Stromal Side Research Articles

Intra- and inter-monomeric transfers in the light harvesting LHCII complex: the Redfield–Förster picture

We further develop the model of energy transfer in the LHCII trimer based on a quantitative fit of the linear spectra (including absorption (OD), linear dichroism (LD), circular dichroism (CD), and fluorescence (FL)) and transient absorption (TA) kinetics upon 650 nm and 662 nm excitation. The spectral shapes and relaxation/migration rates have been calculated using the combined Redfield-Förster approach capable of correctly describing fast relaxation within strongly coupled chlorophyll (Chl) a and b clusters and slow migration between them. Within each monomeric subunit of the trimeric complex there is fast (sub-ps) conversion from Chl's b to Chl's a at the stromal side accompanied by slow (>10 ps) equilibration between the stromal- and lumenal-side Chl a clusters in combination with slow (>13 ps) population of Chl's a from the 'bottleneck' Chl a604 site. The connection between monomeric subunits is determined by exciton coupling between the stromal-side Chl's b from the two adjacent subunits (Chl b601'-608-609 cluster) making a simultaneous fast (sub-ps) population of the Chl's a possible from both subunits. Final equilibration occurs via slow (>20 ps) migration between the Chl a clusters located on different monomeric subunits. This migration includes up-hill transfers from the red-most Chl a610-611-612 clusters located at the peripheral side in each subunit to the Chl a602-603 dimers located at the inner side of the trimeric LHCII complex.

Energy transfer processes in the isolated core antenna complexes CP43 and CP47 of photosystem II

The energy equilibration and transfer processes in the isolated core antenna complexes CP43 and CP47 of photosystem II have been studied by steady-state and ultrafast (femto- to nanosecond) time-resolved spectroscopy at room temperature. The annihilation-free femtosecond absorption data can be described by surprisingly simple sequential kinetic models, in which the excitation energy transfer between blue and red states in both antenna complexes is dominated by sub-picosecond processes and is completed in less than 2 ps. The slowest energy transfer steps with lifetimes in the range of 1–2 ps are assigned to transfer steps between the chlorophyll layers located on the stromal and lumenal sides. We conclude that these ultrafast intra-antenna energy transfer steps do not represent a bottleneck in the rate of the primary processes in intact photosystem II. Since the experimental energy equilibration rates are up to a factor of 3–5 higher than concluded previously, our results challenge the conclusions drawn from theoretical modeling.

Opioids affect focal contact-mediated cell–substrate adhesion

Earlier observations suggested that opioids modify cell-substrate adhesion on agar. In this study, we wanted to investigate whether opioids also interfere with cell adhesion to biologically relevant substrates, including interstitial matrix and basement membrane components. Human embryonic kidney 293 cells stably transfected with FLAG-tagged micro-opioid receptor were used as an experimental model. The cells were cultured on tissue culture plastic, collagen types I and IV, fibronectin, laminin and human amnion fragments in the absence or presence of morphine. Cultures were immunolabelled with antivinculin to visualize focal contacts. Morphine-treated cultures on tissue culture plastic, collagen types I and IV and fibronectin, but not on laminin, covered less substrate than untreated cultures; individual cells were difficult to distinguish and their nuclei piled up in contrast to untreated cultures. The same effects were observed on human amnion fragments: morphine changed the morphotype of cultures on the stromal side, but not on the basement membrane side. Cultures that were treated with morphine displayed fewer focal contacts than untreated cultures on collagen type I, whereas untreated and morphine-treated cultures were indistinguishable on laminin.

The Effect of Femtosecond Laser Lamellar Dissection at Various Depths on Corneal Endothelium in the Recipient Bed of the Porcine Eye

To evaluate the effect of femtosecond laser lamellar dissection on corneal endothelium ultrastructure and viability. Newly enucleated porcine eyes (N = 32) were used. The eyes were divided into four groups and a 7.5-mm diameter corneal lamellar dissection with the same size side cut at various depths was performed using a 60-kHz femtosecond laser with raster and spiral lamellar pattern. The endothelium was examined using scanning electron microscopy and light microscopy with Alizarin red staining. All four groups showed similar corneal endothelial cell morphology and viability at the center of the endothelium regardless of the lamellar cut pattern (P > .05). In groups 2 and 3, linear dotted endothelial cell damage or folding correlating with the side cut was observed. Using femtosecond lasers for stromal dissection and side cutting was safe for the central endothelium and caused only minimal damage to the peripheral endothelium, regardless of the laser emission pattern.

