L. Staehelin - Academia.edu (original) (raw)
Papers by L. Staehelin
Plant Signaling & Behavior, 2009
Plant Physiology, 2008
Modern architecture is guided by the axiom ''form follows function,'' which emphasizes the need f... more Modern architecture is guided by the axiom ''form follows function,'' which emphasizes the need for the shape of a building or an object to reflect its intended function or purpose. Biologists tend to prefer the phrase ''form begets function,'' because in living organisms, form not only reflects on function but also defines many functional attributes. This relationship between biological structure and function explains why one of the central goals of 21st century cell biologists is to provide a seamless link of structural understanding between the macroscopic level of tissue organization to the molecular and even atomic level organization of the building blocks of cells and tissues. In turn, this structural knowledge provides architectural constraints for developing testable hypotheses for how macromolecular complexes, organelles, cells, and organs operate on a functional level. The goal of this Update is to summarize new information on the three-dimensional (3D) architecture of the membrane systems of the secretory pathway of plant cells produced by dual-axis electron tomography of cells preserved by high-pressure freezing/freeze-substitution techniques. These studies have redefined our understanding of the nanoscale organization of the membranes of endoplasmic reticulum (ER) export sites, Golgi stacks, trans-Golgi network (TGN) cisternae, and associated vesicles and scaffolds, and by doing so have led to many new insights into the functional organization of these membrane systems. In addition, these studies have created a bridge between live cell imaging by confocal microscopy on one hand and biochemical and molecular investigations on the other.
Plant Physiology, 1985
ABSTRACr We have used the nonionic detergent octyl-O-D-glucopyranoside in combination with sodium... more ABSTRACr We have used the nonionic detergent octyl-O-D-glucopyranoside in combination with sodium dodecyl sulfate to isolate two novel Photosystem I (PSI) complexes from spinach (Spinacea oleracea L.) thylakoid membranes. These complexes have been characterized as to their spectral properties, content of PSI reaction center chlorophyll P7-, and protein composition. PSI-B, purified from solubilized membranes by sucrose density gradient centrifugation, is a putative native PSI complex. PSI-B contains four polypeptides between 21 and 25 kilodaltons in addition to the components of the PSI antenna complex (LHCI), three of these polypeptides have not previously been associated with PSI. A second complex, CPI*, is purified from octyl glucoside/sodium dodecyl sulfate solubilized thylakoids by two cycles of preparative gel electrophoresis under mildly denaturing conditions. Electrophoresis under these conditions releases a discrete set of polypeptides from PSI producing a complex composed only of the PSI reaction center and the LHCI antenna. In addition, the PSI reaction center complex CPI isolated from preparative gels and PSI-B were reconstituted into lecithin liposomes for structural analysis using freeze-fracture electron microscopy. The results suggest that the native PSI complex produces 12to 13-nanometer particles, while the PSI reaction center, depleted of LHCI and peripheral proteins, produces particles with an average diameter of 10 nanometers. The technique used to isolate PSI from higher plant thylakoids usually involves detergent solubilization of the membranes followed by separation ofthe photosynthetic components by either: (a) sucrose density gradient centrifugation and/or ion-exchange chromatography (1, 4, 20, 25, 28, 32, 35); or (b) electrophoresis under mildly denaturing conditions (1, 6, 7, 18, 23, 34). Based on peptide composition and Chl/P7002 ratios, it is possible to classify the different PSI preparations into several levels of structural complexity. PSI particles produced by nonelectrophoretic methods are usually isolated in one of two forms, best represented by the PSI
Current Research in Photosynthesis, 1990
The complexity of the thylakoid membrane frequently necessitates its separation into component pa... more The complexity of the thylakoid membrane frequently necessitates its separation into component parts before meaningful analysis may be carried out. Thylakoid fractionation, typically via disruption of the bilayer with detergents, and subsequent manipulations required for various analytical techniques, always raises the question of the extent to which the solubilized experimental material is representative of the in vivo state. We report here on the application of a new native green gel system to five higher plant species. This system resolves as many as eighteen chlorophyll-protein complexes with very little release of free pigment and with a degree of preservation of subunit-subunit interactions that has not been obtainable with previous systems, suggesting that this system yields a more accurate picture of the native condition of the membrane. The system was originallydeveloped for use with Chlamydomonas thylakoids, from which up to twenty chlorophyll-protein complexes may be resolved (Allen and Staehelin, these Proceedings).
