Planta

, Volume 183, Issue 4, pp 555–566

Decreased ribulose-1,5-bisphosphate carboxylase-oxygenase in transgenic tobacco transformed with ‘antisense’ rbcS

II. Flux-control coefficients for photosynthesis in varying light, CO2, and air humidity
  • M. Stitt
  • W. P. Quick
  • U. Schurr
  • E.-D. Schulze
  • S. R. Rodermel
  • L. Bogorad
Article

DOI: 10.1007/BF00194277

Cite this article as:
Stitt, M., Quick, W.P., Schurr, U. et al. Planta (1991) 183: 555. doi:10.1007/BF00194277

Abstract

Transgenic tobacco (Nicotiana tabacum L.) plants transformed with ‘antisense’ rbcS to produce a series of plants with a progressive decrease in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been used to investigate the contribution of Rubsico to the control of photosynthesis at different irradiance, CO2 concentrations and vapour-pressure deficits. Assimilation rates, transpiration, the internal CO2 concentration and chlorophyll fluorescence were measured in each plant. (i) The flux-control coefficient of Rubisco was estimated from the slope of the plot of Rubisco content versus assimilation rate. The flux-control coefficient had a value of 0.8 or more in high irradiance, (1050 μmol·m−2·s−1), low-vapour pressure deficit (4 mbar) and ambient CO2 (350 μbar). Control was marginal in enhanced CO2 (450 μbar) or low light (310 μmol·m−2·s−1) and was also decreased at high vapour-pressure deficit (17 mbar). No control was exerted in 5% CO2. (ii) The flux-control coefficients of Rubisco were compared with the fractional demand placed on the calculated available Rubisco capacity. Only a marginal control on photosynthetic flux is exerted by Rubisco until over 50% of the available capacity is being used. Control increases as utilisation rises to 80%, and approaches unity (i.e. strict limitation) when more than 80% of the available capacity is being used. (iii) In low light, plants with reduced Rubisco have very high energy-dependent quenching of chlorophyll fluorescence (qE) and a decreased apparent quantum yield. It is argued that Rubisco still exerts marginal control in these conditions because decreased Rubisco leads to increased thylakoid energisation and high-energy dependent dissipation of light energy, and lower light-harvesting efficiency. (iv) The flux-control coefficient of stomata for photosynthesis was calculated from the flux-control coefficient of Rubisco and the internal CO2 concentration, by applying the connectivity theorem. Control by the stomata varies between zero and about 0.25. It is increased by increased irradiance, decreased CO2 or decreased vapour-pressure deficit. (v) Photosynthetic oscillations in saturating irradiance and CO2 are suppressed in decreased-activity transformants before the steady-state rate of photosynthesis is affected. This provides direct evidence that these oscillations reveal the presence of “excess” Rubisco. (vi) Comparison of the flux-control coefficients of Rubisco with mechanistic models of photosynthesis provides direct support for the reliability of these models in conditions where Rubisco has a flux-control coefficient approach unity (i.e. “limits” photosynthesis), but also indicates that these models are less useful in conditions where control is shared between Rubisco and other components of the photosynthetic apparatus.

Key words

Flux control (photosynthesis) Nicotiana (transformed with antisense DNA) Ribulose-1,5-bisphosphate carboxylase-oxygenase (control of photosynthesis) Transgenic plant (antisense) 

Abbreviations

A

assimilation rate

Ci

intercellular CO2 concentration in the leaf

CR

flux-control coefficient of Rubisco for photosynthesis

qE

high-energy-state-dependent quenching of chlorophyll fluorescence

QA

primary acceptor of PSII

rbc S

gene for the nuclear-encoded small subunit of Rubisco

Rubisco

ribulose-1,5-bisphosphate carboxylase-oxygenase

Ru1,5bisP

ribulose-1,5-bisphosphate

VPD

vapour-pressure deficit

Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • M. Stitt
    • 1
  • W. P. Quick
    • 1
  • U. Schurr
    • 2
  • E.-D. Schulze
    • 2
  • S. R. Rodermel
    • 3
  • L. Bogorad
    • 3
  1. 1.Lehrstuhl für PflanzenphysiologieUniversität BayreuthBayreuthFederal Republic of Germany
  2. 2.Lehrstuhl für PflanzenökologieUniversität BayreuthBayreuthFederal Republic of Germany
  3. 3.The Biological Laboratories, Harvard UniversityCambridgeUSA

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