Granal thylakoid structure and function: explaining an enduring mystery of higher plants

What is it about?

A longstanding mystery in plant science is thylakoid grana stacks which separate photosystems in higher plants. Grana stacks are inessential for photosynthesis and appear to decrease photosynthetic electron transport efficiency. We propose that grana stacks allow plants to apply ultrastructural control on electron transport through thylakoid swelling/shrinking induced by osmotic water fluxes. This control coordinates with guard cell turgor and stomatal conductance to balance different stages of photosynthesis which vary vastly in reaction speeds. Like bellows expanding volume control of accordions on sound articulation in melodies and accompaniments, grana stacks expand volume control of thylakoids on electron transport and photosynthesis. Our theory unifies well-known phenomena of thylakoid structure and function of higher plants adapted to dry and fluctuating light environments. 

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