Developmental Biology, 1974
Developing muscle masses from hind limbs of lS-day fetal rats were freeze-cleaved, platinum and c... more Developing muscle masses from hind limbs of lS-day fetal rats were freeze-cleaved, platinum and carbon replicated, and examined electron microscopically. Gap junctions were observed linking cell pairs clearly identified as myogenic by the presence of easily recognized and characteristic arrays of cross or longitudinally fractured myofibrils. Occasionally gap junctions were also observed between identified nonmyogenic cells, but none were observed between myogenic-nonmyogenic cell pairs. Because the recently formed conjoint myogenic cells were already encapsulated by developing basal laminae and normally would have fused to form discrete myofibers, we suggest that this report provides additional evidence that gap junctions normally form immediately before and thus perhaps mediate the initial events of myogenic cell fusion in uiuo as well as in uitro.
Molecular biology of the cell, Jun 1, 2016
The preprophase band (PPB) is a cytokinetic apparatus that determines the site of cell division i... more The preprophase band (PPB) is a cytokinetic apparatus that determines the site of cell division in plants. It originates as a broad band of microtubules (MTs) in G2 and narrows to demarcate the future division site during late prophase. Studies with fluorescent probes have shown that PPBs contain F-actin during early stages of their development but become actin depleted in late prophase. Although this suggests that actins contribute to the early stages of PPB formation, how actins contribute to PPB-MT organization remains unsolved. To address this question, we used electron tomography to investigate the spatial relationship between microfilaments (MFs) and MTs at different stages of PPB assembly in onion cotyledon epidermal cells. We demonstrate that the PPB actins observed by fluorescence microscopy correspond to short, single MFs. A majority of the MFs are bound to MTs, with a subset forming MT-MF-MT bridging structures. During the later stages of PPB assembly, the MF-mediated lin...
Experimental Cell Research, 1974
Proceedings of the National Academy of Sciences, 1996
We have expressed a fusion protein formed between the avian infectious bronchitis virus M protein... more We have expressed a fusion protein formed between the avian infectious bronchitis virus M protein and the bacterial enzyme beta-glucuronidase in transgenic tobacco cells. Electron microscope images of such cells demonstrate that overexpression of this fusion protein gives rise to a type of endoplasmic reticulum membrane domain in which adjacent membranes become zippered together apparently as a consequence of the oligomerizing action of beta-glucuronidase. These zippered (Z-) membranes lack markers of the endoplasmic reticulum (NADH cytochrome c reductase and ribosomes) and accumulate in the cells in the form of multilayered scroll-like structures (up to 2 micrometers in diameter; 20-50 per cell) without affecting plant growth. The discovery of Z-membranes has broad implications for biology and biotechnology in that they provide a means for accumulating large quantities of recombinant membrane proteins within discrete domains of native membranes.
The Journal of Cell Biology, 1980
A highly purified chlorophyll a/b light-harvesting complex (chl a/b LHC; chl a/b ratio 1.2) was o... more A highly purified chlorophyll a/b light-harvesting complex (chl a/b LHC; chl a/b ratio 1.2) was obtained from Triton-solubilized chloroplast membranes of pea and barley according to the method of Burke et al. (1978, Arch. Biochem. Biophys. 187: 252--263). Gel electrophoresis of the cation-precipitated chl a/b LHC from peas reveals the presence of four polypeptides in the 23- to 28-kdalton size range. Three of these peptides appear to be identical to those derived from re-electrophoresed CPII and CPII* bands. In freeze-fracture replicas, the cation-precipitated chl a/b LHC appears as a semicrystalline aggregate of membranous sheets containing closely spaced granules. Upon removal of the cations by dialysis, the aggregates break up into their constituent membranous sheets without changing their granular substructure. These membranous sheets can be resolubilized in 1.5% Triton X-100, and the chl a/b LHC particles then reconstituted into soybean lecithin liposomes. Freeze-fracture micro...
