1,721,223 research outputs found
Photoinhibition in vivo and in vitro involves weakly coupled chlorophyll-protein complexes
No full textIn the present study the analysis of the relation between the excited state population in the photosystem 11 (PSII) antenna and photoinactivation has been extended from an in vitro system, isolated thylakoids, to an in vivo system, Chlamydomonas reinhardtii cells. The results indicate that the excited state quenching by an added singlet quencher induces maximal protection against photoinhibition of about 30% of that expected on the basis of the observed light intensity-treatment time reciprocity rule. Similar results, obtained previously with thylakoids, have been interpreted in terms of damaged or incorrectly assembled complexes that play an important role in photoinhibition in the thylakoid membranes (Santabarbara, S., K. Neverov, F. M. Garlaschi, G. Zucchelli and R. C. Jennings [2001] Involvement of uncoupled antenna chlorophylls in photoinhibition in thylakoids. FEBS Lett. 491, 109-113.). In an attempt to better define this aspect, the photoinhibition action spectra were determined for mutant barley thylakoids, lacking the chlorophyll (Chl) a-b complexes of the outer antenna, and for its wild type. The results indicate that in both systems the action spectra are significantly blueshifted (2-4 nm) and are broader than the PSII absorption in the membranes. These data are interpreted in terms of a heterogeneous population of outer and inner antenna pigment-protein complexes that contain significant levels of uncoupled Chl
Ergodicity, configurational entropy and free energy in pigment solutions and plant photosystems : influence of excited state lifetime
No full textWe examine ergodicity and configurational entropy for a dilute pigment solution and for a suspension of plant photosystem particles in which both ground and excited state pigments are present. It is concluded that the pigment solution, due to the extreme brevity of the excited state lifetime, is non-ergodic and the configurational entropy approaches zero. Conversely, due to the rapid energy transfer among pigments, each photosystem is ergodic and the configurational entropy is positive. This decreases the free energy of the single photosystem pigment array by a small amount. On the other hand, the suspension of photosystems is non-ergodic and the configurational entropy approaches zero. The overall configurational entropy which, in principle, includes contributions from both the single excited photosystems and the suspension which contains excited photosystems, also approaches zero. Thus the configurational entropy upon photon absorption by either a pigment solution or a suspension of photosystem particles is approximately zero
Antenna entropy in plant photosystems does not reduce the free energy for primary charge separation
Full text linkWe have investigated the concept of the so-called "antenna entropy" of higher plant photosystems. Several interesting points emerge:
1. In the case of a photosystem which harbours an excited state, the "antenna entropy" is equivalent to the configurational (mixing) entropy of a thermodynamic canonical ensemble. The energy associated with this parameter has been calculated for a hypothetical isoenergetic photosystem, photosystem I and photosystem II, and comes out in the range of 3.5 - 8% of the photon energy considering 680 nm.
2. The "antenna entropy" seems to be a rather unique thermodynamic phenomenon, in as much as it does not modify the free energy available for primary photochemistry, as has been previously suggested.
3. It is underlined that this configurational (mixing) entropy, unlike heat dispersal in a thermal system, does not involve energy dilution. This points out an important difference between thermal and electronic energy dispersal
A novel biopsy technique for lesions involvinginterproximal soft tissues
No full textBackground: Biopsy of soft tissues around teeth can cause periodontal deficiency with several side effects. When the neoformation involves frontal areas biopsy often induces an aesthetic impairment, particularly critical when the interdental papilla is entailed. Description of the procedure: A new surgical approach to treat lesions involving interdental tissues is described. The flap design is characterized by a sub-marginal scalloped incision, possibly confined into the keratinized tissue at the vestibular side. The incision starts 1 mm above the lesion, in the midline between the two confining teeth. With a parabolic shape, the incision reaches the gingival margin at the distal line angle of the distal tooth. Hence, another parabolic incision is performed connecting the starting point with the marginal mesial line angle of the mesial tooth. After this step, two options are applied depending on the lesion extension. When the lesion is confined coronally to the line connecting the gingival margin zeniths of the two adjacent teeth, oblique linear incisions are performed till to the gingival margin zeniths. Otherwise, when the lesion extends beyond this line, two parabolic incisions are per-formed on both adjacent teeth, till to the distal and mesial line angle respectively. Specific anatomic measurements rule up the incisional design. For the palatal/lingual side, the incision follows the principles of a general excisional procedure. Intrasulcular incisions are then made and the lesion with surrounding tissues are collected for examination. Both full-thickness and split-thickness are used for the buccal flap elevation. De-epithelized the adjacent anatomic papillae, two sling sutures are used to stabilize the entire flap to the most feasible coronal position. Generally single sutures are used for the palatal side and the eventual graft. Outcomes: All 9 cases treated so far have ever shown an esthetically satisfying outcome without recurrence or adverse events. Conclusions: This technique allows clinician to restore gingival health preserving aesthetics and function
Coronally advanced flap: a modified surgical approach for isolated recession-type defects: three-year results.
