OPUS 4 | Search

Rezension zu: Thomas Fischer (Hg.), Die Krise des 3. Jahrhunderts n. Chr. und das Gallische Sonderreich. Akten des Interdisziplinären Kolloquiums Xanten 26. bis 28. Februar 2009, Zakmira 8 (Wiesbaden 2012) (2013)

Erich Kettenhofen

Il tardoantico: declino o trasformazione? (2013)

Alberto Giudice

Premessa: In precedenti saggi ho già evidenziato, analizzando il commercio a lungo raggio e interessandomi del dibattito storiografico sul tardoantico , come l’analisi dei dati archeologici consenta di individuare molte caratteristiche del c.d. "basso impero" e le trasformazioni che avvengono in questo periodo. In questo saggio si giunge ad un ulteriore approfondimento rispetto ai precedenti studi e si sono prese in considerazione le modalità insediative che si susseguono nel periodo compreso tra il IV ed il VII secolo d.C., in modo da delineare lo status quaestionis, ricostruire le dinamiche storiche che hanno portato alle modifiche e comprendere se questa epoca può essere considerata di declino oppure no. Per fare questo si è scelto un approccio metodologico che ha preferito analizzare i dati archeologici di aree cardine dell’Impero roma no d’occidente quali l’Italia, la penisola Iberica e la Gallia, per verificare se vi siano dinamiche comuni indicanti le possibili contingenze che hanno portato alla modifica dell’assetto insediativo nelle campagne. In questo modo si è anche capito se le trasformazioni che si sono verificate nel periodo analizzato posso no essere immesse nella categoria del declino o se, al contrario, i cambiamenti rappresentano una risposta attiva al contesto storico di appartenenza. Si presenteranno, quindi, prima i dati archeologici e poi si attuerà, in sede di conclusioni, l’analisi degli stessi per comprendere, anche alla luce delle fonti letterarie, i fenomeni che si sono verificati nel peri odo compreso tra il IV ed il VII secolo

Function of plant photosystem II subunits in photoprotection (2013)