PLANT PHYSIOLOGY, 1988
Characterization of the functional organization of the photochemical apparatus in the light sensi... more Characterization of the functional organization of the photochemical apparatus in the light sensitive chlorophyll b-deficient oil yellow-yellow green (OY-YG) mutant of maize (Zea mays) is presented. Spectrophotometric and kinetic analysis revealed substantially lower amounts of the light harvesting complex of photosystem II (LHCII-peripheral) in high light-grown OY-YG thylakoids. However, accumulation of a tightly bound LHCII appears unaffected by the lesion. Changes in photosystem (PS) stoichiometry include lower amounts of PSII with characteristic fast kinetics (PSIIa) and a substantial accumulation of PSII centers with characteristic slow kinetics (PSII,,) in the thylakoid membrane of the OY-YG mutant. Thus, PSII5, is the dominant photosystem in the mutant chloroplasts. In contrast to wild type, roughly 80% of the mutant PSII,, centers are functionally coupled to the plastoquinone pool and are probably localized in the appressed regions of the thylakoid membrane. These centers, designated PSII,J-QB-reducing (QB being the secondary electron quinone acceptor of PSII), are clearly distinct from the typical PSIIJ,-QB-nonreducing centers found in the stroma lamellae of wild-type chloroplasts. It is concluded that the observed changes in the stoichiometry of electrontransport complexes reflect the existence of a regulatory mechanism for the adjustment of photosystem stoichiometry in chloroplasts designed to correct any imbalance in light absorption by the two photosystems.
The Journal of Cell Biology, 1983
A chlorophyll-protein complex of chloroplast membranes, which simultaneously serves as light-harv... more A chlorophyll-protein complex of chloroplast membranes, which simultaneously serves as light-harvesting antenna and membrane adhesion factor, undergoes reversible, lateral diffusion between appressed and nonappressed membrane regions under the control of a protein kinase. The phosphorylation-dependent migration process regulates the amount of light energy that is delivered to the reaction centers of photosystems I and II (PS I and PS II), and thereby regulates their rate of turnover. This regulatory mechanism provides a rationale for the finding that the two photosystems are physically separated in chloroplast membranes (PS II in appressed, grana membranes, and PS I in nonappressed, stroma membranes). The feedback system involves the following steps: a membrane-bound kinase senses the rate of PS II vs. PS I turnover via the oxidation-reduction state of the plastoquinone pool, which shuttles electrons from PS II via cytochrome f to PS I. If activated, the kinase adds negative charge ...
Thelight-sensitive chlorophyll b(Chlb)-deficient oil yellow-yellow green (OY-YG)mutantofmaize(Zea... more Thelight-sensitive chlorophyll b(Chlb)-deficient oil yellow-yellow green (OY-YG)mutantofmaize(Zeamays)grownunderconditions ofhigh light exhibits differential reductions intheaccumulation ofthethree major Chlb-containing antenna complexes andcharacteristic changes inthy- lakoid architecture. Whenobserved byfreeze-fracture electron micro- scopy, themostnotable changes intheOY-YGthylakoid structure are: (a)a majorreduction inthenumberof8nanometer particles ofthe protoplasmic fracture face ofstacked membrane regions (PFs) paralleled bya60%reduction inthechlorophyll-proteins (CP)associated withthe peripheral light harvesting complex (LHCII) forphotosystem II(PSII) andwhichgive rise totheLHCIIoligomer/monomer (CPH*/CPII) bands onmildly dissociated greengels; (b)asizable decrease intheproportion of11to13nanometer particles oftheprotoplasmic fracture faceofun- stacked membraneregions (PFu) thatparallels theloss oflight harvesting complex I(LHCI) antennae fromphotosystem I(PSI) centers anda4...