No full textVarious modifications of the coronally displaced flap have been proposed in the literature with the attempt of treating gingival recession with uneven predictable results. The goal of the present study was to evaluate the effectiveness with respect to root coverage of a modification of the coronally advanced flap procedure for the treatment of isolated recession-type defects in the upper jaw. Methods: Forty isolated gingival recessions with at least 1 mm of keratinized tissue apical to the defects were treated with a modified approach to the coronally advanced flap. The main change in the surgical procedure consisted in the modification of flap thickness and dimension of surgical papillae during flap elevation. All recessions fall into Miller class I or II. The clinical re-evaluation was performed 1 year and 3 years after the surgery. Results: At the 1-year examination, the average root coverage was 3.72 ± 1.0 mm (98.6% of the pre-operative recession depth) and 3.64 ± 1.1 mm (96.7%) at 3 years. The gain in probing attachment amounted to 3.65 ± 1.10 mm at 1 year and to 3.70 ± 1.09 mm at 3 years. The average increase of keratinized tissue between the baseline and the 3-year follow-up amounted to 1.78 ± 0.90 mm. All changes of keratinized tissue (difference between baseline and 1 year, baseline and 3 years, and between 1 and 3 years) were statistically significant. Conclusion: The modified coronally advanced surgical technique is effective in the treatment of isolated gingival recession in the upper ja
The Q(y) absorption transition of the light harvesting complex II as determined by structure based analysis of chlorophyll nmacrocycle deforemations
No full textThe absorption spectrum of the main antenna complex of photosystem II, LHCII, has been modeled using, as starting points, the chlorophyll (chl) atomic coordinates as obtained by the LHCII crystal analysis [Liu, Z., Yan, H., Wang, K., Kuang, T., Zhang, J., Gui, L., An, X., and Chang, W. (2004) Nature 428, 287-292] of three different trimers. The chl site Q(y) transition energies have been obtained in terms of the chl macrocycle deformations influencing the energy level of the chl frontier orbitals. Using these chl site transition energy values and the entire set of interaction energies, calculated in the ideal dipole approximation, the complete Hamiltonians for the three LHCII trimers have been written and the full set of 42 eigenstates of each LHCII trimer have been calculated. With the 42 transition energies and transition dipole strengths, either unperturbed or associated to the eigenstates, the LHCII Q(y) absorption spectrum has been calculated using a chl absorption band shape. These calculations have been performed both in vacuo and in the presence of a medium. Despite the number of approximations, a good correlation with the measured absorption spectrum of a LHCII preparation is obtained. This analysis shows that, although a substantial C3 symmetry of the LHCII trimer in terms of both chl-chl distances and interaction energies is present, a marked variation among monomer subsets of site transition energies is estimated. This leads to a C3 symmetry breaking in the unperturbed chl site transition energies set and, consequently, in the trimer eigenstates. It is also concluded that interactions among chlorophylls do not significantly modify the light absorption role of LHCII in plant leaves
GTR treatment of intrabony defects in patients with early-onset and chronic adult periodontitis
No full textLa GTR nel trattamento dei difetti infraossei in pazienti con parodontiti ad esordio precoce
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