Malate metabolism and reactions of oxidoreduction in cold-hardened winter rye (Secale cereale L.) leaves.
In cold-hardened leaves (CHL) of winter rye (Secale cereale L.) much higher levels of malate were detected by (13)C-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 degrees C to 22 degrees C. The malate content was further increased when CHL were exposed to a higher light intensity at 4 degrees C. In CO(2)-free air the malate content of CHL strongly declined at 4 degrees C. Malate may thus serve as an additional carbon sink and as a CO(2)-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.
Crecelius
Frauke
F
Botanisches Institut, Goethe-Universität, PO Box 111932, D-60054 Frankfurt am Main, Germany.
Streb
Peter
P
Feierabend
Jürgen
J
D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D003080:Cold Temperature; D003600:Cytosol / Q000201:enzymology; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008291:Malate Dehydrogenase / Q000378:metabolism; D050538:Malate Dehydrogenase (NADP+); D008293:Malates / Q000737:chemistry / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects / Q000528:radiation effects; D010269:Paraquat / Q000494:pharmacology; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism*; D012434:Secale / Q000201:enzymology / Q000378:metabolism*
D002247:Carbon Isotopes; D008293:Malates; D002245:Carbon Dioxide; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D050538:Malate Dehydrogenase (NADP+); D010730:Phosphoenolpyruvate Carboxylase; D010269:Paraquat