The Plant cell, Jan 7, 2018
Biogenesis of the complex 3D architecture of plant thylakoids remains an unsolved problem. Here, ... more Biogenesis of the complex 3D architecture of plant thylakoids remains an unsolved problem. Here, we analyzed this process in chloroplasts of germinating Arabidopsis thaliana cotyledons using 3D electron microscopy and gene expression analyses of chloroplast proteins. Our study identified a linear developmental sequence with five assembly stages: tubulo-vesicular pro-thylakoids (24 HAI; hours after imbibition); sheet-like pre-granal thylakoids that develop from the pro-thylakoids (36 HAI); proliferation of pro-grana stacks with wide tubular connections to the originating pre-grana thylakoids (60 HAI); structural differentiation of pro-grana stacks and expanded stroma thylakoids (84 HAI); conversion of the pro-grana stacks into mature grana stacks (120 HAI). Development of the planar pre-granal thylakoids and the pro-grana membrane stacks coincides with the appearance of thylakoid-bound polysomes and photosystem II (PSII) complex subunits at 36 HAI. ATP synthase, cytochrome b6f and li...
Additional file 1: Figure S1. Gallery of tomographic reconstructions of Golgi stacks for each typ... more Additional file 1: Figure S1. Gallery of tomographic reconstructions of Golgi stacks for each type of tomographic sample studied (control, and 1, 4 and 6Â days BSA-induced). Each horizontal line represents a Golgi stack with cis cisternae colored orange and green, medial cisternae blue, pink and yellow, and trans cisternae colored purple and red. Within each group, the Golgi shown are from different cells. These data illustrate the inherent variability in structure of the Golgi cisternae. Bar 0.2Â Âľm.
Chris Somerville Carnegie Institution and Department of Biological Sciences, Stanford University ... more Chris Somerville Carnegie Institution and Department of Biological Sciences, Stanford University During the past 25 years, plant biologists have developed Arabidopsis into a very powerful tool for basic research. However, total federal funding for plant biology is less than 1% of the NIH budget. This ridiculous situation is not improved by having special interest groups within the plant biology community fighting for crumbs. I have long-believed that the heart of the problem is that plant biology is viewed as agriculture. Legislators view the big problem in agriculture as overproduction and do not see the point of further investments in basic research that might cause more overproduction. Additionally colleagues who work on crops species are likely to be first at the federal trough when the arguments are based on improving agriculture. I suggest that a more relevant social context for basic research in plant biology is energy. Although there is enough fossil fuel to meet our energy ...
Journal of Biological Research-Thessaloniki
Background: The insect-trapping leaves of Dionaea muscipula provide a model for studying the secr... more Background: The insect-trapping leaves of Dionaea muscipula provide a model for studying the secretory pathway of an inducible plant secretory system. The leaf glands were induced with bovine serum albumin to secrete proteases that were characterized via zymogram activity gels over a 6-day period. The accompanying morphological changes of the endoplasmic reticulum (ER) and Golgi were analyzed using 3D electron tomography of glands preserved by highpressure freezing/freeze substitution methods. Results: Secretion of multiple cysteine and aspartic proteases occurred biphasically. The majority of the Golgi was organized in clusters consisting of 3-6 stacks surrounded by a cage-like system of ER cisternae. In these clusters, all Golgi stacks were oriented with their cis-most C1 cisterna facing an ER export site. The C1 Golgi cisternae varied in size and shape consistent with the hypothesis that they form de novo. Following induction, the number of ER-bound polysomes doubled, but no increase in COPII vesicles was observed. Golgi changes included a reduction in the number of cisternae per stack and a doubling of cisternal volume without increased surface area. Polysaccharide molecules that form the sticky slime cause swelling of the trans and trans Golgi network (TGN) cisternae. Peeling of the trans-most cisternae gives rise to free TGN cisternae. One day after gland stimulation, the free TGNs were frequently associated with loose groups of oriented actin-like filaments which were not seen in any other samples. Conclusions: These findings suggest that the secretory apparatus of resting gland cells is "overbuilt" to enable the cells to rapidly up-regulate lytic enzyme production and secretion in response to prey trapping.
