The glucan phosphorylation mediated by α-glucan, water dikinase (GWD) is also essential in the light phase for a functional transitory starch turn-over.

Starch phosphorylation mediated by the α-glucan, water dikinase (GWD) is crucial for transitory starch metabolism. The impact of the GWD action on transitory starch metabolism was analyzed in Arabidopsis mutants either lacking or revealing different reduced levels of GWD activity. In these mutants, glucose 6-phosphate (G6P) levels of the transitory leaf starch, the average leaf starch content, as well as alterations in the growth phenotype were determined under different light length conditions, including continuous light. Based on biochemical and growth phenotypical data, we found that the length of the light phase affects the phosphorylation state of the transitory starch and, by this, the average leaf starch content and the resulting growth of the plants. Additionally, we discuss data referring to an involvement of the GWD mediated glucan phosphorylation in starch synthesis, as, e.g., starch phosphorylation occurred even when a dark phase was omitted.