C4 plants there was little change in the ratio of ΦII/ΦCO2 at light intensities equivalent to 10–100% of full sunlight, whereas there was a dramatic increase in the ratio at lower light intensities. Changes in the ratio of ΦII/ΦCO2 can occur because respiratory losses are not accounted for, due to changes in the partitioning of energy between photosystems or changes in the relationship between PS II activity and CO2 fixation. The apparent decrease in efficiency of utilization of energy derived from PS II for CO2 fixation under low light intensity may be due to respiratory loss of CO2. Using dark respiration as an estimate of RL, the calculated ΦII/ΦCO2 * ratio was nearly constant from full sunlight down to approx 5% of full sunlight, which suggests a strong linkage between the true rate of CO2 fixation and PS II activity under varying light intensity. Measurements of photosynthesis rates and ΦII were made by illuminating upper versus lower leaf surfaces of representative C3 and C4 monocots and dicots. With the monocots, the rate of photosynthesis and the ratio of ΦII/ΦCO2 exhibited a very similar patterns with leaves illuminated from the adaxial versus the abaxial surface, which may be due to uniformity in anatomy and lack of differences in light acclimation between the two surfaces. With dicots, the abaxial surface had both lower rates of photosynthesis and lower ΦII values than the adaxial surface which may be due to differences in anatomy (spongy versus palisade mesophyll cells) and/or light acclimation between the two surfaces. However, in each species the response of ΦII/ΦCO2 to varying light intensity was similar between the two surfaces, indicating a comparable linkage between PS II activity and CO2 fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00016557
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Malate metabolism by NADP-malic enzyme in plant defense (1999)
    Springer
    Photosynthesis research 61 (1999), S. 99-105 
    Details
    ISSN: 1573-5079
    Keywords: C3 ; C4 ; UV-B ; stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Malate is involved in various metabolic pathways, and there are several enzymes that metabolize it. One important malate metabolizing enzyme is NADP-malic enzyme (NADP-ME). NADP-ME functions in many different pathways in plants, having an important role in C4 photosynthesis where it releases the CO2 to be used in carbon fixation by Rubisco. Apart from this specialized role, NADP-ME is thought to fulfill diverse housekeeping functions because of its universal presence in different plant tissues. NADP-ME is induced after wounding or exposure to UV-B radiation. In this way, the enzyme is implicated in defense-related deposition of lignin by providing NADPH for the two NADPH-dependent reductive steps in monolignol biosynthesis. On the other hand, it can supply NADPH for flavonoid biosynthesis as many steps in the flavonoid biosynthesis pathway require reductive power. Pyruvate, another product of NADP-ME reaction, can be used for obtaining ATP through respiration in the mitochondria; and may serve as a precursor for synthesis of phosphoenolpyruvate (PEP). PEP is utilized in the shikimate pathway, leading to the synthesis of aromatic amino acids including phenylalanine, the common substrate for lignin and flavonoid synthesis. Moreover, NADP-ME can be involved in mechanisms producing NADPH for synthesis of activated oxygen species that are produced in order to kill or damage pathogens. In conclusion, an increase in the levels of NADP-ME could provide building blocks and energy for biosynthesis of defense compounds, suggesting a role of malate metabolism in plant defense.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006209003096
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    Paper (German National Licenses)
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