The triplet state of the primary donor of the photosynthetic bacterium Rhodopseudomonas viridis

The absorbance-detected magnetic-resonance technique has been applied to the study of the triplet state of the primary donor in chromatophores of the photosynthetic bacterium Rps. viridis. The results confirm the triplet-minus-singlet absorbance-difference spectrum and its interpretation as previously obtained for isolated reaction centers (Den Blanken, H.J. and Hoff, A.J. (1982) Biochim. Biophys. Acta 681, 365–374). Our present results affirm that the primary donor is a bacteriochlorophyll b dimer, and that there is no blue exciton band at 850 nm. We show that the reaction centers are not identical, but have a small heterogeneity in their properties. In chromatophores and sometimes in isolated reaction centers a shoulder is observed in the long-wavelength absorbance-difference band of the primary donor. This shoulder is possibly caused by charge transfer interaction of the donor with an adjacent chromophore (Vermeglio, A. and Paillotin. G. (1982) Biochim. Biophys. Acta 681, 32–40; Maslov, V.G., Klevanik, A.V., Ismailov, M.A. and Shuvalov, V.A. (1983) Doklady Akad. Nauk. SSSR 269, 1217–1221) or it reflects a slight heterogeneity in the reaction-center geometry, which cannot be removed with the selection offered by the magnetic resonance technique. The zero-field triplet-ESR spectrum and the sublevel decay rates of the triplet state of the primary donor are presented, as detected in whole cells at the antenna fluorescence, and in chromatophores and isolated reaction centers at the absorbance-difference band at 838 nm. We do not observe the expected reversal of the sign of the ESR transitions monitored with the two techniques. A tentative explanation is given in terms of energy transfer from unrelaxed excited states of the antenna pigments to the reaction center.     

PHYLOGENETIC POSITION OF BOLBOCOLEON PILIFERUM (ULVOPHYCEAE,CHLOROPHYTA): EVIDENCE FROM REPRODUCTION,ZOOSPORE AND GAMETE ULTRASTRUCTURE,AND SMALL SUBUNIT RRNA GENE SEQUENCES1

Aspects of the reproduction of Bolbocoleon piliferum N. Pringsheim, a common, small, filamentous, endophytic marine green alga, were examined by LM and TEM. These observations were combined with phylogenetic analysis of nuclear‐encoded small subunit rRNA gene sequences to assess the phylogenetic position of B. piliferum. Quadriflagellate zoospores and planozygotes derived from fusion of isogametes yielded plants with identical morphology. Zoosporangia and gametangia divided by sequential cleavages. Plugs at the apices of zoosporangia and gametangia formed during development; tubes were found at zoosporangial and gametangial apices after swarmer release. Flagellar apparatuses of zoospores and gametes were similar to those of algae in the Ulvales (Ulvophyceae), except that terminal caps were entire rather than bilobed and rhizoplasts and “stacked” microtubular root configurations were absent. Structures associated with planozygotes were identical to those observed in other algae currently assigned to Ulotrichales and Ulvales. Molecular phylogenetic analyses placed B. piliferum within the Ulvophyceae, at the base of a clade that contains representatives of the families Ulvaceae, Ulvellaceae, and Kornmanniaceae. The results support an earlier hypothesis that B. piliferum constitutes a distinct lineage. Analyses including Kornmanniaceae recover monophyletic Ulotrichales and Ulvales, whereas analyses omitting the Kornmanniaceae indicate that Ulotrichales is paraphyletic. The structures associated with gamete fusion are conserved within Ulotrichales and Ulvales and perhaps more widely within Chlorophyta.     

谷子和狗尾草核型分析

作者研究了我国谷子(Setaria italica Beauv.)和狗尾草的核型与Giemsa带,两者核型基本相同,均为2n=18=14m+2sm+2st(SAT)。带型亦相近,另外在谷子和狗尾草中都发现有四倍体。     

Orientation of reaction center and antenna chromophores in the photosynthetic membrane of rhodopseudomonas viridis

