Post-translational regulation of enzymes from sugar-alcohols metabolism in plants

HARTMAN MD; FIGUEROA CM; IGLESIAS AA

Mar del Plata

Congreso; XXIX Reunión Argentina de Fisiología Vegetal; 2012

Sociedad Argentina de Fisiología Vegetal

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 modifications of peach Ald-6PRase and GolDHase. Ald-6PRase was recovered using a Fe3+-affinity chromatography, which suggests that it could be phosphorylated in vivo. Utilizing [32P]ATP and a protein extract from peach leaves we found that recombinant Ald 6PRase is phosphorylated in vitro. The partially purified PKase was inhibited by pyrophosphate, fructose-1,6-bisP, phosphoenolpyruvate, Gol-6P and glucose-6P (I0.5 values were 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.We also found that recombinant GolDHase was highly inhibited by oxidizing reagents like diamide, H2O2, and oxidized glutathione (k´´ values were 12.3, 6.93 and 0.086 M-1 s-1, respectively); whereas the activity of the oxidized enzyme was recovered by reduction with DTT, reduced glutathione, and recombinant thioredoxin h (TRXh) from peach fruits. Considering that 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.