Laura-Varenne Wilk

Plants absorb sunlight via photosynthetic pigments and convert light energy intochemical energy in the process of photosynthesis. These pigments are mainly bound to antenna protein complexes that funnel the excitation energy to the photosynthetic reaction centres. The peripheral antenna of plant photosystem II (PSII) consists of the major light-harvesting complex of PSII (LHC-II) and the minor LHCs CP29, CP26 and CP24. Light intensity can change frequently and plants need to adapt to high-light conditions in order to avoid photodamage. When more photons are absorbed than can be utilised by the photosynthetic machinery, excessive excitation energy is dissipated as heat by short-term adaptation processes collectively known as non-photochemical quenching (NPQ). A decrease in PSII antenna chlorophyll (Chl) fluorescence yield and a reduction in the average Chl fluorescence lifetime are associated with NPQ. The main component of NPQ is the so-called energy-dependent quenching (qE), and it is triggered by the rapid drop in thylakoid lumenal pH resulting from the plant’s photosynthetic activity. This process is thought to take place at the PSII antenna complexes, which therefore not only capture and transfer light energy but are also involved in balancing the energy flow. The decrease in lumenal pH acivates the enzyme violaxanthin de-epoxidase (VDE), which converts the xanthophyll violaxanthin (Vio) into zeaxanthin (Zea) in the xanthophyll cycle. In addition, the PSII subunit PsbS was discovered to be essential for qE by screening qE-deficient Arabidopsis thaliana mutants. This membrane protein is considered a member of the LHC superfamily, which also includes LHC-II and the minor LHCs. Previous studies on PsbS isolated either from native source or refolded in vitro have produced inconsistent results on its pigment binding capacity. Interestingly, a pH-dependent change in the quaternary structure of PsbS under high light conditions has been reported. This observed dimer-tomonomer transition very likely follows the protonation of lumenal glutamates upon the drop in pH and is accompanied by a change in PSII supercomplex localisation. PsbS dimers are preferentially found in association with the PSII core, whereas PsbS monomers co-localise with LHC-II.Despite the identification of !pH, Zea and PsbS as key players in qE, both the nature of the quencher(s) as well as the underlying molecular mechanism leading to excess energy dissipation still remain unknown. Several models have been put forward to explain the reversible switch in the antenna from an energy-transmitting to a quenched state. Proposals include a simple pigment exchange of Vio for Zea, and aggregation or an internal conformational change of LHC-II. Charge transfer (CT)quenching in the minor LHCs or quenching by carotenoid dark state (Car S1)-Chl interactions have also been suggested. However, none of these qE models has so far been capable of accommodating all the physiological observations and available experimental data. Most importantly, the function of PsbS remains an enigma. A recent qE model suggested that monomerisation of PsbS enables the protein to transiently bind a carotenoid and form a quenching unit with a Chl of a PSII LHC. In view of the various proposed qE mechanisms, this thesis aimed at understanding the interplay of the different qE components and the contribution of the PSII subunits LHC-II, the minor LHCs and PsbS to qE. The initial approach was to investigate the properties of the PSII subunits in the most simple in vitro model system, namely in detergent solution. For this purpose, LHC-II was isolated either from native source or refolded from recombinantly produced protein. Investigation of the minor LHCs and PsbS required heterologous expression and refolding. In addition, experiments were performed on aggregated LHC-II. Aggregates of LHC-II have been used as a popular model system for qE because they exhibit highly quenched Chl fluorescence. At the final stage of this doctoral work, a more sophisticated model system to approximate the thylakoid membrane was developed by reconstitution of the PSII subunits LHC-II and PsbS into liposomes. This system not only allowed for investigation of these membrane proteins in their native environment, but also for mimicking the xanthophyll cycle by distribution of Zea within the membrane as well as !pH by outside buffer exchange. The role of Zea in qE was first investigated with detergent solubilised antenna proteins. The requirement of this xanthophyll for qE is well-known, but the specific contribution to the molecular quenching mechansim is unclear. Previous work had shown that replacement of Vio for Zea in LHC-II was not sufficient to induce Chl fluorescence quenching in Zea-LHC-II, as suggested by the so-called molecular gearshift mechanism. However, by means of selective two-photon excitation spectroscopy, an increase in electronic interactions between Car S1 and Chls was observed for LHC-II upon lowering the pH of the detergent buffer. Electronic Car S1-Chl coupling