The structure and function of the thylakoid membrane

Abstract

Thylakoid membranes are laterally differentiated into appressed and non-appressed regions called grana and stroma lamellae. Pure stroma lamellae isolated from wild type maize and barley leaves contain photosystem I and its light-harvesting antennae, the cytochromeb6/f complex and coupling factor. Maize stroma lamellae contained only 2% of the total photosystem II polypeptides found in whole thylakoids, and most of the small amount of the photosystem II light-harvesting complex (LHCII) was associated with photosystem I. These results were consistent with the low rates of photosystem II electron transport and low levels of the high potential form of cytochromeb-559. Immune blot assays indicated that about half of the low potential form of cytochromeb-559 in stroma lamellae was antigenically distinct from that derived from the high potential form. The amount of LHCII in stroma lamellae could be increased by exposing leaves to bright white light (state 2) prior to the isolation of stromal lamellae. This LHCII caused a 15% increase in photosystem I antenna size and was different from the LHCII found in grana lamellae, since it lacked a 26 kD polypeptide possibly involved in thylakoid appression. These results demonstrate that the migration of LHCII from appressed to non-appressed lamellae as a result of changes in the relative amounts of energy absorbed by the 2 different photosystems, also occurs in vivo.