thylakoid pattern
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Since the publication of the fluid-mosaic membrane theory by Singer and Nicolson in 1972 generations of scientists have adopted this fascinating concept for all biological membranes. Assuming the membrane as a fluid implies that the components embedded in the lipid bilayer can freely diffuse like swimmers in a water body. During the detailed biochemical analysis of the thylakoid protein components of chloroplasts from higher plants and algae, in the '80 s and '90 s it became clear that photosynthetic membranes are not homogeneous either in the vertical or the lateral directions. The lateral heterogeneity became obvious by the differentiation of grana and stroma thylakoids, but also the margins have been identified with a highly specific protein pattern. Further refinement of the fluid mosaic model was needed to take into account the presence of non-bilayer lipids, which are the most abundant lipids in all energy-converting membranes, and the polymorphism of lipid phases, which has also been documented in thylakoid membranes. These observations lead to the question, how mobile the components are in the lipid phase and how this ordering is made and maintained and how these features might be correlated with the non-bilayer propensity of the membrane lipids. Assuming instead of free diffusion, a "controlled neighborhood" replaced the model of fluidity by the model of a "mixed crystal structure". In this review we describe why basic photosynthetic regulation mechanisms depend on arrays of crystal-like lipid-protein macro-assemblies. The mechanisms which define the ordering in macrodomains are still not completely clear, but some recent experiments give an idea how this fascinating order is produced, adopted and maintained. We use the operation of the xanthophyll cycle as a rather well understood model challenging and complementing the standard Singer-Nicolson model via assigning special roles to non-bilayer lipids and non-lamellar lipid phases in the structure and function of thylakoid membranes.
The function of selenium in an organism is mediated mostly by selenoproteins including glutathione peroxidase. Glutathione peroxidase is a potent anti-oxidative enzyme, scavenging a variety of peroxides. The green alga Scenedesmus quadricauda was used to investigate the relationship between the toxicity of selenium and the glutathione peroxidase activity. Selenium resistant strains SeIV and SeVI were synchronized and grown in high concentrations of Se (selenite or selenate). As a measure of selenium toxicity the EC(50) values were determined. During growth of the untreated wild type, glutathione peroxidase activity increased slightly and then declined gradually until the end of the cell cycle. A similar pattern was observed in untreated resistant strains and when resistant strains were grown in the presence of selenium in the oxidation state to which they were resistant. In the wild type cultivated with 50 mg Se L(-1) (selenite or selenate), activity increased to a high level and slowly declined until the end of the cell cycle. Similarly, activity increased in strains SeIV and SeVI when grown in the presence of selenium in the oxidation state to which they were not resistant. We followed the effect of selenium on the ultrastructure of S. quadricauda. After exposure to selenite, the chloroplast membranes of wild type were reorganized into thick bundles of thylakoids and the stroma became granulose. When selenate was added, the chloroplast of wild type had a fingerprint-like appearance, the stroma became less dense and starch production increased. In selenium resistant strains, when treated with the selenium form to which they were resistant, the chloroplast was affected, but not to such an extent as in the wild type. The activity of glutathione peroxidase in Scenedesmus was affected by selenium in an oxidation state-dependent manner. The most apparent effects of selenium on the ultrastructure involved impairment of the chloroplast and the overproduction of starch.
- MeSH
- buněčný cyklus účinky léků fyziologie MeSH
- chloroplasty účinky léků metabolismus ultrastruktura MeSH
- fyziologický stres MeSH
- geneticky modifikované rostliny MeSH
- glutathionperoxidasa metabolismus MeSH
- kultivační techniky MeSH
- Scenedesmus cytologie účinky léků enzymologie fyziologie MeSH
- selen aplikace a dávkování analýza toxicita MeSH
- seleničitan sodný aplikace a dávkování toxicita MeSH
- sloučeniny selenu aplikace a dávkování toxicita MeSH
- testy toxicity MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
... Fold into a Conformation of Lowest Energy 114 -- The a Helix and the ß Sheet Are Common Folding Patterns ... ... Cine-Wide Alterations in Chromatin Structure Can Be r merted ísk - ac Mechanisms Ensure That Stable Patterns ... ... Summary -- CHLOROPLASTS AND PHOTOSYNTHESIS -- Chloroplasts Resemble Mitochondria But Have a Separate Thylakoid ... ... Sugars -- Sugars Generated by Carbon Fixation Can Be Stored as Starch or Consumed to Produce ATP The Thylakoid ... ... Energy or Electrons -- A Photosystem Consists of an Antenna Complex and a Reaction Center -- The Thylakoid ...
Sixth edition xxxiv, 1430 stran v různém stránkování : ilustrace (převážně barevné) ; 29 cm
- Konspekt
- Biochemie. Molekulární biologie. Biofyzika
- NLK Obory
- molekulární biologie, molekulární medicína
- NLK Publikační typ
- učebnice vysokých škol
... Metaphase Are Species-Specific 257 -- During Metaphase, Chromosomes Can Be Distinguished by Banding Patterns ... ... INTO -- MEMBRANES AND ORGANELLES 533 -- 12.4 -- Photosynthesis and Light-Absorbing Pigments 511 -- Thylakoid ... ... Proteins Is Similar to Import of Mitochondrial Matrix Proteins 565 -- Proteins Are Targeted to Thylakoids ... ... Good Thing: The X Chromosome Is -- Regulated by Dosage Compensation 958 -- I Cell Diversity and Patterning ... ... Embryo\'s -- Anterior and Posterior 971 -- Translation Inhibitors Reinforce Anterior-Posterior -- Patterning ...
6th ed. xxxvii, 1150 s. : il., tab. ; 29 cm
- MeSH
- biologie buňky MeSH
- molekulární biologie MeSH
- Publikační typ
- monografie MeSH
- Konspekt
- Biochemie. Molekulární biologie. Biofyzika
- NLK Obory
- biologie
- cytologie, klinická cytologie
... Choroplasts 528 -- —j XXX l CONTENTS -- 19.1.1 The Primary Events of Photosynthesis Take -- Place in Thylakoid ... ... Ferredoxin-NADP+ Reductase Converts -- NADP+ into NADPH 539 -- 19.4 A Proton Gradient Across the Thylakoid ... ... Transcription by -- Perturbing Chromatin Structure 878 -- 31.2.5 The Modification of DNA Can Alter Patterns ...
5th ed. xvii, 974 s. : il., tab., grafy ; 32 cm