became even stronger when Zea-LHC-II was probed. The extent of Car S1-Chl coupling correlated directly with the extent of Chl fluorescence quenching, in a similar way as observed previously in live plants under high-light conditions. However, very similar results were obtained with LHC-II aggregates. This implied that the increase in electronic interactions and fluorescence quenching was independent of Zea and low pH. Further experiments on aggregates of LHC-II Chl mutants indicated that the targeted pigments were also not essential for the observed effects. It is proposed that the same molecular mechanism causes an increase in electronic Car S1-Chl interactions and Chl fluorescence quenching in Zea-LHC-II at low pH as well as in aggregated LHC-II. Most likely, surface exposed pigments form random quenching centres in both cases. On the other hand, it was possible that Zea could act as a direct quencher of excess excitation energy in the minor LHCs. However, enrichment of refolded CP29, CP26 and CP24 with Zea did not lead to a change in the Chl excited state lifetime. Formation of a carotenoid radical cation, previously implied in CT quenching, was also not observed, although artificial generation of such a radical cation was principally possible as shown for CP29. During the course of this work, a study reporting the formation of Zea radical cations in minor LHCs was published. Therefore, Zea-enriched minor LHCs were again investigated on the experimental apparatus used in the reported study. Indeed, the presence of at least one carotenoid radical cation for each minor complex was detected. It is suggested that either the preparation method of incubating the refolded minor LHCs with Zea in contrast to refolding the complexes with only Zea and lutein causes the observed differences or that the observed spectral radical cation signatures are due to experimental artifacts. While the experiments with LHC-II and the minor LHCs gave useful insights into the putative qE mechanism, the quencher site and the mode of action of Zea could still not be unambiguously identified. Most importantly, these studies could not explain the function of the qE keyplayer PsbS. Therefore, the focus of the work was shifted to PsbS protein production, purification and characterisation. In view of inconsistent reports on the pigment binding capacity of this PSII subunit, refolding trials with and without photosynthetic pigments were conducted. The formation of a specific pigmentprotein complex typical for other LHCs was not observed and neither was the earlier reported “activation” of Zea for qE by binding to this protein. Nevertheless, PsbS refolded without pigments displayed secondary structure content in agreement with previous studies, indicating pigment-independent folding. Reconstitution of pigmentfree, refolded PsbS into liposomes confirmed that the protein is stable in the absence of pigments. Zea distributed in PsbS-containing liposomes also showed no spectral alteration that would indicate its “activation”. With the ability to reconstitute PsbS, it was then possible to proceed to modelling qE in a proteoliposome system. For this purpose, PsbS was co-reconstituted with LHC-II, which has been reported to interact with PsbS. One-photon excitation (OPE) and two-photon excitation (TPE) spectroscopy measurements were performed on LHC-II- and LHC-II/PsbS-containing liposomes. This enabled both quantification of Chl fluorescence quenching as well as determination of the extent of electronic Car S1-Chl interactions. The effect of Zea was investigated by incorporating it in the proteoliposome membrane. It was shown that Zea alone was not able to induce significant Chl fluorescence quenching when only LHC-II was present. However, when LHC-II and PsbS were co-reconstituted, pronounced Chl fluorescence quenching and an increase in electronic Car S1-Chl interactions were observed and both effects were enhanced when Zea was present. Western blot analysis indicated the presence of a LHC-II/PsbS-heterodimer in these proteoliposomes. In addition to the OPE and TPE measurements, the average Chl fluorescence lifetime was determined in detergent-free buffer at neutral pH and directly after buffer exchange to low pH. No significant changes in the average lifetime were observed for LHC-II proteoliposomes when either Zea was present or after exchange for low pH buffer. This indicated that Zea alone cannot act as a direct quencher, which concurs with the OPE measurements. Moreover, the complex was also properly reconstituted as no aggregation or significant Chl fluorescence quenching were observed. The average lifetime was not significantly affected in LHC-II/PsbS-proteoliposomes, independent of Zea or pH. However, a shortlived component in the presence of a long-lived component was not resolvable with the time resolution of the fluorescence lifetime apparatus. Implications for qE model systems and the in vivo quenching mechanism are discussed based on the experiments in detergent solution, on LHC-II aggregates and with the proteoliposome model system.

