Catalyzes the rate-limiting step of the oxidative pentose-phosphate pathway, which represents a route for the dissimilation of carbohydrates besides glycolysis (PubMed:15634201). The main function of this enzyme is to provide reducing power (NADPH) and pentose phosphates for fatty acid and nucleic acid synthesis which are involved in membrane synthesis and cell division (PubMed:15634201). D-glucose 6-phosphate + NADP(+) = 6-phospho-D-glucono-1,5-lactone + H(+) + NADPH Regulated by metabolites. Optimum pH is 8.5. Carbohydrate degradation; pentose phosphate pathway; D-ribulose 5-phosphate from D-glucose 6-phosphate (oxidative stage): step 1/3. Forms homodimer. Expressed in leaves and stems. There are 6 glucose-6-phosphate 1-dehydrogenase genes in A.thaliana. Belongs to the glucose-6-phosphate dehydrogenase family.