Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy

Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon’s energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet–singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3–4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67–75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits—a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3–4 ps component is ascribed to equilibration with a “red” core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P₇₀₀ reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.

     

High frequency conversion of non-embryogenic synseeds and assessment of genetic stability through ISSR markers in <Emphasis Type="Italic">Gymnema sylvestre</Emphasis>

The present study describes the first attempt of exploiting encapsulation technology for high plantlet recovery, short-term storage and conservation of Gymnema sylvestre—an antidiabetic liana. Indole-3-butyric acid (IBA) pretreated nodal segments (NS) were encapsulated in sodium alginate (Na₂-alginate) matrix and the optimal culture conditions were evaluated in terms of maximum conversion capacity of synseeds into complete plantlets. Highest conversion frequency of synseeds was obtained on Murashige and Skoog’s (MS) medium supplemented with 5.0 µM 6-benzyladenine (BA). Augmentation of Na₂-alginate matrix with plant growth regulators (PGRs) and additive further improved in vitro conversion rates and the synthetic endosperm composed of 3% Na₂-alginate in MS?+?2.5 µM BA?+?2.5 µM gibberellic acid (GA₃)?+?50 µM adenine sulphate (AdS) stimulated maximum recovery (88.2?±?0.48%) of complete plantlets from synseeds. Studies on short term cold storage of synseeds showed that nutrient encapsulation maintains the viability of NS for a storage period of 8 weeks. Ex-vitro conversion of synseeds was also carried out on soilrite and vermicompost (3:1) mixture under culture room conditions. Monomorphic DNA profiles produced through Inter-Simple Sequence Repeat (ISSR) markers confirmed the genetic uniformity between synseed derived and mother plantlets.     

Dietary Supplementation of Selenium-Enriched Probiotics Enhances Meat Quality of Broiler Chickens (<Emphasis Type="Italic">Gallus gallus domesticus</Emphasis>) Raised Under High Ambient Temperature

We investigated the effects of selenium-enriched probiotics (SP) on broiler meat quality under high ambient temperature and explore their underlying mechanisms. A total of 200 1-day-old male broiler chicks (Ross 308) were randomly allotted to four treatment groups, each with five replicates, in groups of ten birds. These birds were fed a corn-soybean basal diet (C), a basal diet plus probiotics supplementation (P), a basal diet plus Se supplementation in the form of sodium selenite (SS, 0.30 mg Se/kg), and a basal diet with the addition of selenium-enriched probiotics (SP, 0.30 mg Se/kg). The experiment lasted for 42 days. The birds were sacrificed by cervical dislocation, and the breast muscles were removed for further process. Our results showed that SP diet significantly increased (p < 0.05) the physical (pH, colors, water holding capacity, drip loss, shear force) and sensory characteristics of breast meat. All P, SS, and SP supplementation enhanced the antioxidant system by increasing (p < 0.05) the Se concentrations, glutathione (GSH) levels, activities of glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) whereas decreasing (p < 0.05) malondialdehyde (MDA) levels, with SP being higher than P and SS. Moreover, SP diet significantly upregulated (p < 0.05) the mRNA levels of glutathione peroxidase genes (GPx1, GPx4) while it downregulated heat stress biomarkers such as heat shock protein (HSP) 70 as compared to C, P, and SS diets. In conclusion, our findings suggest that SP may function as beneficial nutritive supplement that is capable of improving meat quality during the summer season.     

Association of multiple-antibiotic-resistance profiles with point and nonpoint sources of Escherichia coli in Apalachicola Bay.

A total of 765 Escherichia coli isolates from point and nonpoint sources were collected from the Apalachicola National Estuarine Research Reserve, and their multiple-antibiotic-resistance (MAR) profiles were determined with 10 antibiotics. E. coli isolates from point sources showed significantly greater resistance (P < 0.05) to antibiotics and higher MAR indices than isolates from nonpoint sources. Specifically, 65 different resistance patterns were observed among point source isolates, compared to 32 among nonpoint source isolates. Examples of this contrast in MAR profiles included percentages of isolates with resistance to chlortetracycline-sulfathiazole of 33.7% and to chlortetracycline-penicillin G-sulfathiazole of 14.5% for point source isolates versus 15.4 and 1.7%, respectively, for nonpoint source isolates. MAR profile homology, based on coefficient similarity, showed that isolates from point sources were markedly more diverse than isolates from nonpoint sources. Seven clusters were observed among point source isolates, with a coefficient value of approximately 1.8. In contrast, only four clusters were observed among nonpoint source isolates. Covariance matrices of data displayed six very distinct foci representing nonpoint source E. coli isolates. Importantly, E. coli isolates obtained directly from human and animal feces also clustered among point and nonpoint sources, respectively. We conclude that E. coli MAR profiles were associated with point and nonpoint sources of pollution within Apalachicola Bay and that this method may be useful in facilitating management of other estuaries.     

