Journal of Experimental Botany, Vol. 54, No. 384, pp. 1075-1083,
March 1, 2003
© 2003 Oxford University Press
Malate metabolism and reactions of oxidoreduction in cold-hardened winter rye (Secale cereale L.) leaves
Received 15 October 2002; Accepted 21 November 2002
1 Botanisches Institut, Goethe-Universität, PO Box 111932, D-60054 Frankfurt am Main, Germany
2 Laboratoire d’Ecophysiologie Végétale, Bâtiment 362, UFR Scientifique d’Orsay, Université Paris XI, F-91405 Orsay Cedex, France
3 To whom correspondence should be addressed. Fax: +49 69 79824822. E-mail: Feierabend{at}em.uni-frankfurt.de
Abbreviations: CHL, cold-hardened leaves; NHL, non-hardened leaves; NMR, nuclear-magnetic resonance spetroscopy; PEPCase, phosphoenolpyruvate carboxylase; PPDK, pyruvate;orthophosphate dikinase; ROS, reactive oxygen species.
In cold-hardened leaves (CHL) of winter rye (Secale cereale L.) much higher levels of malate were detected by 13C-NMR than in non-hardened leaves (NHL). As this was not observed previously, malate metabolism of CHL was studied in more detail by biochemical assays. The activities of several enzymes of malate metabolism, NADP-malate dehydrogenase, NAD-malate dehydrogenase, phosphoenolpyruvate carboxylase, and NADP-malic enzyme, were also increased in CHL. Short exposures to low temperature of 1–3 d did not induce increases in the malate content or in the activities of enzymes of malate metabolism in mature NHL. The malate content and the enzyme activities declined within 1–2 d after a transfer of CHL from their growing temperature of 4 °C to 22 °C. The malate content was further increased when CHL were exposed to a higher light intensity at 4 °C. In CO2-free air the malate content of CHL strongly declined at 4 °C. Malate may thus serve as an additional carbon sink and as a CO2-store in CHL. It may further function as a vacuolar osmolyte balancing increased concentrations of soluble sugars previously observed in the cytosol of CHL. Malate was not used as a source of reductants when CHL were exposed to photo-oxidative stress by treatment with paraquat. However, the activities of enzymes of the oxidative pentose phosphate pathway were markedly increased in CHL and may serve as non-photosynthetic sources of NADPH and thus contribute to the previously observed superior capacity of CHL of winter rye to maintain their antioxidants in a reduced state in the presence of paraquat.
Key words: Cold-acclimation, malate metabolism, paraquat, pentose phosphate pathway, Secale.
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