scholarly journals The effects of galactolipid depletion on the structure of a photosynthetic membrane.

1986 ◽  
Vol 103 (4) ◽  
pp. 1337-1347 ◽  
Author(s):  
J S Jacob ◽  
K R Miller
Keyword(s):  
Fatty Acids ◽  
Photosystem Ii ◽  
Membrane Structure ◽  
Membrane Lipids ◽  
Freeze Fracture ◽  
Membrane System ◽  
Water Soluble ◽  
Membrane Composition ◽  
Higher Plant ◽  
Photosynthetic Membrane

The galactolipids monogalactosyldiglyceride and digalactosyldiglyceride together comprise more than 77% of the photosynthetic membrane lipids of higher plant chloroplasts. We have isolated a lipase from the chloroplasts of runner beans (Phaseolus vulgaris) which is highly specific for these galactolipids. This galactolipase promotes the hydrolysis of monogalactosyldiglyceride and digalactosyldiglyceride, in the process liberating two free fatty acids into the membrane bilayer, leaving the residual galactosyl glyceride group to diffuse into the aqueous bulk phase. Isolated spinach photosynthetic membranes were treated with this enzyme preparation and changes in membrane composition were studied with thin layer chromatography (for lipids), gel electrophoresis (proteins), and freeze-etching (membrane structure). After 30 min of lipolysis, nearly 100% of the galactolipids had been converted into membrane-associated fatty acids and water-soluble galactosyl glycerides. SDS PAGE showed that two proteins, one of which is possibly associated with the reaction center of photosystem II, were removed by the treatment. Despite the minor nature of changes in membrane protein composition, freeze-fracture and freeze-etch studies showed that striking changes in membrane structure had taken place. The large freeze-fracture particle on the E fracture face had disappeared in stacked regions of the membrane system. In addition, a tetrameric particle visible at the inner surface of the membrane had apparently dissociated into individual monomeric particles. The fact that these two structures are so dramatically affected by the loss of galactolipids strongly suggests that these lipids play a crucial role in maintaining their structure. Both structures are believed to be different views of the same transmembrane unit: a membrane-spanning complex associated with photosystem II. Our results are consistent with two possible interpretations: the intramembrane particles may be lipidic in nature, and hence lipolysis causes their disappearance; or galactolipids are necessary for the organization of a complex photosystem II-associated structure which is composed of a number of different molecular species.

Phytotoxic Action of Paraquat on the Photosynthetic Apparatus

1978 ◽  
Vol 33 (9-10) ◽  
pp. 688-694 ◽  
Author(s):  
Peter Böger ◽  
K. J. Kunert
Keyword(s):  
Photosystem Ii ◽  
Redox Reactions ◽  
Photosynthetic Apparatus ◽  
Membrane System ◽  
Culture Conditions ◽  
Terminal Part ◽  
Photosynthetic Membrane ◽  
Redox Chain ◽  
Chlorophyll Bleaching ◽  
Chloroplast Volume

Abstract Treatment of microalgae (Bumilleriopsis) with paraquat (1,1-dimethyl-4,4-dipyridylium dichloride) under culture conditions in the light for 20 or 160 h leads to light-induced oxygen uptake and more or less severe chlorophyll bleaching, which is accompanied by formation of malondial-dehyde. The ratio of chlorophyll to packed chloroplast volume remains about the same as that of the control, presumably indicating destruction of membranes concurrently with pigments. Unre­lated to retardation of growth, degree of bleaching or to the formation of malondialdehyde quite a uniform degree of inactivation (≈ 50%) of partial redox reactions is observed in the region of photosystem II and I except for the terminal part of photosystem I (pigment 700 → NADP+) . The action of paraquat in the cell centers primarily on the photosynthetic membrane system and redox chain.

Compositional analysis of the photosynthetic membrane system of western hemlock chloroplasts

1977 ◽  
Vol 55 (18) ◽  
pp. 2399-2407 ◽  
Author(s):  
David R. DeYoe ◽  
Gregory N. Brown
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Membrane Protein ◽  
Thylakoid Membrane ◽  
Membrane System ◽  
Tsuga Heterophylla ◽  
Western Hemlock ◽  
Gas Liquid Chromatography ◽  
Protein Patterns ◽  
Photosynthetic Membrane

