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Photosynth Res (2008) 97:223233 DOI 10.1007/s11120-008-9329-7
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The activities of PEP carboxylase and the C4 acid decarboxylases are little changed by drought stress in three C4 grasses of different subtypes
Ana E. Carmo-Silva Anabela Bernardes da Silva Alfred J. Keys Martin A. J. Parry Maria C. Arrabaa
Received: 31 January 2008 / Accepted: 2 July 2008 / Published online: 16 July 2008 Springer Science+Business Media B.V. 2008
Abstract The C4 photosynthetic pathway involves the assimilation of CO2 by phosphoenolpyruvate carboxylase (PEPC) and the subsequent decarboxylation of C4 acids. The enzymes of the CO2 concentrating mechanism could be affected under water decit and limit C4 photosynthesis.
Three different C4 grasses were submitted to gradually induced drought stress conditions: Paspalum dilatatum (NADP-malic enzyme, NADP-ME), Cynodon dactylon (NAD-malic enzyme, NAD-ME) and Zoysia japonica (PEP carboxykinase, PEPCK). Moderate leaf dehydration affected the activity and regulation of PEPC in a similar manner in the three grasses but had species-specic effects on the C4 acid decarboxylases, NADP-ME, NAD-ME and
PEPCK, although changes in the C4 enzyme activities were small. In all three species, the PEPC phosphorylation state, judged by the inhibitory effect of L-malate on PEPC activity, increased with water decit and could promote increased assimilation of CO2 by the enzyme under stress conditions. Appreciable activity of PEPCK was observed in all three species suggesting that this enzyme may act as a supplementary decarboxylase to NADP-ME and NAD-ME in addition to its role in other metabolic pathways.
Keywords C4 grasses Drought stress NAD-ME
NADP-ME PEPC PEPCK
AbbreviationsBS Bundle sheathDTT 1,4-DithiothreitolEDTA Ethylenediaminetetraacetic acid LWP Leaf water potentialM MesophyllMDH Malate dehydrogenaseNADH Nicotinamide-adenine dinucleotide
(reduced)
NAD-ME NAD-malic enzymeNADPH Nicotinamide-adenine dinucleotide phosphate (reduced)
NADP-ME NADP-malic enzymePEG Polyethylene glycolPEP PhosphoenolpyruvatePEPC PEP carboxylasePEPCK PEP carboxykinasePPFD Photosynthetic photon ux density PVP PolyvinylpyrrolidoneRubisco RuBP carboxylase/oxygenase RuBP Ribulose-1,5-bisphosphateRWC Leaf relative water contentSWC Soil water content
Introduction
C4 photosynthesis is characterised by the presence of a CO2-concentrating mechanism, which involves the initial xation of CO2 by phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) in the mesophyll (M) cells followed
A. E. Carmo-Silva (&) A. Bernardes da Silva
M. C. ArrabaaCentro de Engenharia Biolgica and Departamento de Biologia Vegetal, Faculdade de Cincias, Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugale-mail: [email protected]
A. J. Keys M. A. J. Parry
Department of Plant Sciences, Centre...