The Stromal Chloroplast Deg7 Protease Participates in the Repair of Photosystem II after Photoinhibition in Arabidopsis

Light is the ultimate source of energy for photosynthesis; however, excessive light leads to photooxidative damage and hence reduced photosynthetic efficiency, especially when combined with other abiotic stresses. Although the photosystem II (PSII) reaction center D1 protein is the primary target of photooxidative damage, other PSII core proteins are also damaged and degraded. However, it is still largely unknown whether degradation of D1 and other PSII proteins involves previously uncharacterized proteases. Here, we show that Deg7 is peripherally associated with the stromal side of the thylakoid membranes and that Deg7 interacts directly with PSII. Our results show that Deg7 is involved in the primary cleavage of photodamaged D1, D2, CP47, and CP43 and that this activity is essential for its function in PSII repair. The double mutants deg5 deg7 and deg8 deg7 showed no obvious phenotypic differences under normal growth conditions, but additive effects were observed under high light. These results suggest that Deg proteases on both the stromal and luminal sides of the thylakoid membranes are important for the efficient PSII repair in Arabidopsis (Arabidopsis thaliana).

Effective Keratocyte Culture Using Amniotic Membrane Matrix and Differentiation of Mesenchymal Stem Cells

Purpose: To investigate the characteristics of cultured rabbit corneal keratocytes in vitro and evaluate the possibility of differentiation of mesenchymal stem cells to keratocytes using the keratocyte conditioned medium (KCM). Methods: Isolated keratocytes were seeded on the stromal side of amniotic membranes (AM) or plastic dishes, and morphologic changes were evaluated. Rabbit mesenchymal stem cells were cultured on AM with -MEM (minimum essential medium alpha) and KCM. The gene expression patterns of specific keratocyte markers (keratocan, lumican, and aldehyde dehydrogenase family, member A1 (ALDH1A1)) of cultured cells were evaluated by RT-PCR. Results: Keratocytes on AM showed dendritic morphology with slow proliferation in contrast, cells on dishes were stellate in shape with fast proliferation. Cultured keratocytes on AM maintained the expression of keratocan, lumican and ALDH1A1 while keratocytes on plastic dishes steadily lost their keratocyte marker gene expression. Additionally, mesenchymal stem cells cultured with KCM on AM induced expression of keratocan and ALDH1A1. Conclusions: Keratocytes cultured on AM stromal matrix maintained their characteristic morphology and marker gene expression. Morphology changes and marker gene expressions of mesenchymal stem cells suggest an ability to differentiate into keratocytes when grown on AM with KCM.

Supramolecular organization of phycobiliproteins in the chlorophyll d-containing cyanobacterium Acaryochloris marina

Here we report the high-resolution detail of the organization of phycobiliprotein structures associated with photosynthetic membranes of the chlorophyll d-containing cyanobacterium Acaryochloris marina. Cryo-electron transmission-microscopy on native cell sections show extensive patches of near-crystalline phycobiliprotein rods that are associated with the stromal side of photosynthetic membranes. This supramolecular photosynthetic structure represents a novel mechanism of organizing the photosynthetic light-harvesting machinery. In addition, the specific location of phycobiliprotein patches suggests a physical separation of photosystem I and photosystem II reaction centres. Based on this finding and the known photosystem’s structure in Acaryochloris, we discuss possible membrane arrangements of photosynthetic membrane complexes in this species.

Biogenesis of cytochrome b6 in photosynthetic membranes

In chloroplasts, binding of a c′-heme to cytochrome b6 on the stromal side of the thylakoid membranes requires a specific mechanism distinct from the one at work for c-heme binding to cytochromes f and c6 on the lumenal side of membranes. Here, we show that the major protein components of this pathway, the CCBs, are bona fide transmembrane proteins. We demonstrate their association in a series of hetero-oligomeric complexes, some of which interact transiently with cytochrome b6 in the process of heme delivery to the apoprotein. In addition, we provide preliminary evidence for functional assembly of cytochrome b6f complexes even in the absence of c′-heme binding to cytochrome b6. Finally, we present a sequential model for apo- to holo-cytochrome b6 maturation integrated within the assembly pathway of b6f complexes in the thylakoid membranes.

