etioplastides esinev membraanitorude võrestik, mis valguses kujuneb tülakoidide membraanideks ja moodustab graanid, The disorganised membrane aggregations in chloroplasts that have been deprived of light (etioplasts). They are converted to chloroplasts via the stimulation of chlorophyll synthesis by the plant hormone cytokinin soon after exposure to light. Thylakoids and grana arise from the prolamellar bodies during this process.