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  • Articles: DFG German National Licenses  (2)
  • C3  (2)
  • 1
    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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  • 2
    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
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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