Stratification of antigen-presenting cells within the normal cornea (39.57)

Abstract The composition and location of professional antigen presenting cells (APC) varies in different mucosal surfaces. The cornea, long considered an immune privileged tissue devoid of APCs is now known to host a network of bone marrow-derived cells. Here, we utilized transgenic mice that express EGFP from the CD11c promoter in conjunction with immunohistochemical staining to demonstrate an interesting stratification of APCs within non-inflamed murine corneas. CD11c+ DCs reside in the basal epithelium, many seemingly embedded in the basement membrane. Most DCs express MHC class II on at least some dendrites, which extended up to 50 µm in length and traversed up 20 µm tangentially nearly to the apical surface of the epithelium. The DC density diminished from peripheral to central cornea. Beneath the DCs and adjacent to the stromal side of the basement membrane reside CD11c-CD11b+ presumed macrophages that expressed low levels of MHC class II. Finally, MHC class II- CD11b+ cells filled the remainder of the stroma. This highly reproducible stratification of bone marrow-derived cells is suggestive of progression from APC to barrier function.

Loss of peripheral polypeptides in the stromal side of photosystem I by light-chilling in cucumber leaves.

Photosystem I (PSI) is severely damaged by chilling at 4 degrees C in low light, especially in the chilling sensitive plant cucumber. To investigate the early events in PSI photoinhibition, we examined structural changes in the level of pigment-protein complexes in cucumber leaves in comparison with pea leaves. The complexes were separated on a native green gel and an increase in the intensity of a band was observed only in light-chilled cucumber leaves. The 77 K fluorescence emission spectrum of this green band indicated that the band was mainly composed of PSI with light-harvesting complex I. Each lane was cut from the green gel and separated on a fully denaturing SDS-PAGE in the second dimension. The new green gel band observed after light-chilling in cucumber leaves lacked 19, 18, and 16.5 kDa polypeptides. These results suggest that light-chilling facilitates the release of three peripheral polypeptides as an early event of chilling stress in vivo, which results in the inactivation of PSI in intact cucumber leaves.

Analysis of the Chloroplast Protein Kinase Stt7 during State Transitions

State transitions allow for the balancing of the light excitation energy between photosystem I and photosystem II and for optimal photosynthetic activity when photosynthetic organisms are subjected to changing light conditions. This process is regulated by the redox state of the plastoquinone pool through the Stt7/STN7 protein kinase required for phosphorylation of the light-harvesting complex LHCII and for the reversible displacement of the mobile LHCII between the photosystems. We show that Stt7 is associated with photosynthetic complexes including LHCII, photosystem I, and the cytochrome b 6 f complex. Our data reveal that Stt7 acts in catalytic amounts. We also provide evidence that Stt7 contains a transmembrane region that separates its catalytic kinase domain on the stromal side from its N-terminal end in the thylakoid lumen with two conserved Cys that are critical for its activity and state transitions. On the basis of these data, we propose that the activity of Stt7 is regulated through its transmembrane domain and that a disulfide bond between the two lumen Cys is essential for its activity. The high-light–induced reduction of this bond may occur through a transthylakoid thiol–reducing pathway driven by the ferredoxin-thioredoxin system which is also required for cytochrome b 6 f assembly and heme biogenesis.

Phycobiliprotein diffusion in chloroplasts of cryptophyte Rhodomonas CS24

Unicellular cryptophyte algae employ antenna proteins with phycobilin chromophores in their photosynthetic machinery. The mechanism of light harvesting in these organisms is significantly different than the energy funneling processes in phycobilisomes utilized by cyanobacteria and red algae. One of the most striking features of cryptophytes is the location of the water-soluble phycobiliproteins, which are contained within the intrathylakoid spaces and are not on the stromal side of the lamellae as in the red algae and cyanobacteria. Studies of mobility of phycobiliproteins at the lumenal side of the thylakoid membranes and how their diffusional behavior may influence the energy funneling steps in light harvesting are reported. Confocal microscopy and fluorescence recovery after photobleaching (FRAP) are used to measure the diffusion coefficient of phycoerythrin 545 (PE545), the primary light harvesting protein of Rhodomonas CS24, in vivo. It is concluded that the diffusion of PE545 in the lumen is inhibited, suggesting possible membrane association or aggregation as a potential source of mobility hindrance.