Whole cells of Rhodopseudomonas viridis were oriented in a magnetic field. The degree of orientation of the cells was determined by using a photoselection technique. In order to deduce the orientation of the antennae and chromophores of the reaction centers with respect to the membrane plane, we performed linear dichroism measurements of absolute spectra and light induced difference spectra linked to states P⁺I and PI^? on oriented cells. These measurements lead to the following conclusions:The antennae bacteriochlorophyll molecular plane is nearly perpendicular to the membrane. The Q_y and Q_x transitions moments of these molecules make respectively angles of 20 and 70°ith the membrane plane. The antenna carotenoid molecules make an angle of 45°ith the membrane.The primary electron donor possesses two transition moments centered respectively at 970 and 850 nm. The 970 nm transition moment is parallel to the membrane plane, the 850 nm transition is tilted out of the plane. Upon photooxidation of this primary electron donor, a monomer-like absorption band appears at 805 nm. Its transition makes an angle smaller than 25° with the membrane. The photooxidation of the dimer also induces an absorption band shift for the two other bacteriochlorophyll molecules of the reaction center. The absorption band shifts of the two bacteriochlorophyll molecules occur in opposite direction.One bacteriopheophytin molecule is photoreduced in state PI^?. This photoreduction induces an absorption band shift for only one bacteriochlorophyll molecule. Finally, the geometry of the dimeric primary donor seems to be affected by the presence of a negative charge in the reaction center.     

Algal colonization in urchin barrens: defense by association during recruitment of the brown alga Agarum cribrosum

We investigated the process whereby juveniles of the kelp Agarum cribrosum escape grazing by the green sea urchin, Strongylocentrotus droebachiensis, on urchin barrens in the rocky subtidal zone in the Mingan Islands, northern Gulf of St. Lawrence. The highest recruitment of juvenile A. cribrosum occurred under the canopy of the large filamentous phaeophyte Desmarestia viridis, where urchin densities were markedly reduced, compared to the surrounding area. This pattern of distribution appeared to be related to the wave-induced sweeping motion of D. viridis, although currents may modify the back and forth motion of the alga by pushing the canopy towards a specific direction, thereby allowing urchins to invade the non-swept areas. The density of juveniles under D. viridis plants increased with plant size and increasing proximity to the holdfast. Living under D. viridis slightly reduced the growth rate of the A. cribrosum juveniles, but this loss in growth was clearly outweighed by the gain in protection from sea urchin grazing. The time scale over which D. viridis provides protection is in the order of months, as D. viridis is an annual alga that disappears in early autumn. This defensive association of juvenile A. cribrosum with D. viridis is possibly a successional step leading to the formation of mature stands of A. cribrosum.     

Response of green alder (Alnus viridis subsp. fruticosa) patch dynamics and plant community composition to fire and regional temperature in north‐western Canada

Aim Feedbacks between climate warming and fire have the potential to alter Arctic and sub‐Arctic vegetation. In this paper we assess the effects and interactions of temperature and wildfire on plant communities across the transition between the Arctic and sub‐Arctic. Location Mackenzie Delta region, Northwest Territories, Canada. Methods We sampled air temperatures, green alder (Alnus viridis ssp. fruticosa) cover, growth, reproduction and age distributions, and overall plant community composition on burned and unburned sites across a latitudinal gradient. Results Mean summer temperature across the study area decreased by 3 °C per degree of increasing latitude (6 °C across the study area). In the northern part of the study area, where seed viability was low, alder was less dominant than at southern sites where seed viability was high. The age structure of alder populations across the temperature gradient was highly variable, except in the northern part of the forest–tundra transition, where populations were dominated by young individuals. Alder growth and reproduction were significantly greater on burned sites (38–51 years following fire) than on unburned sites. North to south across the temperature gradient, vegetation changed from a community dominated by dwarf shrubs and fruticose lichens to one characterized by black spruce (Picea mariana), alder and willows (Salix spp.). Regardless of the position along the temperature gradient, burned sites were dominated by tall shrubs. Main conclusions Temperature limitation of alder abundance and repro‐duction, combined with evidence of recent recruitment on unburned sites, indicates that alder is likely to respond to increased temperature. Elevated alder growth and reproduction on burned sites shows that wildfire also has an important influence on alder population dynamics. The magnitude of alder’s response to fire, combined with observations that burns at the southern margin of the low Arctic are shrub dominated, suggest that increases in the frequency of wildfire have the potential to alter northern vegetation on decadal scales. By creating new seedbeds, fire provides opportunities for colonization that may facilitate the northward movement of tall shrubs. Feedbacks between the global climate system and low Arctic vegetation make understanding the long‐term impact of increasing fire frequency critical to predicting the response of northern ecosystems to global change.     

