Post-translational Regulation of Enzymes from Sugar-alcohols Metabolism in Plants

M.D. HARTMAN; C.M. FIGUEROA; A.A. IGLESIAS

Mar del Plata

Congreso; XXIX Reunión Anual de Fisiología Vegetal; 2012

Sociedad Argentina de Fisiología Vegetal

POST-TRANSLATIONAL REGULATION OF ENZYMES FROM SUGAR-ALCOHOLS METABOLISM IN PLANTS Author´sMatías Daniel Hartman1 ; Carlos María Figueroa1 ; Alberto Álvaro Iglesias1 Affiliations:1 Instituto de Agrobiotecnología del Litoral (IAL-UNL-CONICET), Santa Fe, Argentina mdhartman@fbcb.unl.edu.ar In addition to starch and sucrose, many species from the Rosaceae family produce important amounts of glucitol (Gol). In mature leaves, glucose-6P is converted into Gol-6P by aldose-6P reductase (Ald-6PRase). Subsequently, the phosphate group is hydrolyzed by a specific phosphatase and Gol is transferred to sink tissues, where it is oxidized to fructose by Gol dehydrogenase (GolDHase). To gain information on the regulation of sugar-alcohols metabolism in these plants we studied post-translational modification of peach Ald-6PRase and GolDHase. Ald-6PRase was recovered from leaves using a ferric affinity chromatography, which indicates that it is phosphorylated in vivo. Utilizing [32P]ATP and a protein extract from peach leaves we found that recombinant Ald-6PRase is phosphorylated in vitro. The protein kinase specifically involved was partially purified and found to be inhibited by pyrophosphate, fructose-1,6-bisP, phosphoenolpyruvate, Gol-6P and glucose-6P (I0.5 values of 0.49, 1.9, 2.1, 3.3 and 7.7 mM, respectively). Considering that intracellular levels of these metabolites and Ald-6PRase activity fluctuate during the photoperiod, it is tempting to speculate that the latter could be light/dark modulated in vivo through protein phosphorylation. On the other hand, recombinant GolDHase was highly inhibited by oxidizing reagents like diamide, hydrogen peroxide, and oxidized glutathione; whereas the activity of the oxidized enzyme was recovered by reduction with DTT, reduced glutathione, and recombinant thioredoxin h (TRXh, from peach fruits). Since Gol accumulation has been related with abiotic stress tolerance, we hypothesize that GolDHase could be inhibited under oxidative environment conditions, thus maintaining levels of Gol high enough to exert a protective role as a hydroxyl-radical scavenger. As a whole, our results suggest that Ald-6PRase and GolDHase from peach could be key targets for in vivo post-translational regulation