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

Abstract

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 (ΦCO 2). 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 ΦCO 2 conducted under various CO2 and O2 concentrations showed that the higher ΦCO 2 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 ΦCO 2 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 4.1.1.39) 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.

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Abbreviations

A:

net CO2 assimilation

Cc :

CO2 concentration at the site of carboxylation

Ci :

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

Fs :

fluorescence at steady state in the light

J1 :

total linear electron flow

JA :

linear electron flow allocated to CO2 assimilation

JL :

linear electron flow allocated to O2 reduction

PFD:

photon flux density

qp, qN :

coefficients for photochemical, non-photochemical quenching of fluorescence

vc, vo :

rates of RuBP carboxylation, RuBP oxygenation

Rubisco:

ribulose-1,5-bisphosphate carboxylase-oxygenase

ΦPSII :

relative quantum yield of PSII electron transport

ΦCO 2 :

relative quantum yield of CO2 assimilation

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Correspondence to Dimah Z. Habash.

Additional information

We would like to thank Simon Driscoll and Valerie Mitchell for technical assistance, Rowan Mitchell and Tony Goodwin for help in curve-fitting and Bernard Genty (Laboratoire d'Ecologie Végétale, Universite De Paris XI, Orsay, France) for critical comments on the manuscript. This work was supported by a grant from the Biotechnology and Biological Sciences Research Council (Agricultural and Food Research Council).

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Habash, D.Z., Paul, M.J., Parry, M.A.J. et al. Increased capacity for photosynthesis in wheat grown at elevated CO2: the relationship between electron transport and carbon metabolism. Planta 197, 482–489 (1995). https://doi.org/10.1007/BF00196670

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  • DOI: https://doi.org/10.1007/BF00196670

Key words

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