, Volume 197, Issue 3, pp 482–489

Increased capacity for photosynthesis in wheat grown at elevated CO2: the relationship between electron transport and carbon metabolism

  • Dimah Z. Habash
  • Matthew J. Paul
  • Martin A. J. Parry
  • Alfred J. Keys
  • David W. Lawlor

DOI: 10.1007/BF00196670

Cite this article as:
Habash, D.Z., Paul, M.J., Parry, M.A.J. et al. Planta (1995) 197: 482. doi:10.1007/BF00196670


Spring wheat (Triticum aestivum L.) was grown under optimal nutrition for six weeks at 700 and 350 μmol·mol−1 CO2 and simultaneous measurements of photosystem-II (PSII) chlorophyll fluorescence and gas exchange were conducted on intact attached leaves. Plants grown at elevated CO2 had double the concentration of CO2 at the carboxylation site (Cc) despite a lowered stomatal (gs) and mesophyll (gm) conductance compared with ambient-grown plants. Plants grown at elevated CO2 had a higher relative quantum yield of PSII electron transport (ΦPSII) and a higher relative quantum yield of CO2 fixation (ΦCO2). The higher ΦPSII was due to a larger proportion of open PSII centres, estimated by the coefficient of photochemical quenching of fluorescence (qp), with no change in the efficiency of light harvesting and energy transduction by open PSII centres (F′v/F′m). Analysis of the relationship between ΦPSII and ΦCO2 conducted under various CO2 and O2 concentrations showed that the higher ΦCO2 for a given ΦPSII in leaves developed under elevated CO2 was similar to that obtained in leaves upon a partial reduction in photorespiration. Calculation of the allocation of photosynthetic electron-transport products to CO2 and O2 showed that for leaves developed in elevated CO2, there was an increase in both total linear electron flow and electron flow to CO2 and a decrease in electron flow to O2. Plants developed under elevated CO2 showed positive acclimation manifested by a higher ΦCO2 when measured under ambient CO2 and higher assimilation rates in A/Ci curves. Initial and total activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco EC measured in vitro increased by 16 and 15% respectively in leaves from plants grown in elevated CO2, which was in agreement with a 15% higher in vivo carboxylation efficiency. It is concluded that growth of spring wheat at elevated CO2 enhances photosynthesis due to a change in the balance of component processes manifested as an increased capacity for carbon fixation, total electron transport and Rubisco activity, and a concomitant partial reduction of photorespiration.

Key words

Carbon assimilation Chlorophyll fluorescence Electron transport Elevated CO2 Photosynthesis Triticum (photosynthesis) 

Abreviations and Symbols


net CO2 assimilation


CO2 concentration at the site of carboxylation


intercellular CO2 concentration

Fm, F′m

maximum fluorescence after 1 h dark adaptation, under steady-state light conditions

Fv, F′v

variable fluorescence after 1 h dark adaptation, under steady-state light conditions


fluorescence at steady state in the light


total linear electron flow


linear electron flow allocated to CO2 assimilation


linear electron flow allocated to O2 reduction


photon flux density

qp, qN

coefficients for photochemical, non-photochemical quenching of fluorescence

vc, vo

rates of RuBP carboxylation, RuBP oxygenation


ribulose-1,5-bisphosphate carboxylase-oxygenase


relative quantum yield of PSII electron transport


relative quantum yield of CO2 assimilation

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Dimah Z. Habash
    • 1
  • Matthew J. Paul
    • 1
  • Martin A. J. Parry
    • 1
  • Alfred J. Keys
    • 1
  • David W. Lawlor
    • 1
  1. 1.Biochemistry and Physiology DepartmentIACR-RothamstedHarpendenUK

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