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  • 1
    Electronic Resource
    Electronic Resource
    Adenine nucleotides and the xanthophyll cycle in leaves (1994)
    Springer
    Planta 192 (1994), S. 526-536 
    Details
    ISSN: 1432-2048
    Keywords: Adenylate energy charge ; Adenylate kinase equilibrium ; Aegialitis ; Gossypium ; Photosynthesis ; Stress (low temperature, low CO2) ; Xanthophyll cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of varying the steady-state rate of non-cyclic photosynthetic electron transport on the leaf adenylate energy charge and the epoxidation state of the xanthophyll-cycle pigments were determined in leaves of cotton (Gossypium hirsutum L.) and the mangrove (Aegialitis annulata R.Br.). Different photosynthetic rates were obtained by varying the intercellular CO2 concentration and/or the leaf temperature, and in some cases, by changing the leaf conductance to CO2 diffusion. Also determined were the effects of these treatments on the changes in the adenylate energy charge and the epoxidation state of the xanthophyll-cycle pigments that occur after darkening of the leaves. The leaf adenylate pool remained close to equilibrium with the adenylate kinase both in the light at steady state and during dark relaxation. The adenylate energy charge increased as the photosynthetic rate decreased and maximal levels were obtained when CO2 assimilation and, therefore, non-cyclic electron flow were maximally inhibited. This implies that, in nature, photophosphorylation may provide energy needed for ion-pumping and biosynthetic and repair processes, even under stress conditions that severely restrict or prevent photosynthetic gas exchange. High levels of de-epoxidized violaxanthin in the light did not necessarily indicate or depend on a high adenylate energy charge. Dithiothreitol, an inhibitor of the violaxanthin de-epoxidase a nd ascorbate peroxidase, did not inhibit the adenylate energy charge in the light. Thus we conclude that coupled electron transport during inhibited CO2 fixation was not driven by a dithiothreitol-sensitive Mehler ascorbate-peroxidase reaction. The changes in the adenylate energy charge and xanthophyll re-epoxidation that follow when leaves were darkened are strongly affected by the preceding photosynthetic rate. Postillumination fluctuations in adenylate energy charge, both at 15 ° and 27 °C, were most pronounced when the preceding photosynthetic rate was minimal and least pronounced when this rate was maximal. Temperature had a considerably greater influence in the dark on xanthophyll re-epoxidation than on the pattern of adenylate relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203591
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Adenine nucleotides and the xanthophyll cycle in leaves (1994)
    Springer
    Planta 192 (1994), S. 537-544 
    Details
    ISSN: 1432-2048
    Keywords: Adenylate energy charge ; ATPase activity ; Energy dissipation ; Gossypium ; Photosynthesis ; Stress (low temperature, low CO2) ; xanthophyll cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The relationships among the leaf adenylate energy charge, the xanthophyll-cycle components, and photosystem II (PSII) fluorescence quenching were determined in leaves of cotton (Gossypium hirsutum L. cv. Acala) under different leaf temperatures and different intercellular CO2 concentrations (Ci). Attenuating the rate of photosynthesis by lowering the Ci at a given temperature and photon flux density increased the concentration of high-energy adenylate phosphate bonds (adenylate energy charge) in the cell by restricting ATP consumption (A.M. Gilmore, O. Björkman 1994, Planta 192, 526–536). In this study we show that decreases in photosynthesis and increases in the adenylate energy charge at steady state were both correlated with decreases in PSII photo-chemical efficiency as determined by chlorophyll fluorescence analysis. Attenuating photosynthesis by decreasing Ci also stimulated violaxanthin-de-epoxidation-dependent nonradiative dissipation (NRD) of excess energy in PSII, measured by nonphotochemical fluorescence quenching. However, high NRD levels, which indicate a large trans-thylakoid proton gradient, were not dependent on a high adenylate energy charge, especially at low temperatures. Moreover, dithiothreitol at concentrations sufficient to fully inhibit violaxanthin de-epoxidation and strongly inhibit NRD, affected neither the increased adenylate energy charge nor the decreased PSII photo-chemical efficiency that result from inhibiting photosynthesis. The build-up of a high adenylate energy charge in the light that took place at low Ci and low temperatures was accompanied by a slowing of the relaxation of non-photochemical fluorescence quenching after darkening. This slowly relaxing component of nonphotochemical quenching was also correlated with a sustained high adenylate energy charge in the dark. These results indicate that hydrolysis of ATP that accumulated in the light may acidify the lumen and thus sustain the level of NRD for extended periods after darkening the leaf. Hence, sustained nonphotochemical quenching often observed in leaves subjected to stress, rather than being indicative of photoinhibitory damage, apparently reflects the continued operation of NRD, a photoprotective process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203592
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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