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. Post-translationally inactivated by cysteine-mediated redox modification via the ferredoxin-thioredoxin system in the light and this avoids futile cycles with photosynthetic CO2 fixation. 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 (By similarity). Interacts with G6PD1 (PubMed:21309870). Expressed in roots, leaves, stems, buds, flowers and siliques. Increase of activity in the apex linked to the early stages of the transition from vegetative to reproductive growth. There are 6 glucose-6-phosphate 1-dehydrogenase genes in A.thaliana. Belongs to the glucose-6-phosphate dehydrogenase family.