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1

Digitale Medien

Excitation energy flow at 77 K in the photosynthetic apparatus of overwintering evergreens (2003)

GILMORE, A. M. ; MATSUBARA, S. ; BALL, M. C. ; [weitere]

Oxford, UK : Blackwell Science Ltd

Plant, cell & environment 26 (2003), S. 0

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ISSN: 1365-3040

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: The flow of excitation energy from the antennae to photosynthetic reaction centre complexes at 77 K was studied in leaves of two evergreen species, namely, snow gum (Eucalyptus pauciflora Sieb. ex Spreng.) and a hemiparasitic mistletoe (Amyema miquelii, Lehm. ex Miq.). The leaves that were naturally acclimated to winter conditions of freezing temperatures and high irradiance displayed the recently discovered cold-hard-band or CHB feature of the chlorophyll a fluorescence spectra (Gilmore & Ball, Proc. Nat. Acad. Sci. USA 97:11098–11101, 2000). A streak-camera-spectrograph was used and the double convolution integral method for global analysis was applied to simultaneously acquire and simulate, respectively, the time- and wavelength-dependence of all major chlorophyll a components (Gilmore et al. Phil. Trans. Roy. Soc. B-London 355:1371–1384, 2000). The CHB coincided with changed amplitudes and decreased excited state lifetimes for the main F685 nm and F695 nm emission bands from the photosystem II (PSII) core-inner-antenna. The CHB dissipates energy as heat separate from PSII while also reducing the PSII quantum yield by competing for both photon absorption and antenna excitation. The CHB did not correlate with changes in the decay kinetics of the PSI antenna F740 nm band. The spectral-kinetic features of the altered energy flow were similar in the unrelated evergreen species. These results are consistent with a functional association between the CHB, PSII energy dissipation and protective storage of chlorophyll in overwintering evergreens.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01026.x

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2

Digitale Medien

Nocturnally retained zeaxanthin does not remain engaged in a state primed for energy dissipation during the summer in two Yucca species growing in the Mojave Desert (2002)

Barker, D. H. ; Adams, W. W. ; Demmig-Adams, B. ; [weitere]

Oxford, UK : Blackwell Science, Ltd

Plant, cell & environment 25 (2002), S. 0

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ISSN: 1365-3040

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie

Notizen: Differently oriented leaves of Yucca schidigera and Yucca brevifolia were characterized in the Mojave Desert with respect to photosystem II and xanthophyll cycle activity during three different seasons, including the hot and dry summer, the relatively cold winter, and the mild spring season. Photosynthetic utilization of a high percentage of the light absorbed in PSII was observed in all leaves only during the spring, whereas very high levels of photoprotective, thermal energy dissipation were employed both in the summer and the winter season in all exposed leaves of both species. Both during the summer and the winter season, when energy dissipation levels were high diurnally, xanthophyll cycle pools (relative to either Chl or other carotenoids) were higher relative to the spring, and a nocturnal retention of high levels of zeaxanthin and antheraxanthin (Z + A) occurred in all exposed leaves of both species. Although this nocturnal retention of Z + A was associated with nocturnal maintenance of a low PSII efficiency (Fv/Fm) on a cold winter night, pre-dawn Fv/Fm was high in (Z + A)-retaining leaves following a warm summer night. This indicates nocturnal engagement of Z + A in a state primed for energy dissipation throughout the cold winter night – while high levels of retained Z + A were not engaged for energy dissipation prior to sunrise on a warm summer morning. Possible mechanisms for a lack of sustained engagement of retained Z + A for energy dissipation at elevated temperatures are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.0016-8025.2001.00803.x

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3

Digitale Medien

Trichodina murmanica (Ciliophora) and Gyrodactylus pleuronecti (Monogenea) parasitizing hatchery-reared winter flounder, Pseudopleuronectes americanus (Walbaum): effects on host growth and assessment of parasite interaction (2002)

Barker, D E ; Cone, D K ; Burt, M D B

Oxford UK : Blackwell Science Ltd.

Journal of fish diseases 25 (2002), S. 0

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ISSN: 1365-2761

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Biologie , Medizin

Notizen: Winter flounder, Pseudopleuronectes americanus, caught in Passamaquoddy Bay, New Brunswick, Canada, and held captive under crowded conditions, developed mixed infections of Trichodina murmanica Polyanski, 1955 (Ciliophora) and Gyrodactylus pleuronecti Cone, 1981 (Monogenea). A protocol involving sequential sieving was used to separate the two species of parasites and produce viable experimental baths. Replicate groups of juvenile, hatchery-reared flounder received one of the following treatments: mixed bath of G. pleuronecti and T. murmanica, bath of G. pleuronecti, bath of T. murmanica or parasite-free (controls). The abundance of both parasites correlated negatively with condition factor of the flounder (r=−0.354, P 〈 0.001 for Trichodina; r=–0.205, P 〈 0.05 for Gyrodactylus). During the periods of peak parasite abundance (1–2 weeks postinfection), the effect of the two parasite species was additive, as mean condition factor and the percentage change in weight were significantly lower (ANOVA, P 〈 0.05) among fish with mixed infections compared to single infections or controls. The most common signs of tissue pathology were increased density of epidermal mucous cells on the fins and macrovesicular lipidosis of the hepatocytes. After a significant decline in parasite infrapopulations (3 weeks postinfection), infected fish resumed normal growth, indicating the observed effects were somewhat reversible.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-2761.2002.00341.x

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4

Digitale Medien

The DNA sequence and analysis of human chromosome 6 (2003)

Palmer, S. A. ; Sims, S. K. ; Edwards, C. A. ; [weitere]

[s.l.] : Macmillian Magazines Ltd.

Nature 425 (2003), S. 805-811

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] Chromosome 6 is a metacentric chromosome that constitutes about 6% of the human genome. The finished sequence comprises 166,880,988 base pairs, representing the largest chromosome sequenced so far. The entire sequence has been subjected to high-quality manual annotation, resulting in the ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/nature02055

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5

Digitale Medien

Dynamic measurements of initiation toughness at high loading rates (1988)

Dally, J. W. ; Barker, D. B.

Springer

Experimental mechanics 28 (1988), S. 298-303

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ISSN: 1741-2765

Quelle: Springer Online Journal Archives 1860-2000

Thema: Maschinenbau

Notizen: Abstract An experimental method is described for measuring the dynamic initiation toughness of a sharp stationary crack. A plane specimen is utilized which consists of a central region 50-mm wide and 200-mm long with integral dog-bone ends. The loading is accomplished by the detonation of four small explosive charges which produce two tensile stress waves upon reflection from the dog-bone ends. The stress waves meet at the midpoint of the specimen and reinforce to produce a relatively large, uniformly stressed region with a very high loading rate. The crack is positioned at the midpoint of the specimen at the location where the reinforcing tensile stress waves meet. A series of photoelastic experiments were conducted using Homalite 100 as the model material to observe, in a full-field view, the arrival of the dilatational waves, the subsequent development of the stress field at the tip of the stationary crack and the initiation of the crack. The isochromatic fringe pattern was also used to determine the instantaneous value of the stress-intensity factorK(t) after the characteristic fringe loops developed in the region near the crack tip. Finally,K(t) was measured using a single strain gage positioned and oriented so that its signal output was proportional toK(t) and independent of the next two higher order terms in the series representation of the strain field. A method was developed to determine the instant of initiation from the strain-time trace. Results obtained from the photoelastic and strain measurements of the dynamic-initiation toughnessK ID were consistently higher than the static value ofK IC .

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF02329026

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