| 1. |
- Gough, Simon, et al.
(författare)
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A new method for isolating physiologically active Mg-protoporphyrin
- 2007
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Ingår i: Plant Physiology and Biochemistry. - : Elsevier BV. - 1873-2690 .- 0981-9428. ; 45:12, s. 932-936
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Tidskriftsartikel (refereegranskat)abstract
- Mg-protoporphyrin monomethyl ester (MPE) is a biosynthetic intermediate of chlorophyll and converted by MPE cyclase to protochlorophyllide. Limited availability of MPE has so far hampered cyclase research. In a new, simplified, method MPE was prepared from freeze dried bchE mutant Rhodobacter capsulatus DB575 cells by extraction with acetone/H2O/25% NH3. Isolated MPE was identified by absorption and fluorescence spectroscopy, and its purity was analyzed by HPLC. The extracted MPE was dried and redissolved in buffered DMSO and its substrate activity is shown by enzymatic cyclase assays. A linear time course was observed for MPE conversion to protochlorophyllide by enzymes from barley etioplasts. Our innovation of freeze drying the R. capsulatus cells before extraction provides a high yield method for MPE, which is significantly faster and more reproducible than previous extraction methods.
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| 2. |
- Gough, Simon P, et al.
(författare)
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A new method for isolating physiologically active Mg-protoporphyrin monomethyl ester, the substrate of the cyclase enzyme of the chlorophyll biosynthetic pathway.
- 2007
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Ingår i: Plant Physiology and Biochemistry. - : Elsevier BV. - 0981-9428. ; 45:12, s. 932-6
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Tidskriftsartikel (refereegranskat)abstract
- Mg-protoporphyrin monomethyl ester (MPE) is a biosynthetic intermediate of chlorophyll and converted by MPE cyclase to protochlorophyllide. Limited availability of MPE has so far hampered cyclase research. In a new, simplified, method MPE was prepared from freeze dried bchE mutant Rhodobacter capsulatus DB575 cells by extraction with acetone/H2O/25% NH3. Isolated MPE was identified by absorption and fluorescence spectroscopy, and its purity was analyzed by HPLC. The extracted MPE was dried and redissolved in buffered DMSO and its substrate activity is shown by enzymatic cyclase assays. A linear time course was observed for MPE conversion to protochlorophyllide by enzymes from barley etioplasts. Our innovation of freeze drying the R. capsulatus cells before extraction provides a high yield method for MPE, which is significantly faster and more reproducible than previous extraction methods.
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| 3. |
- Stenbaek, Anne, et al.
(författare)
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NADPH-dependent thioredoxin reductase and 2-Cys peroxiredoxins are needed for the protection of Mg–protoporphyrin monomethyl ester cyclase
- 2008
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Ingår i: FEBS Letters. - : Wiley. - 1873-3468 .- 0014-5793. ; 582:18, s. 2773-2778
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The chloroplast-localized NADPH-dependent thioredoxin reductase (NTRC) has been found to be able to reduce hydrogen peroxide scavenging 2-Cys peroxiredoxins. We show that the Arabidopsis ntrc mutant is perturbed in chlorophyll biosynthesis and accumulate intermediates preceding protochlorophyllide formation. A specific involvement of NTRC during biosynthesis of protochlorophyllide is indicated from in vitro aerobic cyclase assays in which the conversion of Mg–protoporhyrin monomethyl ester into protochlorophyllide is stimulated by addition of the NTRC/2-Cys peroxiredoxin system. These findings support the hypothesis that this NADPH-dependent hydrogen peroxide scavenging system is particularly important during periods with limited reducing power from photosynthesis, e.g. under chloroplast biogenesis.
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| 4. |
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| 5. |
- Bernhold, Andreas, et al.
(författare)
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Resistance to Gremmeniella abietina (European race, large tree type) in introduced Pinus contorta and native Pinus sylvestris in Sweden
- 2009
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Ingår i: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 39, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- To study the resistance of Pinus contorta Dougl. ex Loud. var. latifolia Engelm. ex Watts to large tree type (LTT) Gremmeniella abietina (Lagerberg) Morelet of the European race, seedlings of P. contorta and Pinus sylvestris L. were planted in gaps of an infected 40-year-old P. sylvestris stand in 2005 and assessed for symptoms in 2006-2007. In 2007, 45% and 32% of the P. contorta and P. sylvestris seedlings were infected, respectively. However, mortality was lower and recovery was better in the P. contorta seedlings. The mean infection length on surviving seedlings was significantly shorter in P. contorta ( 4 cm) compared with P. sylvestris ( 10 cm), and 47% of the P. contorta seedlings had developed new leader shoots in 2007 compared with 19% of the P. sylvestris seedlings. Histopathological examinations of the transition zone of infected shoots showed that P. contorta, as well as P. sylvestris, produced ligno-suberized boundaries extending from healthy needle bases transversally across the shoots. Together with areas of phenol-filled cells, these boundaries completed the compartmentalization of the invaded outermost parts of a majority of the infected seedlings. Our results indicate that P. contorta is more resistant to LTT G. abietina than P. sylvestris.
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| 6. |
- Hansson, Andreas, et al.
(författare)
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Chlorophyll limitation in plants remodels and balances the photosynthetic apparatus by changing the accumulation of photosystems I and II through two different approaches.
