The acclimation of higher plants to different light intensities is associated with a reorganization of the photosynthetic apparatus. These modifications, namely, changes in the amount of peripheral antenna (LHCII) of photosystem (PS) II and changes in PSII/PSI stoichiometry, typically lead to an altered chlorophyll (Chl) a/b ratio. However, our previous studies show that in spruce, this ratio is not affected by changes in growth light intensity. The evolutionary loss of PSII antenna proteins LHCB3 and LHCB6 in the Pinaceae family is another indication that the light acclimation strategy in spruce could be different. Here we show that, unlike Arabidopsis, spruce does not modify its PSII/PSI ratio and PSII antenna size to maximize its photosynthetic performance during light acclimation. Its large PSII antenna consists of many weakly bound LHCIIs, which form effective quenching centers, even at relatively low light. This, together with sensitive photosynthetic control on the level of cytochrome b6f complex (protecting PSI), is the crucial photoprotective mechanism in spruce. High-light acclimation of spruce involves the disruption of PSII macro-organization, reduction of the amount of both PSII and PSI core complexes, synthesis of stress proteins that bind released Chls, and formation of "locked-in" quenching centers from uncoupled LHCIIs. Such response has been previously observed in the evergreen angiosperm Monstera deliciosa exposed to high light. We suggest that, in contrast to annuals, shade-tolerant evergreen land plants have their own strategy to cope with light intensity changes and the hallmark of this strategy is a stable Chl a/b ratio.

• Keywords
• Arabidopsis thaliana, LHCII antenna, Light acclimation, Non-photochemical quenching, Photoprotection, Photosynthetic control, Picea abies, Thylakoid membrane,
• MeSH
• Acclimatization MeSH
• Arabidopsis * metabolism   MeSH
• Chlorophyll A metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Cytochromes b metabolism   MeSH
• Photosystem I Protein Complex metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Cytochrome b6f Complex metabolism   MeSH
• Heat-Shock Proteins metabolism   MeSH
• Picea * metabolism   MeSH
• Light MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll A MeSH
• Chlorophyll MeSH
• Cytochromes b MeSH
• Photosystem I Protein Complex MeSH
• Photosystem II Protein Complex MeSH
• Cytochrome b6f Complex MeSH
• Heat-Shock Proteins MeSH
• Light-Harvesting Protein Complexes MeSH

It is well established that plant thylakoid membranes (TMs), in addition to a bilayer, contain two isotropic lipid phases and an inverted hexagonal (HII) phase. To elucidate the origin of non-bilayer lipid phases, we recorded the 31P-NMR spectra of isolated spinach plastoglobuli and TMs and tested their susceptibilities to lipases and proteases; the structural and functional characteristics of TMs were monitored using biophysical techniques and CN-PAGE. Phospholipase-A1 gradually destroyed all 31P-NMR-detectable lipid phases of isolated TMs, but the weak signal of isolated plastoglobuli was not affected. Parallel with the destabilization of their lamellar phase, TMs lost their impermeability; other effects, mainly on Photosystem-II, lagged behind the destruction of the original phases. Wheat-germ lipase selectively eliminated the isotropic phases but exerted little or no effect on the structural and functional parameters of TMs-indicating that the isotropic phases are located outside the protein-rich regions and might be involved in membrane fusion. Trypsin and Proteinase K selectively suppressed the HII phase-suggesting that a large fraction of TM lipids encapsulate stroma-side proteins or polypeptides. We conclude that-in line with the Dynamic Exchange Model-the non-bilayer lipid phases of TMs are found in subdomains separated from but interconnected with the bilayer accommodating the main components of the photosynthetic machinery.

• Keywords
• 31P-NMR spectroscopy, lipid polymorphism, lipocalins, membrane fusion, membrane models, non-bilayer lipids, plastoglobuli, structural and functional plasticity, thylakoid membrane,
• MeSH
• Lipase metabolism   MeSH
• Lipid Bilayers * metabolism   MeSH
• Magnetic Resonance Spectroscopy MeSH
• Peptide Hydrolases metabolism   MeSH
• Thylakoids * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Lipase MeSH
• Lipid Bilayers * MeSH
• Peptide Hydrolases MeSH

Light quality significantly influences plant metabolism, growth and development. Recently, we have demonstrated that leaves of barley and other plant species grown under monochromatic green light (500-590 nm) accumulated a large pool of chlorophyll a (Chl a) intermediates with incomplete hydrogenation of their phytyl chains. In this work, we studied accumulation of these geranylgeranylated Chls a and b in pigment-protein complexes (PPCs) of Arabidopsis plants acclimated to green light and their structural-functional consequences on the photosynthetic apparatus. We found that geranylgeranylated Chls are present in all major PPCs, although their presence was more pronounced in light-harvesting complex II (LHCII) and less prominent in supercomplexes of photosystem II (PSII). Accumulation of geranylgeranylated Chls hampered the formation of PSII and PSI super- and megacomplexes in the thylakoid membranes as well as their assembly into chiral macrodomains; it also lowered the temperature stability of the PPCs, especially that of LHCII trimers, which led to their monomerization and an anomaly in the photoprotective mechanism of non-photochemical quenching. Role of geranylgeranylated Chls in adverse effects on photosynthetic apparatus of plants acclimated to green light is discussed.

• Keywords
• Arabidopsis thaliana, Chlorophylls, Green light, Structure and function of photosystem II, Thermal stability, Thylakoid membrane,
• MeSH
• Adaptation, Ocular physiology   MeSH
• Arabidopsis metabolism   MeSH
• Chlorophyll metabolism   MeSH
• Photosystem II Protein Complex metabolism   MeSH
• Prenylation MeSH
• Light-Harvesting Protein Complexes metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Chlorophyll MeSH
• Photosystem II Protein Complex MeSH
• Light-Harvesting Protein Complexes MeSH