Flipping the Inverted Donor Disk in Descemet Stripping Automated Endothelial Keratoplasty

We describe a technique we used to flip the donor corneal lenticule during Descemet stripping automated endothelial keratoplasty. In this case, in which we performed standard phacoemulsification and intraocular lens implantation as a combined procedure with Descemet stripping automated endothelial keratoplasty, the donor lenticule unfolded upside down in the anterior chamber (AC). To flip the donor to a stromal side up position with minimum manipulation, we first passed in a needle and fixed it on the edge of the lenticule. This needle was used to push the edge of the lenticule upward while we filled up the AC with balanced salt solution, directing the fluid to push the distal edge down and away. Having flipped the lenticule halfway, the procedure was continued by placing the needle on the midperipheral stroma of the donor lenticule and sliding it toward the recipient cornea. Then, the AC was filled with air to allow adhesion of the donor, and at the end of surgery, the air was replaced with balanced salt solution. The cornea cleared over a period of 10 days after surgery. At the end of the fourth postoperative week, the final best-corrected visual acuity was 20/50.

Changes in the localization of collagens IV and VIII in corneas obtained from patients with posterior polymorphous corneal dystrophy

Posterior polymorphous corneal dystrophy (PPCD) is a hereditary bilateral disorder affecting primarily the endothelium and Descemet's membrane (DM). The aim of this study was to determine the changes in the presence and localization of the alpha1-alpha6 collagen IV chains and alpha1, alpha2 collagen VIII chains in Czech patients with PPCD. Twelve corneal buttons from ten PPCD patients who underwent corneal grafting, as well as eight unaffected corneas, were used. Enzymatic indirect immunohistochemistry was performed on cryosections using antibodies against the alpha1-alpha6 collagen IV chains and alpha1, alpha2 collagen VIII chains. The intensity of the signal was examined separately in the basal membrane of the epithelium (BME), stroma and DM. More than 50% of PPCD specimens exhibited positivity for alpha1 and alpha2 collagen IV chains in the BME and in the posterior stroma, while no staining was detected in these areas in control specimens. The signal for the alpha1 and alpha2 collagen IV chains was more intense in DM of PPCD corneas compared to controls and it was shifted from the stromal side (in control tissue) to the endothelial side of DM (in the patients). A less intensive signal in PPCD corneas for the alpha3 and alpha5 chains in DM and an accumulation of alpha3-alpha5 in the posterior stroma in diseased corneas were the only differences in staining for the alpha3-alpha6 collagen IV chains. The alpha1 collagen VIII chain was detected on both the endothelial and the stromal sides of DM in 90% of patients with PPCD, compared with the prevailing localization on the stromal side of DM in control corneas. A change in the localization of the alpha2 collagen VIII chain in DM from vertically striated features in control specimens to double line positivity in the DM of PPCD corneas and positive staining in the posterior collagenous layer of four patients were also detected. In three PPCD patients a fibrous pannus located under the BME, positive for alpha1-alpha3, alpha5 collagen IV chains and alpha1 collagen VIII chain, was observed. The increased expression of the alpha1, alpha2 collagen IV and alpha1 collagen VIII chains and the change in their localization in DM may contribute to the increased endothelial proliferative capacity observed in PPCD patients.

S.95. Apoptotic and Necrotic Effect of the Stromal and Epithelial Side of the Amniotic Membrane on Human Peripheral Blood Mononuclear Cells

S.95. Apoptotic and Necrotic Effect of the Stromal and Epithelial Side of the Amniotic Membrane on Human Peripheral Blood Mononuclear Cells

Use of tissue adhesives in ophthalmology

Use of tissue adhesives in ophthalmology

Stratification of Antigen-presenting Cells within the Normal Cornea

The composition and location of professional antigen presenting cells (APC) varies in different mucosal surfaces. The cornea, long considered an immune-privileged tissue devoid of APCs, is now known to host a heterogeneous network of bone marrow-derived cells. Here, we utilized transgenic mice that express enhanced green fluorescent protein (EGFP) from the CD11c promoter (pCD11c) in conjunction with immunohistochemical staining to demonstrate an interesting stratification of APCs within non-inflamed murine corneas. pCD11c(+) dendritic cells (DCs) reside in the basal epithelium, seemingly embedded in the basement membrane. Most DCs express MHC class II on at least some dendrites, which extend up to 50 µm in length and traverse up 20 µm tangentially towards the apical surface of the epithelium. The DC density diminishes from peripheral to central cornea. Beneath the DCs and adjacent to the stromal side of the basement membrane reside pCD11c(-) CD11b(+) putative macrophages that express low levels of MHC class II. Finally, MHC class II(-)pCD11c(-) CD11b(+) cells form a network throughout the remainder of the stroma. This highly reproducible stratification of bone marrow-derived cells is suggestive of a progression from an APC function at the exposed corneal surface to an innate immune barrier function deeper in the stroma.