- 2009
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 135:2, s. 214-228
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Tidskriftsartikel (refereegranskat)abstract
- Arabidopsis plants with a reduced expression of CHL27 (chl27), an enzyme (EC 1.14.13.81) required for the synthesis of Pchlide, are chlorotic and have a Chl a/b ratio two times higher than wild-type (WT). Knockdown plants transformed with a construct constitutively expressing CHL27 recovered regarding Chl level, a/b ratio and 77K fluorescence. A negative correlation was found between total Chl and Chl a/b ratio in the examined plants. The chl27 plants fail to assemble WT amounts of complete PSI and PSII, leading to an elevated PSII/PSI ratio. The PSI remaining in chl27 is fully functional with a quantum yield higher than for WT. Despite a severe reduction of photosystem II antennae protein (LHCII) and an increased proportion of stroma lammella, the chl27 plants are able to perform state transitions. No major differences were found regarding PSII quantum yield, qN and 1 - qp whereas non-photochemical quenching was decreased by a factor two in chl27 plants. The PSII quantum yield for dark-adapted plants and plants given 10 min recovery after high light treatment were similar for both WT and chl27 showing that chl27 plants are not more susceptible to photoinhibition than WT. Taken together the plant manage to acclimate and to balance the two photosystems well even when it is severely limited in Chl. The way to achieve this differs for the two photosystems: regarding PSI a general reduction of core and antenna subunits occurs with no apparent change in the antenna composition; whereas for PSII there is a preferential loss of antenna proteins.
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| 7. |
- Hansson, Andreas, 1984-
(författare)
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Increasing the storage capacity of Recursive Auto-associative Memory by segmenting data
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recursive Auto-associative Memory (RAAM) has been proposed as a connectionist solution for all structured representations. However, it fails to scale up to representing long sequences of data. In order to overcome this, a number of different architectures and representations have been proposed. It is here argued that part of the problem of, and solution to, storing long sequences in RAAM is data representation. It is proposed that by dividing the sequences to be stored into smaller segments that are individually compressed the problem of storing long sequences is reduced.This licentiate thesis investigates which different strategies there are for segmenting the sequences. Several segmentation strategies are identified and organized into a taxonomy. Also, a number of experiments based on the identified segmentation strategies that aims to clarify if, and how, segmentation affect the storage capacity of RAAM are performed.The results of the experiments show that the probability that a sequence of a specific length stored in RAAM can be correctly recalled is increased by up to 30% when dividing the sequence into segments. The performance increase is explained by that segmentation reduces the depth at which a symbol is encoded in RAAM which reduces a cumulative error effect during decoding of the symbols.
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| 8. |
- Hansson, Andreas, et al.
(författare)
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Using Segmentation to Control the Retrieval of Data
- 2006
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Ingår i: The 2006 IEEE International Joint Conference on Neural Network Proceedings. - : IEEE. - 0780394909 - 9780780394902 ; , s. 1764-1769
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- One problem when storing sequential data using recurrent neural networks is that it is hard to preserve long term dependencies. Only the most recently stored data tend to be accurately recalled. One approach for reducing this recency effect has been to divide the data into segments and store the segments separately. This approach has provided promising results in prediction and classification domains. This paper analyzes in what way recall of the stored data is affected by segmentation. It is concluded that segmentation enables the control of which data that can be recalled. The problem of preserving long term dependencies in recurrent neural networks can therefore be reduced.
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| 9. |
- Hansson, Lena, 1975-
(författare)
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Enligt fysiken eller enligt mig själv? : Gymnasieelever, fysiken och grundantaganden om världen
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I avhandlingen studeras elevers grundantaganden om världen, samt de grundantaganden som eleverna förknippar med fysiken. Det är utifrån de grundantaganden vi gör om hur världen är beskaffad som vi försöker tolka och förstå nya fenomen och företeelser vi möter, t.ex. i den naturvetenskapliga undervisningen. I avhandlingen ligger intresset primärt på grundantaganden som vanligtvis tas för givna i naturvetenskapen samt sådana som är av intresse för relationen mellan naturvetenskap och religion. För de empiriska studierna har ett specifikt område, nämligen universums uppkomst och utveckling samt existentiella frågor relaterade till detta, valts som ram för elevernas resonemang. Avhandlingen bygger på två studier. I den första studeras elevers skriftliga svar och uttalanden under intervjuer och i den andra studeras elevers gruppdiskussioner. Eleverna som deltar i de båda studierna går alla det tredje året på gymnasiet och läser kursen Fysik B.Resultaten visar att det finns elever som beskriver sin egen och fysikens syn på olika sätt. Detta gäller såväl frågor om universums uppkomst och utveckling som frågor om t.ex. relationen mellan naturvetenskap och religion. Resultaten visar vidare att de grundantaganden som vanligtvis underförstås i fysiken inte med självklarhet associeras med fysiken av eleverna. Detta kan göra det svårt för dem att förstå resonemang och modeller i fysiken. Resultaten visar vidare att det är vanligt att elever associerar scientistiska synsätt med fysiken. Scientism innebär att man menar att ingenting utom det som är åtkomligt för naturvetenskapen existerar. Detta uteslutet möjligheten att andra möjliga dimensioner av verkligheten än den materiella existerar. Att förknippa fysiken med antaganden som inte av nödvändighet måste förknippas med fysiken (t.ex. scientistiska synsätt) kan göra att elever, som inte själva delar dessa antaganden, får svårare att identifiera sig med fysiken och kanske t.o.m. väljer bort studier i fysik när möjlighet ges.
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| 10. |
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