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Oxygen Requirement and Inhibition of C4
Photosynthesis1
An Analysis of C4 Plants Deficient in the
C3 and C4 Cycles
João P. Maroco,
Maurice S.B. Ku,
Peter J. Lea,
Louisa V. Dever,
Richard C. Leegood,
Robert T. Furbank, and
Gerald E. Edwards*
Department of Botany, Washington State University, Pullman,
Washington 99164 (J.P.M., M.S.B.K., G.E.E.); Division of Biological
Sciences, Lancaster University, Lancaster LA1 4YQ, United Kingdom
(P.J.L., L.V.D.); Robert Hill Institute, Department of Animal and Plant
Sciences, University of Sheffield, Sheffield S10 2TN, United
Kingdom (R.C.L.); and Division of Plant Industry, Commonwealth
Scientific and Industrial Research Organization, P.O. Box 1600, Canberra ACT 2601, Australia (R.T.F.)
The basis for O2
sensitivity of C4 photosynthesis was evaluated using a
C4-cycle-limited mutant of Amaranthus edulis
(a phosphoenolpyruvate carboxylase-deficient mutant),
and a C3-cycle-limited transformant of Flaveria
bidentis (an antisense ribulose-1,5-bisphosphate
carboxylase/oxygenase [Rubisco] small subunit transformant). Data
obtained with the C4-cycle-limited mutant showed that
atmospheric levels of O2 (20 kPa) caused increased
inhibition of photosynthesis as a result of higher levels of
photorespiration. The optimal O2 partial pressure for
photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3
plants. Therefore, the higher O2 requirement for optimal
C4 photosynthesis is specifically associated with the
C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by
supraoptimal levels of O2 than in the wild type. When
CO2 fixation by Rubisco is limited, an increase in the
CO2 concentration in bundle-sheath cells via the
C4 cycle may further reduce the oxygenase activity of
Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage
and overcycling of the C4 pathway. These results indicate
that in C4 plants the investment in the C3 and
C4 cycles must be balanced for maximum efficiency.
1
J.P.M. was supported by a scholarship from Junta
Nacional de Investigação Cientifica e
Tecnológica/Praxis XXI, Lisbon, Portugal (contract no.
BD/4067/94). Portions of this work were supported in part by a National
Science Foundation grant (no. IBN 9317756 to G.E.E.) and by a
Biotechnology and Biological Science Research Council grant (no.
BR301910 to P.J.L. and R.C.L.).
*
Corresponding author; e-mail edwardsg{at}wsu.edu; fax
1-509-335-3517.
Plant Physiol. (1998) 116: 823-832
Copyright Clearance Center: 0032-0889/98/116/0823/10
© 1998 American Society of Plant Physiologists
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