Abstract
In this paper we analyzed changes in the concentration of the three carboxylic acids (malic acid, citric acid and isocitric acid) during the salinity-induced C3–CAM shift in Mesembryanthemum crystallinum. We documented that a nocturnal accumulation of citrate preceded that of malate, and that the CAM-dependent increase in citric acid was about 100–times higher than that of malic acid. The induction of CAM was accompanied by an increased activity of cytosolic NADP-dependent isocitrate dehydrogenase (NADP-ICDH, E.C 1.1.1.42) and by decreased activities of mitochondrial enzymes: fumarase (E.C 4.2.1.2) and NAD-dependent ICDH (E.C 1.1.1.41). Moreover, the activity of citrate synthase (E.C 2.3.3.1) was increased during the nocturnal phase of CAM. Altogether, obtained data suggest that some part of the product of a primary carboxylation (oxaloacetic acid) may pass through the mitochondria at night for reduction and, in form of citrate and isocitrate, may leave the mitochondria to support a daytime decarboxylation.
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