Limonium hyblaeum (Plumbaginaceae), a cushion plant invading coastal southern Australia (2013)

Robert F. Parsons

The Sicilian endemic herbaceous perennial plant Limonium hyblaeum (family Plumbaginaceae) is rapidly becoming a serious weed in South Australia and Victoria, where it invades saltmarshes and rocky coastal sites exposed to salt spray. It has small, light seeds that float and remain viable in sea water and which can also be dispersed readily by wind, animals and vehicles. It can form dense, extensive mats and buds sprouting from rhizomes allow encroachment into dense native vegetation. It seems certain to be apomictic and is readily able to become dominant. Forming dense, compact cushions which accumulate large amounts of fibrous peat, Limonium hyblaeum is the first cushion plant to become naturalized in Australia; the importance of the cushion habit as an adaptation to salt spray is under-appreciated. Some control measures for Limonium hyblaeum have begun in Victoria, but much remains to be done there and in the other southern Australian states; a ban on the sale of the species by nurseries is urgently required.

Replacement of Cakile edentula with Cakile maritima in New South Wales and on Lord Howe Island (2013)

Kevin Mills

Two species of Cakile (Brassicaceae) have been introduced to Australia and the genus has been a common feature on the beaches of NSW for over 130 years; Cakile edentula has been present for at least 148 years (in NSW since about 1870), while Cakile maritima arrived approximately 114 years ago, (in NSW since about 1969). Collections at CANB and NSW confirm that since around 1970 plants more like Cakile maritima have almost entirely replaced Cakile edentula along the NSW coast. A similar phenomenon is reported for Lord Howe Island.

Upland wetlands in the Namoi Catchment: mapping distribution and disturbance classes of fens, bogs and lagoons (2013)

John T. Hunter

To assist with planning and conservation strategies, mapping of wetlands above 700 m elevation across the Namoi Catchment (east of Tamworth) was undertaken. The number of hectares of each type within this high-elevation region, the area currently in conservation reserves and the status of these remnants was assessed. 1 001 wetlands were mapped and allocated to three wetland types (fens, bogs and lagoons) and six disturbance groups (based on agricultural clearing and presence of dams). Total wetlands cover was 4 490 ha, of which fens were the most common, followed by bogs and a single lagoon. The smallest wetland was 0.12 ha in size, the largest 113 ha and the average 5 ha. Only 10% of all wetlands were considered to be in near natural state with only 5.5% of all wetland area protected within conservation reserves.

Impact of broom, Cytisus scoparius (Fabaceae), in naturally treeless sub-alpine frost-hollow vegetation communities at the Barrington Tops, south-eastern Australia (2013)

John R. Hosking Mellesa Schroder Bruce McCorkell

The exotic shrub Cytisus scoparius (L.) Link (family Fabaceae), known as broom, is having a major impact on native vegetation in naturally treeless sub-alpine frost-hollow areas (c. 32o 01’ 37” S, 151o 26’ 12” E’, 1440 m elevation) at the Barrington Tops, New South Wales, in south-eastern Australia. This vegetation is of limited extent and has significant biogeographical and ecological importance. Nine paired 10 m line transects were compared, with one of the pair in areas of almost 100% Cytisus scoparius and the other in adjacent areas without Cytisus scoparius. Results were compared with species recorded from this area in the 1930s. There are obvious differences in native vegetation in areas with and without Cytisus scoparius. On average there were 5.1 (range 2–10) species per 10 m in areas of almost 100% Cytisus scoparius cover and 17.0 (12–25) species per 10 m in areas adjacent to infested areas but without Cytisus scoparius. Other than Cytisus scoparius, the area surveyed had little in the way of exotic species and these were only present at low densities. Native species present in 2008 are similar to those recorded in the 1930s; there were no records of Cytisus scoparius in the area in the 1930s. The study suggests that control of Cytisus scoparius in naturally treeless areas at the Barrington Tops should be a priority to prevent a decline in the distribution and abundance of many plant species, many of which only occur in treeless areas of the Barrington Tops.

Adventures, hardship and a scientific legacy: Ludwig Leichhardt’s 1843 journey to Mt Royal in the Hunter Valley, NSW (2013)

Martin Fallding Doug Benson

In January 1843, curiosity for natural history led a young German naturalist, Ludwig Leichhardt, to spend about three weeks exploring Mt Royal on the north of the Hunter Valley, about 70 km north west of Newcastle, New South Wales. This was a sidetrack on his journey from Newcastle, through the Hunter Valley and inland to Moreton Bay (Brisbane) and preceded the journeys for which he was to become famous; his 1844–45 overland journey from Moreton Bay to Port Essington (in Northern Territory) and his disappearance without trace in 1848 attempting to cross Australia. Using his Diary and herbarium records this paper brings together the chronological events of the 29 year old Leichhardt’s journey, the plant and animal species recorded, the specimens collected and his landscape descriptions and compares the 1843 landscape with the area today. Most of it is now in Mount Royal National Park, and part of the Gondwana Rainforest Reserves World Heritage Area. Using Mt Royal as an example of the richness of Leichhardt’s scientific legacy, we draw attention to the existence of a considerable number of Leichhardt’s plant specimens in herbaria in Sydney and Melbourne relating to his early collecting around Sydney and the little-known journey from Newcastle to Moreton Bay. Leichhardt’s visit to Mt Royal provides an insight into a gifted young naturalist coping with some of the hardships of nineteenth century botanical exploration, in a landscape which is easily recognizable and of which much is remarkably little changed since European settlement.