Maternal and developmental toxicity of ayahuasca in Wistar rats

INTRODUCTION: Ayahuasca is a psychotropic plant beverage initially used by shamans throughout the Amazon region during traditional religious cult. In recent years, ayahuasca has also been used in ceremonies of a number of modern syncretic religious groups, including pregnant women. However, no documented study has been performed to evaluate the risk of developmental toxicity of ayahuasca. METHODS: In the present work, maternal and developmental toxicity was evaluated in Wistar rats. Ayahuasca was administered to pregnant rats in three different doses [the equivalent typical dose (TD) administered to humans, five‐fold TD and 10‐fold TD] during the gestational period (6–20 days). RESULTS: Dams treated with the highest ayahuasca dose showed maternal toxicity with decrease of weight gain and food intake. Visceral fetal findings were observed in all treatment groups. Skeletal findings were observed in the intermediate‐ and high‐dose groups. The fetuses deriving from the highest dose group also presented a decrease in body weight. CONCLUSIONS: From these results, it is possible to conclude that there is a risk of maternal and developmental toxicity following ayahuasca exposure and that the level of toxicity appears to be dose‐dependent. Birth Defects Res (Part B) 89:207–212, 2010. © 2010 Wiley‐Liss, Inc.     

Catalytic properties of endo-1,3-β-D-glucanase from the Vietnamese edible mussel Perna viridis

A β-1,3-glucanase with a molecular mass of 33 kDa was isolated in the homogeneous state from a crystalline stalk of the commercially available Vietnamese edible mussel Perna viridis. It hydrolyzes β-1,3-bonds in glucans and is capable of catalyzing the transglycosylation reaction. The β-1,3-glucanase has a K _m value of 0.3 mg/ml for the hydrolysis of laminaran and shows a maximum activity in the pH range from 4 to 6.5 and at 45°C. Its half-inactivation time is 180 min at 45°C and 20 min at 50°C. The enzyme was ascribed to glucan-endo-(1 → 3)-β-D-glucosidases (EC 3.2.1.39). The enzyme could be used in the structure determination of β-1,3-glucans and enzymatic synthesis of new carbohydrate-containing compounds.     

Monophasic kinetics of electron donation from stromal reductants in unicellular halophytic alga Tetraselmis viridis: Relation of the function to characteristic structure of chloroplast membrane system

Redox conversions of P700, the primary donor of photosystem I (PSI), were investigated in cells of a halophytic alga Tetraselmis viridis Rouch. under irradiation with white light pulses that excite both photosystems of the chloroplast and with far-red light initiating photochemical reactions in PSI only. The P700⁺ dark reduction after irradiation with 50-ms pulse of white light comprised three kinetic components. The half-decay times and relative contributions of the fast, middle, and slow components were 38 ms (49%), 295 ms (26%), and 1690 ms (23%), respectively. The treatment with diuron, known to block electron transport between the photosystems, eliminated the middle exponential term having the half-decay time of 295 ms. After irradiation with far-red light, the kinetics of P700⁺ dark reduction comprised only two components with half-deacy times of 980 ms (72%) and 78 ms (31%). The component with a decay halftime of about 100 ms was fully inhibited after treating the cells with antimycin A, a specific inhibitor of ferredoxin-dependent cyclic electron flow around PSI. In addition, this kinetic component was strongly suppressed by methyl viologen known to inhibit this alternative pathway of electron transport. Both aforementioned reagents had no effect on the slow component of P700⁺ reduction; this component remained monophasic. Unlike higher plant chloroplasts, the chloroplasts of Tetraselmis viridis contained no stacked grana. Based on inhibitor analysis and electron microscopy data, it was concluded that the slow component of P700⁺ reduction in the cells of halophytic microalga reflects the electron donation to PSI from reductants localized in the chloroplast stroma. The monophasic kinetics of this process in the halophytic microalga, compared to the biphasic kinetic pattern in higher plants, is related to the lack of stacked grana in Tetraselmis viridis cells.     

Cues from the predator crab Thalamita danae fed different prey can affect scope for growth in the prey mussel Perna viridis

Clearance rate (CR), absorption efficiency (AE), respiration rate, excretion rate and scope for growth (SFG) were investigated in the green-lipped mussel Perna viridis upon exposure to predatory crabs, Thalamita danae, that had been either starved or maintained on diets with P. viridis or shrimp tissue. The CR and SFG were significantly lower when the mussels were exposed to starved T. danae or those fed with mussels. The differences were observed immediately after the mussels were exposed to the cues (Day 0) and 7 days later. The AE, however, was significantly different among treatments on Day 0, with the highest efficiency being obtained for mussels exposed to crabs maintained on shrimp and followed by the control without any predator cues. Results showed that P. viridis was able to discriminate between predators on different diets and adjust physiological responses according to the level of perceived risk, with growth reduced at higher risks.