Assimilation of CO2, enzyme activation and photosynthetic electron transport in bean leaves, as affected by high light and ozone

Authors

  • L. Guidi,

    Corresponding author
    1. Dipartimento di Chimica e Biotecnologie Agrarie, Università di Pisa, Via del Borghetto 80, I–56124 Pisa, Italy
      Author for correspondence: L. Guidi Tel: +39 50 9719320 Fax: +39 50 598614 Email: guidilu@agr.unipi.it
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  • E. Degl’Innocenti,

    1. Dipartimento di Chimica e Biotecnologie Agrarie, Università di Pisa, Via del Borghetto 80, I–56124 Pisa, Italy
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  • G. F. Soldatini

    1. Dipartimento di Chimica e Biotecnologie Agrarie, Università di Pisa, Via del Borghetto 80, I–56124 Pisa, Italy
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Author for correspondence: L. Guidi Tel: +39 50 9719320 Fax: +39 50 598614 Email: guidilu@agr.unipi.it

Summary

  • •   Bean seedlings (Phaseolus vulgaris cv. Pinto) were grown in the greenhouse at a light intensity of 400 µmol m−2 s−1. When the primary leaf was fully expanded, plants were divided into four groups and subjected to one of the following treatments: light intensity of 400 µmol m−2 s−1 and filtered air (control); light intensity of 400 µmol m−2 s−1 and ozone (O3) (150 nl l−1 for 5 h) (ozonated); light intensity of 1000 µmol m−2 s−1 for 5 h and filtered air (HL); and light intensity of 1000 µmol m−2 s−1 and O3 (150 nl l−1) for 5 h (HL + O3).
  • •   At the end of the treatments (HL and/or O3) a strong decrease in CO2 assimilation rate as well a decrease in stomatal conductance were observed, while no changes in intercellular CO2 concentration were recorded. In addition the Fv : Fm ratio (maximal quantum yield for PSII photochemistry) decreased in the stressed leaves (HL and/or O3), indicating photoinhibition, and they showed a corresponding increase in minimal fluorescence (F0), indicating a higher number of deactivating photosystem II (PSII) centres.
  • •   The maximum catalytic activity of the Benson–Calvin cycle enzymes, fructose-1,6-bisphosphate phosphatase (FBPase) and Rubisco, decreased following HL + O3 stress but activation was enhanced. A linear relation was found between activation state of NADP-malate dehydrogenase (MDH) and the flux of electrons through PSII and in HL + O3-treated plants NADP-MDH activity decreased at high irradiance levels, indicating a limitation in linear electron flux.

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