Survival of Casuarina cunninghamiana on a recovering sand-bed stream in the Wollombi Valley of coastal New South Wales (2013)

Fiona Erskine Anita Chalmers Wayne Erskine

The successful management and restoration of riparian corridors in Australia is currently hindered by our poor understanding of the links between hydrology, fluvial geomorphology and plant population dynamics. The aim of the current study was to determine the survival rates of Casuarina cunninghamiana subsp. cunninghamiana Miq. (family Casuarinaceae) on a sand-bed stream in the Wollombi Valley, a tributary of the Hunter River system, in coastal New South Wales (lat 33°02’S; long 151°10’E). A population planted on the banks of Dairy Arm in 1987, as part of river training works, was used to determine the long-term (24-year) survival rate. A bankfull flood in June 2011 provided an opportunity to examine the survival response of seedlings regenerating naturally within the channel. We found that 24% of the seedlings planted on the banks in 1987 had survived to adulthood. The bankfull flood significantly decreased (d.f. = 14; W= - 30; p = 0.0024) median seedling density within the channel from 12 to 2 individuals per 100 m2. Seedling survival varied with height, with seedlings > 15 cm more likely to survive the bankfull flood. The percentage of seedlings partially buried by sediment was significantly higher (d.f. = 14; W = 13; p = 0.016) after flood compared to before flood. Seedling density was positively correlated with the amount of bare ground prior to the flood (r = 0.61; p = 0.02), but this relationship was no longer significant after flood (r = 0.18; p = 0.53). 37% of the seedlings surveyed showed evidence of grazing. Our results confirm that hydrogeomorphic processes associated with a bankfull flood affect the survival of Casuarina cunninghamiana seedlings. The management implications of our findings are discussed in terms of riparian revegetation techniques and the geomorphic recovery of over-widened sand-bed streams.

Reassessment of the invasion history of two species of Cakile (Brassicaceae) in Australia (2013)

Roger D. Cousens Peter K. Ades Mohsen B. Mesgaran Sara Ohadi

In this paper we revisit the invasion history of two species of Cakile in Australia. Cakile edentula subsp. edentula arrived in the mid 19th Century and spread into coastal strandline habitat from the southeast towards the west and to the north; Cakile maritima arrived in the late 19th Century and has replaced Cakile edentula over much of the range. While Cakile edentula is morphologically quite uniform, the great variation within Cakile maritima has confused field ecologists. Using herbarium records we update previous accounts of the spread of the species and report on field surveys that determined their current geographic overlap in Tasmania and in northern New South Wales/southern Queensland. We examine regional morphological variation within Cakile maritima using the national herbaria collections and variation within new population samples. We support previous interpretations that Cakile maritima has been introduced on more than one occasion from morphologically distinct races, resulting in regional variation within Australia and high variability within populations in the south-east. Western Australian populations appear distinct and probably did not initiate those in the east; we consider that eastern populations are likely to be a mix of Cakile maritima subsp. maritima from the Mediterranean and Cakile maritima subsp. integrifolia from Atlantic Europe. Although introgression from Cakile edentula into Cakile maritima cannot be discounted from our results, it is not required to explain the levels of variation in the latter species observed in Australia. Cakile maritima continues to spread southwards in Tasmania and northwards in NSW; in Queenland, a recent occurrence has proliferated in Moreton Bay, spreading slowly to the north but not appreciably southwards.

Refine

Author

Year of publication

Document Type

Language

Has Fulltext

Keywords

Institute

31554 search hits