Addition of lipid to the photosynthetic membrane: effects on membrane structure and energy transfer.

Abstract

We have carried out a series of experiments in which the lipid composition of the photosynthetic membrane has been altered by the addition of lipid from a defined source under experimental conditions . Liposomes prepared by sonication are mixed with purified photosynthetic membranes obtained from spinach chloroplasts and are taken through cycles of freezing and thawing. Several lines of evidence, including gel electrophoresis and freezefracture electron microscopy, indicate that an actual addition of lipid has taken place. Structural analysis by freeze-fracture shows that intramembrane particles are widely separated after the addition of large amounts of lipid, with one exception: large hexagonal lattices of particles appear in some regions of the membrane . These lattices are identical in appearance with lattices formed from a single purified component of the membrane known as chlorophyllprotein complex II . The suggestion that the presence of such lattices in lipid-enriched membranes reflects a profound rearrangement of photosynthetic structures has been confirmed by analysis of the fluorescence emission spectra of natural and lipid-enriched membranes. Specifically, lipid addition in each of the cases we have studied results in the apparent detachment of chlorophyll-protein complex II from photosynthetic reaction centers. It is concluded that specific arrangements of components in the photosynthetic membrane, necessary for the normal functioning of the membrane in the light reaction of photosynthesis, can be regulated to a large extent by the lipid content of the membrane .The photosynthetic membrane provides an ideal system for the study of the relationship between membrane structure and function. It is characterized by light-driven reactions which are easily assayed, as well as by a defined and highly ordered ultrastructure . The membranous sacs, or thylakoids, of the chloroplasts of higher plants have been extensively investigated by a number of workers (3,4,19). These membranes contain the machinery necessary for the light reaction of photosynthesis, involving the transport of electrons from water to appropriate acceptor molecules via a chain of electron carriers . The fundamental components of the system are two reaction centers, termed photosystem I and photosystem II . Associated with each photosystem are chlorophyll, carotenoids, and other accessory pigments.Based on freeze-fracture electron microscopy and the use of mutants or deficient plants, a rough model of the organization of the photosynthetic membrane has been constructed . For example, tobacco plants deficient in photosystem 11 lack the large (140-180 Á) particles normally observed on the so-called

Changes in fatty acid and lipid content in callus and protoplasts of Parthenocissus tricuspidata and Petunia hybrida during culture

“…This is supported by the work of Webb and Williams (1984), who showed that degradation of polar lipids in membranes occurred during isolation of protoplasts from Vicia faba. According to Siegel et al (1981) modifications in the relative quantities of lipids and proteins of highly organized membranes iike thylakoids could alter the specific spatial orientation of molecules and thus resuit in drastic alterations of the cell physiology-In order to check the relationship between the physiological state of the cells and the alteration of the membrane iipid composition, we used two protoplast sys-tems from callus cultures with a clear difference in their physiological characteristics; protoplasts from Parthenocissus tricuspidata, which are nearly devoid of mitotic activity and those from Petunia hybrida showing a high degree of microcalli fonnation. Moreover, a comparison with the original callus systems was undertaken in order to evaluate the effect of the isolation stress; Heller (1953) containing 0.25 M glucose, lO-'M Vitamin B| and 0.7% agar (Bacto agar Difco).…”

Increased Stability of LHCII by Aggregate Formation during Dark-Induced Leaf Senescence in the Arabidopsis Mutant, ore10

“…Similarly, the xanthophyll cycle pigments seem to control the organization of the LHCII , Ruban and Horton 1994, Phillip et al 1996. Specific changes in the lipid composition of the thylakoid membrane may also cause LHCII aggregation (Siegel et al 1981).…”

Excitation energy transfer in Rhodopseudomonas sphaeroides chromatophore membranes fused with liposomes

“…Overall, these results suggest that added lipid alters the organization of the membrane such that part of the B800-850 antenna becomes structurally and functionally detached from the rest of the photosynthetic unit and diffuses over the increased bilayer surface. In this connection, detachment of chlorophyll-protein complex II antenna was demonstrated recently in spinach thylakoid membranes fused with liposomes [22]. It is possible that the selective dissociation observed here may be confined to B800-850 domains at the periphery of photosynthetic units and that these B800-850 phospholipid interactions normally assist in main-taining organizational stability within the lightharvesting system.…”