The protein, lipid, and fatty acid composition of the thylakoid membrane system of western hemlock (Tsuga heterophylla (Rafn.) Sarg.) chloroplasts was determined. Linear gradient slab gel electrophoresis of SDS-solubilized membrane protein preparations from the thylakoid system and its photosystem I (D144) and II (D10) subfractions resolved 32 protein bands. Density analysis of electrophoretic patterns accompanied by molecular weight determinations distinguished complex I at 63 kilodaltons and complex II at 23 kilodaltons.Sequential extraction of the thylakoid pellet in acetone - ethyl ether (4:1, v/v) and chloroform–methanol (2:1, v/v) followed by gel filtration on lipophilic Sephadex LH-20 provided two major lipid fractions. Qualitative thin-layer chromatography using lipid standards and colorimetric assays revealed the presence of monogalactosyl diglyceride, digalactosyl diglyceride, sulphoquinovosyl diglyceride, phosphatidyl glycerol, phosphatidyl choline, and phosphatidyl inositol. The concentration of each glycerolipid in micromolars per gram fresh weight of needle tissue was 11.16, 9.90, 6.18, 5.25, 3.16, and 2.32, respectively.The fatty acid contingent of each glycerolipid was determined by gas–liquid chromatography using 15% HI–EFF–IBP on Chromosorb W (100–200 mesh). Trimethyl(α, α, α-trifloro-m-tolyl)ammonium hydroxide was used as the 'on-column' active methylating agent. The following fatty acids were present at detectable concentrations in each of the glycerolipids: palmitic (16:0), palmitoleic (16:1), stearic (18:0), oleic (18:1), linoleic (18:2), linolenic (18:3), and 11-eiconsenoic (20:1). The major fatty acids of the phospholipids were 16:0 and 18:1, while the predominant fatty acids of the glycolipids were 18:3, 18:1, and 16:0.Western hemlock thylakoid membrane protein patterns appeared remarkably similar to those demonstrated in numerous plant and algal systems. On the other hand, thylakoid glycerolipids and their respective fatty acids, while qualitatively similar, revealed significant quantitative differences from values reported for herbaceous species.

Effects of aging on chlorophyll fluorescence and photosystem II electron transport in isolated chloroplasts

1975 ◽  
Vol 53 (23) ◽  
pp. 2842-2845 ◽  
Author(s):  
M. Fragata
Keyword(s):  
Fatty Acids ◽  
Chlorophyll Fluorescence ◽  
Photosystem Ii ◽  
Conformational Changes ◽  
Photochemical Activity ◽  
Photosynthetic Membrane ◽  
Fluorescence Characteristics ◽  
Protein Molecules ◽  
Effects Of Aging ◽  
Isolated Chloroplasts

The correlation between emission of energy and photochemical activity in isolated chloroplasts during aging was investigated. It was shown that aging hinders the intensity of chlorophyll-a fluorescence with a concomitant decrease of the photosystem II activity. In view of the parallelism between the action of exogenous fatty acids, especially C18-unsaturated acids, and the effects of aging, it is suggested that the thylakoid transformation during aging could result partly from conformational changes of the membrane polypeptides due to the presence of free fatty acids in the neighborhood of the protein molecules. It is possible that such a mechanism of fatty acid action may alter the fluorescence characteristics of chlorophyll as well as the tunneling of electrons in the photosynthetic membrane.

scholarly journals Specific Incorporation of Polyunsaturated Fatty Acids into the sn-2 Position of Phosphatidylglycerol Accelerates Photodamage to Photosystem II under Strong Light

2021 ◽  
Vol 22 (19) ◽  
pp. 10432
Author(s):  
Haruhiko Jimbo ◽  
Koki Yuasa ◽  
Kensuke Takagi ◽  
Takashi Hirashima ◽  
Sumie Keta ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Photosystem Ii ◽  
Polyunsaturated Fatty Acids ◽  
Membrane Lipids ◽  
Monounsaturated Fatty Acids ◽  
Oxygen Evolving Complex ◽  
Strong Light ◽  
Photosynthetic Organisms ◽  
Oxygen Evolving ◽  
Synechocystis Sp

Free fatty acids (FFAs) are generated by the reaction of lipases with membrane lipids. Generated polyunsaturated fatty acids (PUFAs) containing more than two double bonds have toxic effects in photosynthetic organisms. In the present study, we examined the effect of exogenous FFAs in the growth medium on the activity of photosystem II (PSII) under strong light in the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). PUFAs but not monounsaturated fatty acids accelerated the rate of photodamage to PSII by inactivating electron transfer at the oxygen-evolving complex. Moreover, supplemented PUFAs were specifically incorporated into the sn-2 position of phosphatidylglycerol (PG), which usually contains C16 fatty acids at the sn-2 position in Synechocystis cells. The disruption of the gene for an acyl-ACP synthetase reduced the effect of PUFAs on the photoinhibition of PSII. Thus, the specific incorporation of PUFAs into PG molecules requires acyl-ACP synthetase and leads to an unstable PSII, thereby accelerating photodamage to PSII. Our results are a breakthrough into elucidating the molecular mechanism of the toxicity of PUFAs to photosynthetic organisms.

scholarly journals Studies on the mechanism of polyethylene glycol-mediated cell fusion using fluorescent membrane and cytoplasmic probes.

