Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 54, Issue 384, Pages 1075-1083Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erg101
Keywords
cold-acclimation; malate metabolism; paraquat; pentose phosphate pathway; Secale
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In cold-hardened leaves (CHL) of winter rye (Secale cereale L.) much higher levels of malate were detected by C-13-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 4degreesC to 22degreesC. The malate content was further increased when CHL were exposed to a higher light intensity at 4degreesC. In CO2-free air the malate content of CHL strongly declined at 4degreesC. 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.
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