The use of registered names, trademarks, etc. in this publication does not imply, even in the abs... more The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.
Plant Signaling & Behavior, 2009
Plant Physiology, 2008
Modern architecture is guided by the axiom ''form follows function,'' which emphasizes the need f... more Modern architecture is guided by the axiom ''form follows function,'' which emphasizes the need for the shape of a building or an object to reflect its intended function or purpose. Biologists tend to prefer the phrase ''form begets function,'' because in living organisms, form not only reflects on function but also defines many functional attributes. This relationship between biological structure and function explains why one of the central goals of 21st century cell biologists is to provide a seamless link of structural understanding between the macroscopic level of tissue organization to the molecular and even atomic level organization of the building blocks of cells and tissues. In turn, this structural knowledge provides architectural constraints for developing testable hypotheses for how macromolecular complexes, organelles, cells, and organs operate on a functional level. The goal of this Update is to summarize new information on the three-dimensional (3D) architecture of the membrane systems of the secretory pathway of plant cells produced by dual-axis electron tomography of cells preserved by high-pressure freezing/freeze-substitution techniques. These studies have redefined our understanding of the nanoscale organization of the membranes of endoplasmic reticulum (ER) export sites, Golgi stacks, trans-Golgi network (TGN) cisternae, and associated vesicles and scaffolds, and by doing so have led to many new insights into the functional organization of these membrane systems. In addition, these studies have created a bridge between live cell imaging by confocal microscopy on one hand and biochemical and molecular investigations on the other.
Plant Physiology, 1985
ABSTRACr We have used the nonionic detergent octyl-O-D-glucopyranoside in combination with sodium... more ABSTRACr We have used the nonionic detergent octyl-O-D-glucopyranoside in combination with sodium dodecyl sulfate to isolate two novel Photosystem I (PSI) complexes from spinach (Spinacea oleracea L.) thylakoid membranes. These complexes have been characterized as to their spectral properties, content of PSI reaction center chlorophyll P7-, and protein composition. PSI-B, purified from solubilized membranes by sucrose density gradient centrifugation, is a putative native PSI complex. PSI-B contains four polypeptides between 21 and 25 kilodaltons in addition to the components of the PSI antenna complex (LHCI), three of these polypeptides have not previously been associated with PSI. A second complex, CPI*, is purified from octyl glucoside/sodium dodecyl sulfate solubilized thylakoids by two cycles of preparative gel electrophoresis under mildly denaturing conditions. Electrophoresis under these conditions releases a discrete set of polypeptides from PSI producing a complex composed only of the PSI reaction center and the LHCI antenna. In addition, the PSI reaction center complex CPI isolated from preparative gels and PSI-B were reconstituted into lecithin liposomes for structural analysis using freeze-fracture electron microscopy. The results suggest that the native PSI complex produces 12to 13-nanometer particles, while the PSI reaction center, depleted of LHCI and peripheral proteins, produces particles with an average diameter of 10 nanometers. The technique used to isolate PSI from higher plant thylakoids usually involves detergent solubilization of the membranes followed by separation ofthe photosynthetic components by either: (a) sucrose density gradient centrifugation and/or ion-exchange chromatography (1, 4, 20, 25, 28, 32, 35); or (b) electrophoresis under mildly denaturing conditions (1, 6, 7, 18, 23, 34). Based on peptide composition and Chl/P7002 ratios, it is possible to classify the different PSI preparations into several levels of structural complexity. PSI particles produced by nonelectrophoretic methods are usually isolated in one of two forms, best represented by the PSI
Current Research in Photosynthesis, 1990
The complexity of the thylakoid membrane frequently necessitates its separation into component pa... more The complexity of the thylakoid membrane frequently necessitates its separation into component parts before meaningful analysis may be carried out. Thylakoid fractionation, typically via disruption of the bilayer with detergents, and subsequent manipulations required for various analytical techniques, always raises the question of the extent to which the solubilized experimental material is representative of the in vivo state. We report here on the application of a new native green gel system to five higher plant species. This system resolves as many as eighteen chlorophyll-protein complexes with very little release of free pigment and with a degree of preservation of subunit-subunit interactions that has not been obtainable with previous systems, suggesting that this system yields a more accurate picture of the native condition of the membrane. The system was originallydeveloped for use with Chlamydomonas thylakoids, from which up to twenty chlorophyll-protein complexes may be resolved (Allen and Staehelin, these Proceedings).