1983 ◽  
Vol 96 (1) ◽  
pp. 151-159 ◽  
Author(s):  
J W Wojcieszyn ◽  
R A Schlegel ◽  
K Lumley-Sapanski ◽  
K A Jacobson
Keyword(s):  
Polyethylene Glycol ◽  
Cell Fusion ◽  
Cultured Cells ◽  
Membrane Lipids ◽  
Freeze Fracture ◽  
Water Soluble ◽  
Erythrocyte Membranes ◽  
Adjacent Cell ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron

The mechanism by which polyethylene glycol (PEG) mediates cell fusion has been studied by examining the movements of membrane lipids and proteins, as well as cytoplasmic markers, from erythrocytes to monolayers of cultured cells to which they have been fused. Fluorescence and freeze-fracture electron microscopy and fluorescence recovery after photobleaching have yielded the following results: (a) In the presence of both fusogenic and nonfusogenic PEG membranes are brought together at closely apposed contact regions. (b) Fluorescent lipid probes quickly spread from the membranes of erythrocytes to cultured cells in the presence of both fusogenic and nonfusogenic PEG. (c) Proteins of the erythrocyte membranes were never observed to diffuse into the cultured cell membrane. (d) Water-soluble proteins did not diffuse from the erythrocyte interior into the target cell cytoplasm until the PEG was removed. These data suggest that the coordinate action of two distinct components is necessary for fusion as mediated by PEG. Presumably, the polymer itself promotes close apposition of the adjacent cell membranes but the fusion stimulus is provided by the additives contained in commercial PEG.

Warm and freeze-fracture of cotton seed radicles

1987 ◽  
Vol 45 ◽  
pp. 984-985
Author(s):  
E. L. Vigil ◽  
E. F. Erbe
Keyword(s):  
Thin Film ◽  
Water Vapor ◽  
Fracture Surface ◽  
Membrane Structure ◽  
Room Temperature ◽  
Freeze Fracture ◽  
Longitudinal Axis ◽  
Fracture Plane ◽  
Cotton Seeds ◽  
Condensed Water

In cotton seeds the radicle has 12% moisture content which makes it possible to prepare freeze-fracture replicas without fixation or cryoprotection. For this study we have examined replicas of unfixed radicle tissue fractured at room temperature to obtain data on organelle and membrane structure.Excised radicles from seeds of cotton (Gossyplum hirsutum L. M-8) were fractured at room temperature along the longitudinal axis. The fracture was initiated by spliting the basal end of the excised radicle with a razor. This procedure produced a fracture through the tissue along an unknown fracture plane. The warm fractured radicle halves were placed on a thin film of 100% glycerol on a flat brass cap with fracture surface up. The cap was rapidly plunged into liquid nitrogen and transferred to a freeze- etch unit. The sample was etched for 3 min at -95°C to remove any condensed water vapor and then cooled to -150°C for platinum/carbon evaporation.

scholarly journals Effects of exogenous silicon on maize seed germination and seedling growth

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yankun Sun ◽  
Jiaqi Xu ◽  
Xiangyang Miao ◽  
Xuesong Lin ◽  
Wanzhen Liu ◽  
...  
Keyword(s):  
Seed Germination ◽  
Seedling Growth ◽  
Crop Yields ◽  
Dry Weight ◽  
Membrane System ◽  
Water Soluble ◽  
Current Status ◽  
Antioxidant Enzyme Activities ◽  
Chlorophyll Contents ◽  
Antioxidant Defence System

AbstractAs the global population continues to increase, global food production needs to double by 2050 to meet the demand. Given the current status of the not expansion of cultivated land area, agronomic seedlings are complete, well-formed and strong, which is the basis of high crop yields. The aim of this experiment was to study the effects of seed germination and seedling growth in response to silicon (from water-soluble Si fertilizer). The effects of Si on the maize germination, seedling growth, chlorophyll contents, osmoprotectant contents, antioxidant enzyme activities, non-enzymatic antioxidant contents and stomatal characteristics were studied by soaking Xianyu 335 in solutions of different concentrations of Si (0, 5, 10, 15, 20, and 25 g·L−1). In this study, Si treatments significantly increased the seed germination and per-plant dry weight of seedlings (P < 0.05), and the optimal concentration was 15 g·L−1. As a result of the Si treatment of the seeds, the chlorophyll content, osmotic material accumulation and antioxidant defence system activity increased, reducing membrane system damage, reactive oxygen species contents, and stomatal aperture. The results suggested that 15 g·L−1 Si significantly stimulated seed germination and promoted the growth of maize seedlings, laying a solid foundation for subsequent maize growth.

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