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F Springer

Publications and source records attributed to F Springer.

7 recordsLinked to original sources
PubMed2006

Excitation of nanoscale vapor bubbles at the surface of gold nanoparticles in water.

Intense nonequilibrium femtosecond laser excitation of gold nanoparticles in water leads to a transient heating of the nanoparticles, which decays via heat transfer to the water phase. It is shown that the water temperature rises to near the critical temperature and the water undergoes an explosive evaporation in the subnanosecond range. The formation of vapor bubbles shows a threshold dependence on laser fluence. The nascent nanoscale vapor bubbles change the heat dissipation drastically. The nanoscale structure is resolved directly with a combination of x-ray scattering methods sensitive to the particle lattice expansion and the change in the water structure factor.

Journal Article↗
PubMed2000

Introduction of polyphosphate as a novel phosphate pool in the chloroplast of transgenic potato plants modifies carbohydrate partitioning.

Potato plants (Solanum tuberosum L., cv. Désirée) were transformed with the polyphosphate kinase gene from Escherichia coli fused to the leader sequence of the ferredoxin oxidoreductase gene (FNR) from Spinacea oleracea under the control of the leaf specific St-LS1 promoter to introduce a novel phosphate pool in the chloroplasts of green tissues. Transgenic plants (cpPPK) in tissue culture developed necrotic lesions in older leaves and showed earlier leaf senescence while greenhouse plants showed no noticeable phenotype. Leaves of cpPPK plants contained less starch but higher concentrations of soluble sugars. The presence of polyphosphate in cpPPK leaves was demonstrated by toluidine blue staining and unambiguously verified and quantified by in vitro 31P-NMR of extracts. Polyphosphate accumulated during leaf development from 0.06 in juvenile leaves to 0.83 mg P g-1 DW in old leaves and had an average chain length of 18 residues in mature leaves. In situ 31P-NMR on small leaf pieces perfused with well-oxygenated medium showed only 0.036 mg P g-1 DW polyphosphate that was, however, greatly increased upon treatment with 50 mM ammonium sulfate at pH 7.3. This phenomenon along with a yield of 0.47 mg P g-1 DW polyphosphate from an extract of the same leaf material suggests that 93% of the polyphosphate pool is immobile. This conclusion is substantiated by the observation that no differences in polyphosphate pool sizes could be discerned between darkened and illuminated leaves, leaves treated with methylviologen or anaerobis and control leaves, treatments causing a change in the pool of ATP available for polyPi synthesis. Results are discussed in the context of the chelating properties of polyphosphates for cations and its consequences for the partitioning of photoassimilate between starch and soluble sugars.

Animals↗
PubMed1999

The influence of alterations in ADP-glucose pyrophosphorylase activities on starch structure and composition in potato tubers.

In order to examine whether alterations in the supply of precursor molecules into the starch biosynthetic pathway affected various characteristics of the starch, starch was isolated from potato (Solanum tuberosum L.) tubers containing reduced amounts of the enzyme ADP-glucose pyrophosphorylase (AGPase). It was found that although the type of crystalline polymorph in the starch was not altered, the amylose content was severely reduced. In addition, amylopectin from the transgenic plants accumulated more relatively short chains than that from control plants and the sizes of starch granules were reduced. The starch granules from the transgenic plants contained a greater amount of granule-bound starch synthase enzyme, which led to an increase in the maximum activity of the enzyme per unit starch tested. The K(m) for ADP-glucose was, at most, only slightly altered in the transgenic lines. Potato plants containing reduced AGPase activity were also transformed with a bacterial gene coding for AGPase to test whether this enzyme can incorporate phosphate monoesters into amylopectin. A slight increase in phosphate contents in the starch in comparison with the untransformed control was found, but not in comparison with starch from the line with reduced AGPase activity into which the bacterial gene was transformed.Key words: ADP-glucose pyrophosphorylase. Amylopectin structure. Amylose. Solanum (starch. tuber). Starch granule size. Starch phosphorylation

Journal Article↗
PubMed1999

Cloning and functional analysis of a cDNA encoding a starch synthase from potato (Solanum tuberosum L.) that is predominantly expressed in leaf tissue.

Three isoforms of starch synthase (SS) were shown to be present in soluble potato tuber extracts by activity staining after native gel electrophoresis. A cDNA encoding SSI from rice was used as a probe to clone a corresponding cDNA from potato. The deduced amino acid sequence identified the protein as an SS from potato with an M(r) of 70.6 kDa for the immature enzyme including its transit peptide. This novel isoform was designated SSI. An analysis of the expression pattern of the gene indicated that SSI is predominantly expressed in sink and source leaves, and, to a lower extent in tubers. In several independent transgenic potato lines, where the expression of SSI was repressed using the antisense approach, the activity of a specific SS isoform was reduced to non-detectable levels as determined through activity staining after native gel electrophoresis. The reduction in the amount of this isoform of SS did not lead to any detectable changes in starch structure, probably due to the fact that this isoform only represents a minor activity in potato tubers.

Amino Acid Sequence↗
PubMed1996

Cloning and functional analysis of a cDNA encoding a novel 139 kDa starch synthase from potato (Solanum tuberosum L.).

Three isoforms of starch synthase were shown to be present in soluble potato tuber extracts by activity staining after native gel electrophoresis. An antibody directed against a domain conserved in starch synthases was used to clone a cDNA for one of these isoforms by screening a tuber-specific expression library. A partial cDNA of 2.6 kbp was obtained and used to isolate a full-length cDNA of 4167 bp. The deduced amino acid sequence identifies the protein as a novel type of starch synthase from potato with a molecular mass of 139.2 kDa for the immature enzyme including its transit peptide. This novel isoform was designated SS III. An analysis of the expression pattern of the gene indicates that SS III is equally expressed in tubers of different developmental stages as well as in sink and source leaves. In several independent transgenic potato lines, where the expression of SS III was repressed using the antisense approach, the activity of a specific starch synthase isoform was reduced to non-detectable levels as determined through activity staining after native gel electrophoresis. The reduction of this isoform of starch synthase leads to the synthesis of a structurally modified starch in the transgenic plants: there is a drastic change in granule morphology and an increased level of covalently linked phosphate.

Amino Acid Sequence↗
PubMed1984

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