Developmental Biology, 1974
Developing muscle masses from hind limbs of lS-day fetal rats were freeze-cleaved, platinum and c... more Developing muscle masses from hind limbs of lS-day fetal rats were freeze-cleaved, platinum and carbon replicated, and examined electron microscopically. Gap junctions were observed linking cell pairs clearly identified as myogenic by the presence of easily recognized and characteristic arrays of cross or longitudinally fractured myofibrils. Occasionally gap junctions were also observed between identified nonmyogenic cells, but none were observed between myogenic-nonmyogenic cell pairs. Because the recently formed conjoint myogenic cells were already encapsulated by developing basal laminae and normally would have fused to form discrete myofibers, we suggest that this report provides additional evidence that gap junctions normally form immediately before and thus perhaps mediate the initial events of myogenic cell fusion in uiuo as well as in uitro.
Molecular biology of the cell, Jun 1, 2016
The preprophase band (PPB) is a cytokinetic apparatus that determines the site of cell division i... more The preprophase band (PPB) is a cytokinetic apparatus that determines the site of cell division in plants. It originates as a broad band of microtubules (MTs) in G2 and narrows to demarcate the future division site during late prophase. Studies with fluorescent probes have shown that PPBs contain F-actin during early stages of their development but become actin depleted in late prophase. Although this suggests that actins contribute to the early stages of PPB formation, how actins contribute to PPB-MT organization remains unsolved. To address this question, we used electron tomography to investigate the spatial relationship between microfilaments (MFs) and MTs at different stages of PPB assembly in onion cotyledon epidermal cells. We demonstrate that the PPB actins observed by fluorescence microscopy correspond to short, single MFs. A majority of the MFs are bound to MTs, with a subset forming MT-MF-MT bridging structures. During the later stages of PPB assembly, the MF-mediated lin...
Experimental Cell Research, 1974
Proceedings of the National Academy of Sciences, 1996
We have expressed a fusion protein formed between the avian infectious bronchitis virus M protein... more We have expressed a fusion protein formed between the avian infectious bronchitis virus M protein and the bacterial enzyme beta-glucuronidase in transgenic tobacco cells. Electron microscope images of such cells demonstrate that overexpression of this fusion protein gives rise to a type of endoplasmic reticulum membrane domain in which adjacent membranes become zippered together apparently as a consequence of the oligomerizing action of beta-glucuronidase. These zippered (Z-) membranes lack markers of the endoplasmic reticulum (NADH cytochrome c reductase and ribosomes) and accumulate in the cells in the form of multilayered scroll-like structures (up to 2 micrometers in diameter; 20-50 per cell) without affecting plant growth. The discovery of Z-membranes has broad implications for biology and biotechnology in that they provide a means for accumulating large quantities of recombinant membrane proteins within discrete domains of native membranes.
The Journal of Cell Biology, 1980
A highly purified chlorophyll a/b light-harvesting complex (chl a/b LHC; chl a/b ratio 1.2) was o... more A highly purified chlorophyll a/b light-harvesting complex (chl a/b LHC; chl a/b ratio 1.2) was obtained from Triton-solubilized chloroplast membranes of pea and barley according to the method of Burke et al. (1978, Arch. Biochem. Biophys. 187: 252--263). Gel electrophoresis of the cation-precipitated chl a/b LHC from peas reveals the presence of four polypeptides in the 23- to 28-kdalton size range. Three of these peptides appear to be identical to those derived from re-electrophoresed CPII and CPII* bands. In freeze-fracture replicas, the cation-precipitated chl a/b LHC appears as a semicrystalline aggregate of membranous sheets containing closely spaced granules. Upon removal of the cations by dialysis, the aggregates break up into their constituent membranous sheets without changing their granular substructure. These membranous sheets can be resolubilized in 1.5% Triton X-100, and the chl a/b LHC particles then reconstituted into soybean lecithin liposomes. Freeze-fracture micro...
