An alternative model for photosystem II/light harvesting complex II in grana membranes based on cryo‐electron microscopy studies

Abstract

The photosynthetic protein complexes in plants are located in the chloroplast thylakoid membranes. These membranes have an ultrastructure that consists of tightly stacked ÔgranaÕ regions interconnected by unstacked membrane regions. The structure of isolated grana membranes has been studied here by cryo-electron microscopy. The data reveals an unusual arrangement of the photosynthetic protein complexes, staggered over two tightly stacked planes. Chaotrope treatment of the paired grana membranes has allowed the separation and isolation of two biochemically distinct membrane fractions. These data have led us to an alternative model of the ultrastructure of the grana where segregation exists within the grana itself. This arrangement would change the existing view of plant photosynthesis, and suggests potential links between cyanobacterial and plant photosystem II light harvesting systems.

Light-harvesting and structural organization of Photosystem II: From individual complexes to thylakoid membrane

“…Where are these trimers located? It has been proposed that part of the LHCII antenna is located in different membrane layers containing only LHCII trimers [158]. However, recent tomography results seem to exclude this possibility [135,149].…”

Three-Dimensional Organization of Higher-Plant Chloroplast Thylakoid Membranes Revealed by Electron Tomography

“…Future research should concentrate on the structure of thylakoids exposed to PSII-specific light, where the exact nature of membrane unstacking and other rearrangements associated with state transitions can be determined. One may also use electron microscopy techniques to determine the organization of photosynthetic complexes and supercomplexes in the thylakoid membranes under different conditions of illumination (Boekema et al, 2000;Ford et al, 2002;Kirchhoff et al, 2004). The information obtained from such analyses can be combined with data derived from other high-resolution imaging methods, such as atomic force microscopy (Kaftan et al, 2002), as well as from x-ray crystallography to provide a detailed picture of the macroscopic and microscopic makeup of the photosynthetic apparatus, which can then be correlated to its activity and light adaptability.…”

Thermo-optically Induced Reorganizations in the Main Light Harvesting Antenna of Plants. II. Indications for the Role of LHCII-only Macrodomains in Thylakoids

“…With regard to the origin of these close similarities in the 'static and dynamic' features of loosely stacked lamellar aggregates of LHCII and granal thylakoid membranes, recent models of the organization of LHCII and LHCII-PS II particles in granal thylakoids are of special interest (Boekema et al 2000;Ford et al 2002;Dekker and Boekema 2005). These models, derived from electron microscopy analysis, depict the granum thylakoid membranes to contain two large domains, which are adjacent to each other: an extended area containing ordered arrays of LHCII-PS II supercomplexes, which however contain substoichiometric amounts of LHCII, and an LHCII-only macrodomain, which contains, also in highly ordered arrays, the 'missing' light harvesting complexes.…”