Fig. 6. A model of membrane unstacking. (A) Cross-section of the thylakoid stacks. (B) Top view. Unstacking begins by evagination of the membranes located at the stromal-exposed edges of the appressed grana domains (top). As unfolding proceeds, membranes are pulled from the stack’s interior towards the edges, allowing for an increase in lateral dimensions with no change in height (middle and bottom). Eventually, the stacks merge completely with the neighbouring stroma lamellae, and grana topology is lost (Figure 4C).