PLANT PHYSIOLOGY, 1988
Characterization of the functional organization of the photochemical apparatus in the light sensi... more Characterization of the functional organization of the photochemical apparatus in the light sensitive chlorophyll b-deficient oil yellow-yellow green (OY-YG) mutant of maize (Zea mays) is presented. Spectrophotometric and kinetic analysis revealed substantially lower amounts of the light harvesting complex of photosystem II (LHCII-peripheral) in high light-grown OY-YG thylakoids. However, accumulation of a tightly bound LHCII appears unaffected by the lesion. Changes in photosystem (PS) stoichiometry include lower amounts of PSII with characteristic fast kinetics (PSIIa) and a substantial accumulation of PSII centers with characteristic slow kinetics (PSII,,) in the thylakoid membrane of the OY-YG mutant. Thus, PSII5, is the dominant photosystem in the mutant chloroplasts. In contrast to wild type, roughly 80% of the mutant PSII,, centers are functionally coupled to the plastoquinone pool and are probably localized in the appressed regions of the thylakoid membrane. These centers, designated PSII,J-QB-reducing (QB being the secondary electron quinone acceptor of PSII), are clearly distinct from the typical PSIIJ,-QB-nonreducing centers found in the stroma lamellae of wild-type chloroplasts. It is concluded that the observed changes in the stoichiometry of electrontransport complexes reflect the existence of a regulatory mechanism for the adjustment of photosystem stoichiometry in chloroplasts designed to correct any imbalance in light absorption by the two photosystems.
The Journal of Cell Biology, 1983
A chlorophyll-protein complex of chloroplast membranes, which simultaneously serves as light-harv... more A chlorophyll-protein complex of chloroplast membranes, which simultaneously serves as light-harvesting antenna and membrane adhesion factor, undergoes reversible, lateral diffusion between appressed and nonappressed membrane regions under the control of a protein kinase. The phosphorylation-dependent migration process regulates the amount of light energy that is delivered to the reaction centers of photosystems I and II (PS I and PS II), and thereby regulates their rate of turnover. This regulatory mechanism provides a rationale for the finding that the two photosystems are physically separated in chloroplast membranes (PS II in appressed, grana membranes, and PS I in nonappressed, stroma membranes). The feedback system involves the following steps: a membrane-bound kinase senses the rate of PS II vs. PS I turnover via the oxidation-reduction state of the plastoquinone pool, which shuttles electrons from PS II via cytochrome f to PS I. If activated, the kinase adds negative charge ...
Thelight-sensitive chlorophyll b(Chlb)-deficient oil yellow-yellow green (OY-YG)mutantofmaize(Zea... more Thelight-sensitive chlorophyll b(Chlb)-deficient oil yellow-yellow green (OY-YG)mutantofmaize(Zeamays)grownunderconditions ofhigh light exhibits differential reductions intheaccumulation ofthethree major Chlb-containing antenna complexes andcharacteristic changes inthy- lakoid architecture. Whenobserved byfreeze-fracture electron micro- scopy, themostnotable changes intheOY-YGthylakoid structure are: (a)a majorreduction inthenumberof8nanometer particles ofthe protoplasmic fracture face ofstacked membrane regions (PFs) paralleled bya60%reduction inthechlorophyll-proteins (CP)associated withthe peripheral light harvesting complex (LHCII) forphotosystem II(PSII) andwhichgive rise totheLHCIIoligomer/monomer (CPH*/CPII) bands onmildly dissociated greengels; (b)asizable decrease intheproportion of11to13nanometer particles oftheprotoplasmic fracture faceofun- stacked membraneregions (PFu) thatparallels theloss oflight harvesting complex I(LHCI) antennae fromphotosystem I(PSI) centers anda4...