Two short‐chain dehydrogenase/reductases, NON‐YELLOW COLORING 1 and NYC1‐LIKE, are required for chlorophyll b and light‐harvesting complex II degradation during senescence in rice

Yellowing, which is related to the degradation of chlorophyll and chlorophyll-protein complexes, is a notable phenomenon during leaf senescence. NON-YELLOW COLORING 1 (NYC1) in rice encodes a membrane-localized short-chain dehydrogenase/reductase (SDR) that is thought to represent a chlorophyll b reductase necessary for catalyzing the first step of chlorophyll b degradation. Analysis of the nyc1 mutant, which shows the stay-green phenotype, revealed that chlorophyll b degradation is required for the degradation of light-harvesting complex II and thylakoid grana in leaf senescence. Phylogenetic analysis further revealed the existence of NYC1-LIKE (NOL) as the most closely related protein to NYC1. In the present paper, the nol mutant in rice was also found to show a stay-green phenotype very similar to that of the nyc1 mutant, i.e. the degradation of chlorophyll b was severely inhibited and light-harvesting complex II was selectively retained during senescence, resulting in the retention of thylakoid grana even at a late stage of senescence. The nyc1 nol double mutant did not show prominent enhancement of inhibition of chlorophyll degradation. NOL was localized on the stromal side of the thylakoid membrane despite the lack of a transmembrane domain. Immunoprecipitation analysis revealed that NOL and NYC1 interact physically in vitro. These observations suggest that NOL and NYC1 are co-localized in the thylakoid membrane and act in the form of a complex as a chlorophyll b reductase in rice.

Redox Reactions of the Non-Heme Iron in Photosystem II: An EPR Spectroscopic Study

Photosystem II (PSII) contains a non-heme ferrous ion, located on the stromal side of the protein in close proximity to quinones A and B (Q(A) and Q(B)). We used EPR spectroscopy to examine the temperature-dependent redox reactions of the iron-quinone site, using it as a probe of potentially physiologically relevant proton-coupled electron-transfer (PCET) reactions. Complete chemical oxidation of the non-heme iron at ambient temperatures was followed by cryogenic photoreduction, producing a temperature-dependent yield of Fe(2+)Q(A) (or Fe(3+)Q(A)(-))...Chl(+)/Car(+)/Y(D)(*) charge separations. These charge separations were subsequently observed to partially recombine in the dark at cryogenic temperatures. We observed no double photochemical charge separations upon illumination at temperatures <or=30 K, demonstrating that Q(A) and Fe(3+) together act as a single electron-accepting moiety at very low temperatures. Our results indicate the existence of two populations of the iron-quinone site in PSII, one whose Fe(3+) signal is abolished by illumination at liquid helium temperatures and one whose Fe(3+) signal is abolished by illumination only above 75 K. The observation of non-heme iron photoreduction at cryogenic temperatures (possibly at liquid helium temperatures and certainly above 75 K) implies the existence of a low reorganization energy proton-transfer (ET) pathway within the protein to the non-heme iron environment, of possible relevance to the PCET reactions of Q(B) and/or the non-heme iron itself. Furthermore, we observed the partial reoxidation of the non-heme iron by charge recombination with previously oxidized chlorophyll, carotenoid, and Y(D) within PSII. This electron transfer might be important in the photoprotective transfer of oxidative power away from P(680)(+) and the oxygen-evolving complex in stressed PSII centers.

Plastid division: across time and space

Plastid division is executed by the coordinated action of at least two molecular machineries--an internal machinery situated on the stromal side of the inner envelope membrane that was contributed by the cyanobacterial endosymbiont from which plastids evolved, and an external machinery situated on the cytosolic side of the outer envelope membrane that was contributed by the host. Here we review progress in defining the components of the plastid division complex and understanding the mechanisms of envelope constriction and division-site placement in plants. We also highlight recent work identifying the first molecular linkage between the internal and external division machineries, shedding light on how their mid-plastid positioning is coordinated across the envelope membranes. Little is known about the mechanisms that regulate plastid division in plant cells, but recent studies have begun to hint at potential mechanisms.