In Part I, by using 31P-NMR spectroscopy, we have shown that isolated granum and stroma thylakoid membranes (TMs), in addition to the bilayer, display two isotropic phases and an inverted hexagonal (HII) phase; saturation transfer experiments and selective effects of lipase and thermal treatments have shown that these phases arise from distinct, yet interconnectable structural entities. To obtain information on the functional roles and origin of the different lipid phases, here we performed spectroscopic measurements and inspected the ultrastructure of these TM fragments. Circular dichroism, 77 K fluorescence emission spectroscopy, and variable chlorophyll-a fluorescence measurements revealed only minor lipase- or thermally induced changes in the photosynthetic machinery. Electrochromic absorbance transients showed that the TM fragments were re-sealed, and the vesicles largely retained their impermeabilities after lipase treatments-in line with the low susceptibility of the bilayer against the same treatment, as reflected by our 31P-NMR spectroscopy. Signatures of HII-phase could not be discerned with small-angle X-ray scattering-but traces of HII structures, without long-range order, were found by freeze-fracture electron microscopy (FF-EM) and cryo-electron tomography (CET). EM and CET images also revealed the presence of small vesicles and fusion of membrane particles, which might account for one of the isotropic phases. Interaction of VDE (violaxanthin de-epoxidase, detected by Western blot technique in both membrane fragments) with TM lipids might account for the other isotropic phase. In general, non-bilayer lipids are proposed to play role in the self-assembly of the highly organized yet dynamic TM network in chloroplasts.
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.
The role of non-bilayer lipids and non-lamellar lipid phases in biological membranes is an enigmatic problem of membrane biology. Non-bilayer lipids are present in large amounts in all membranes; in energy-converting membranes they constitute about half of their total lipid content-yet their functional state is a bilayer. In vitro experiments revealed that the functioning of the water-soluble violaxanthin de-epoxidase (VDE) enzyme of plant thylakoids requires the presence of a non-bilayer lipid phase. 31P-NMR spectroscopy has provided evidence on lipid polymorphism in functional thylakoid membranes. Here we reveal reversible pH- and temperature-dependent changes of the lipid-phase behaviour, particularly the flexibility of isotropic non-lamellar phases, of isolated spinach thylakoids. These reorganizations are accompanied by changes in the permeability and thermodynamic parameters of the membranes and appear to control the activity of VDE and the photoprotective mechanism of non-photochemical quenching of chlorophyll-a fluorescence. The data demonstrate, for the first time in native membranes, the modulation of the activity of a water-soluble enzyme by a non-bilayer lipid phase.
- MeSH
- diferenciální skenovací kalorimetrie MeSH
- epoxidové sloučeniny metabolismus MeSH
- kinetika MeSH
- koncentrace vodíkových iontů MeSH
- lipidové dvojvrstvy chemie MeSH
- lipidy chemie MeSH
- magnetická rezonanční spektroskopie MeSH
- oxidoreduktasy metabolismus MeSH
- rozpustnost MeSH
- Spinacia oleracea metabolismus MeSH
- světlo MeSH
- teplota MeSH
- tylakoidy chemie MeSH
- voda chemie MeSH
- xanthofyly metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
BACKGROUND AND AIMS: Detection of oligoclonal IgG (o-IgG) in the cerebrospinal fluid (CSF) not found in serum is the principal laboratory test to support a diagnosis of multiple sclerosis. The aim of this study was to compare chemiluminescent and chromogenic detection of oligoclonal immunoglobulins in the cerebrospinal fluid and serum after their separation by means of isoelectric focusing followed by immunoblotting. METHODS: A set of experiments was designed to detect oligoclonal immunoglobulins by means of alkaline phosphatase BCIP/NBT substrate and chemiluminescent peroxidase substrate. RESULTS: Based on visual evaluation of signals, chemiluminescent detection requires about a 4 times lower amount of applied protein than very sensitive BCIP/NBT chromogenic detection. Very good correlation between methods has been shown for oligoclonal IgG. Antigen-specific oligoclonal IgG could be demonstrated by both methods although the pattern was clearer using chemiluminescence. In one patient, oligoclonal IgD bands barely visible by BCIP/NBT were convincingly demonstrated by chemiluminescence. CONCLUSION: Chemiluminescent detection is a feasible option for oligoclonal immunoglobulin detection and could be used in cases when the sensitivity needs to be improved. Further studies and method optimisation are warranted.
Recently, we have found that thermal stability of photosystem II (PSII) photochemistry in spruce needles is higher than in other plants (barley, beech) cultivated under the same temperatures. In this work, temperature dependences of various characteristics of PSII organization were studied in order to obtain complex information on the thermal stability of PSII function and organization in spruce. Temperature dependency of circular dichroism spectra revealed by about 6 °C higher thermal stability of macrodomain organization in spruce thylakoid membranes in comparison with Arabidopsis and barley ones; however, thermal disintegration of light-harvesting complex of PSII did not significantly differ among the species studied. These results thus indicate that thermal stability of PSII macro-organization in spruce thylakoid membranes is enhanced to a similar extent as thermal stability of PSII photochemistry. Clear-native polyacrylamide gel electrophoresis of preheated thylakoids demonstrated that among the separated pigment-protein complexes, only PSII supercomplexes (SCs) revealed considerably higher thermal stability in spruce thylakoids as compared to Arabidopsis and barley ones. Hence we suggest that higher thermal stability of PSII macro-organization of spruce is influenced by the maintenance of PSII SCs in the thylakoid membrane. In addition, we discuss possible effects of different PSII organizations and lipid compositions on the thermal stability of spruce thylakoid membranes.
- MeSH
- Arabidopsis cytologie fyziologie MeSH
- chlorofyl fyziologie MeSH
- cirkulární dichroismus MeSH
- elektroforéza v polyakrylamidovém gelu MeSH
- fluorescence MeSH
- fotosystém II - proteinový komplex fyziologie MeSH
- ječmen (rod) cytologie fyziologie MeSH
- smrk cytologie fyziologie MeSH
- tylakoidy fyziologie MeSH
- vysoká teplota MeSH
- Publikační typ
- časopisecké články MeSH
- srovnávací studie MeSH