The Plant cell, Jan 7, 2018
Biogenesis of the complex 3D architecture of plant thylakoids remains an unsolved problem. Here, ... more Biogenesis of the complex 3D architecture of plant thylakoids remains an unsolved problem. Here, we analyzed this process in chloroplasts of germinating Arabidopsis thaliana cotyledons using 3D electron microscopy and gene expression analyses of chloroplast proteins. Our study identified a linear developmental sequence with five assembly stages: tubulo-vesicular pro-thylakoids (24 HAI; hours after imbibition); sheet-like pre-granal thylakoids that develop from the pro-thylakoids (36 HAI); proliferation of pro-grana stacks with wide tubular connections to the originating pre-grana thylakoids (60 HAI); structural differentiation of pro-grana stacks and expanded stroma thylakoids (84 HAI); conversion of the pro-grana stacks into mature grana stacks (120 HAI). Development of the planar pre-granal thylakoids and the pro-grana membrane stacks coincides with the appearance of thylakoid-bound polysomes and photosystem II (PSII) complex subunits at 36 HAI. ATP synthase, cytochrome b6f and li...
Additional file 1: Figure S1. Gallery of tomographic reconstructions of Golgi stacks for each typ... more Additional file 1: Figure S1. Gallery of tomographic reconstructions of Golgi stacks for each type of tomographic sample studied (control, and 1, 4 and 6Â days BSA-induced). Each horizontal line represents a Golgi stack with cis cisternae colored orange and green, medial cisternae blue, pink and yellow, and trans cisternae colored purple and red. Within each group, the Golgi shown are from different cells. These data illustrate the inherent variability in structure of the Golgi cisternae. Bar 0.2Â Âľm.
Chris Somerville Carnegie Institution and Department of Biological Sciences, Stanford University ... more Chris Somerville Carnegie Institution and Department of Biological Sciences, Stanford University During the past 25 years, plant biologists have developed Arabidopsis into a very powerful tool for basic research. However, total federal funding for plant biology is less than 1% of the NIH budget. This ridiculous situation is not improved by having special interest groups within the plant biology community fighting for crumbs. I have long-believed that the heart of the problem is that plant biology is viewed as agriculture. Legislators view the big problem in agriculture as overproduction and do not see the point of further investments in basic research that might cause more overproduction. Additionally colleagues who work on crops species are likely to be first at the federal trough when the arguments are based on improving agriculture. I suggest that a more relevant social context for basic research in plant biology is energy. Although there is enough fossil fuel to meet our energy ...
Journal of Biological Research-Thessaloniki
Background: The insect-trapping leaves of Dionaea muscipula provide a model for studying the secr... more Background: The insect-trapping leaves of Dionaea muscipula provide a model for studying the secretory pathway of an inducible plant secretory system. The leaf glands were induced with bovine serum albumin to secrete proteases that were characterized via zymogram activity gels over a 6-day period. The accompanying morphological changes of the endoplasmic reticulum (ER) and Golgi were analyzed using 3D electron tomography of glands preserved by highpressure freezing/freeze substitution methods. Results: Secretion of multiple cysteine and aspartic proteases occurred biphasically. The majority of the Golgi was organized in clusters consisting of 3-6 stacks surrounded by a cage-like system of ER cisternae. In these clusters, all Golgi stacks were oriented with their cis-most C1 cisterna facing an ER export site. The C1 Golgi cisternae varied in size and shape consistent with the hypothesis that they form de novo. Following induction, the number of ER-bound polysomes doubled, but no increase in COPII vesicles was observed. Golgi changes included a reduction in the number of cisternae per stack and a doubling of cisternal volume without increased surface area. Polysaccharide molecules that form the sticky slime cause swelling of the trans and trans Golgi network (TGN) cisternae. Peeling of the trans-most cisternae gives rise to free TGN cisternae. One day after gland stimulation, the free TGNs were frequently associated with loose groups of oriented actin-like filaments which were not seen in any other samples. Conclusions: These findings suggest that the secretory apparatus of resting gland cells is "overbuilt" to enable the cells to rapidly up-regulate lytic enzyme production and secretion in response to prey trapping.
The use of registered names, trademarks, etc. in this publication does not imply, even in the abs... more The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.