Total synthesis,structural, and biological evaluation of stylissatin A and related analogs

The natural product cyclic peptide stylissatin A ( 1a ) was reported to inhibit nitric oxide production in LPS‐stimulated murine macrophage RAW 264.7 cells. In the current study, solid‐phase total synthesis of stylissatin A was performed by using a safety‐catch linker and yielded the peptide with a trans‐Phe⁷‐Pro⁶ linkage, whereas the natural product is the cis rotamer at this position as evidenced by a marked difference in NMR chemical shifts. In order to preclude the possibility of 1b being an epimer of the natural product, we repeated the synthesis using d ‐allo‐Ile in place of l ‐Ile and a different site for macrocyclization. The resulting product (d ‐allo‐Ile²)‐stylissatin A ( 1c ) was also found to have the trans‐Phe⁷‐Pro⁶ peptide conformations like rotamer 1b . Applying the second route to the synthesis of stylissatin A itself, we obtained stylissatin A natural rotamer 1a accompanied by rotamer 1b as the major product. Rotamers 1a , 1b , and the epimer 1c were separable by HPLC, and 1a was found to match the natural product in structure and biological activity. Six related analogs 2–7 of stylissatin A were synthesized on Wang resin and characterized by spectral analysis. The natural product ( 1a ), the rotamer ( 1b ), and (d ‐allo‐Ile²)‐stylissatin A ( 1c ) exhibited significant inhibition of NO^.. Further investigations were focused on 1b , which also inhibited proliferation of T‐cells and inflammatory cytokine IL‐2 production. The analogs 2–7 weakly inhibited NO^. production, but strongly inhibited IL‐2 cytokine production compared with synthetic peptide 1b . All analogs inhibited the proliferation of T‐cells, with analog 7 having the strongest effect. In the analogs, the Pro⁶ residue was replaced by Glu/Ala, and the SAR indicates that the nature of this residue plays a role in the biological function of these peptides. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

On the distributive pattern of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in the medulla oblongata of the golden hamster (Mesocricetus auratus). A study on the topographical and functional linkages of the two enzymes

Histochemical study on the distributive patterns of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), amongst the constituents of the medulla oblongata of golden hamster (Mesocricetus auratus), viewed through the angle of the possible topographical and functional linkage of the two enzymes, have provided identical set-ups of AChE and BChE in many of the nuclei, fibers and tracts. In the case of AChE in many instances the results further point out that there is a balance of the enzymatic activity between the nuclei and the associated processes. On the other hand, in relation to BChE activity, the nuclei and their processes do not seem to be linked through such a histochemical factor. A detailed discussion on the significance of AChE relationship between the neurons and their processes from the functional point of view, against the data available in the literature, has been incorporated in the present study. Histoenzymologically, the ranges of the activities of AChE and BChE amongst the neurons and their processes are so closely related that such components are mirror images of each other in histochemical patterns. Naturally, such results have led to a detailed discussion in the contribution culminating in a proposition that AChE and BChE (amongst the locales studied) seems to be intimately linked in the neuro-physiological functioning undergoing in the regions of the medulla oblongata of golden hamster.     

A comparative study of the ultrastructure of resting and active cambium of Salix fragilis,L.

Summary Cells of the resting cambium contain vesiculate smooth endoplasmic reticulum, free ribosomes, oil droplets, and protein bodies. There are comparatively few vacuoles, and these are small. The nucleus is fairly central within the cell and is surrounded by a cluster of plastids and mitochondria. Active cambial cells and young differentiating xylem elements are highly vacuolate, contain rough endoplasmic reticulum and polyribosomes, the Golgi apparatus is active in the production of vesicles, and the distribution of organelles is a function of the vacuolation of the cell.It is suggested that the lipid droplets and protein bodies are storage materials which are required during the first stages of differentiation at the beginning of the growing period.     

Two new species of Cephalobellus Cobb, 1920 (Thelastomatidae: Nematoda) from coleopteran larvae from India

Summary Two new species of Cephalobellus, C. annulobellus and C. spicatus, collected from unidentified coleopteran larvae in Aligarh, India, are described and figured. Both species have characteristic closely set annules in the cervical region of their females and five pairs of caudal papillae and lateral alae in the males. C. annulobellus possesses a labial disc, has a smaller body and different shape and arrangement of caudal papillae than in C. spicatus. A key to the species of Cephalobellus is given. ac]19830610     

Light-adapted charge-separated state of photosystem II: structural and functional dynamics of the closed reaction center

Photosystem II (PSII) uses solar energy to oxidize water and delivers electrons for life on Earth. The photochemical reaction center of PSII is known to possess two stationary states. In the open state (PSII_O), the absorption of a single photon triggers electron-transfer steps, which convert PSII into the charge-separated closed state (PSII_C). Here, by using steady-state and time-resolved spectroscopic techniques on Spinacia oleracea and Thermosynechococcus vulcanus preparations, we show that additional illumination gradually transforms PSII_C into a light-adapted charge-separated state (PSII_L). The PSII_C-to-PSII_L transition, observed at all temperatures between 80 and 308 K, is responsible for a large part of the variable chlorophyll-a fluorescence (F_v) and is associated with subtle, dark-reversible reorganizations in the core complexes, protein conformational changes at noncryogenic temperatures, and marked variations in the rates of photochemical and photophysical reactions. The build-up of PSII_L requires a series of light-induced events generating rapidly recombining primary radical pairs, spaced by sufficient waiting times between these events—pointing to the roles of local electric-field transients and dielectric relaxation processes. We show that the maximum fluorescence level, F_m, is associated with PSII_L rather than with PSII_C, and thus the F_v/F_m parameter cannot be equated with the quantum efficiency of PSII photochemistry. Our findings resolve the controversies and explain the peculiar features of chlorophyll-a fluorescence kinetics, a tool to monitor the functional activity and the structural-functional plasticity of PSII in different wild-types and mutant organisms and under stress conditions.

The closed-state of photosystem II possesses a hitherto unrecognized structural and functional plasticity and upon illumination assumes a light-adapted charge-separated state.