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- Solymosi, K., et al.
(author)
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Plastid differentiation and chlorophyll biosynthesis in different leaf layers of white cabbage (Brassica oleracea cv. capitata)
- 2004
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In: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 121:3, s. 520-529
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Journal article (peer-reviewed)abstract
- The contents of protochlorophyllide, protochlorophyll and chlorophyll together with the native arrangements of the pigments and the plastid ultrastructure were studied in different leaf layers of white cabbage (Brassica oleracea cv. capitata) using absorption, 77 K fluorescence spectroscopy and transmission electron microscopy. The developmental stage of the leaves was determined using the differentiation of the stoma complexes as seen by scanning electron microscopy and light microscopy. The pigment content showed a gradual decrease from the outer leaf layer towards the central leaves. The innermost leaves were in a primordial stage in many aspects; they were large but had typical proplastids with few simple inner membranes, and contained protochlorophyllide and its esters in a 2 : 1 ratio and no chlorophyll. Short-wavelength, not flash-photoactive protochlorophyllide and/or protochlorophyll forms emitting at 629 and 636 nm were dominant in the innermost leaves. These leaves also had small amounts of the 644 and 654 nm emitting, flash-photoactive protochlorophyllide forms. Rarely prolamellar bodies were observed in this layer. The outermost leaves had the usual characteristics of fully developed green leaves. The intermediary layers contained chlorophyll a and chlorophyll b besides the protochlorophyll(ide) pigments and had various intermediary developmental stages. Spectroscopically two types of intermediary leaves could be distinguished: one with only a 680 nm emitting chlorophyll a form and a second with bands at 685, 695 and 730 nm, corresponding to chlorophyll-protein complexes of green leaves. In these leaves, a large variety of chloroplasts were found. The data of this work show that etioplasts, etio-chloroplasts or chloro-etioplasts as well as etiolated leaves do exist in the nature and not only under laboratory conditions. The specificity of cabbage leaves compared with those of dark-grown seedlings is the retained primordial or intermediary developmental stage of leaves in the inner layers for very long (even for a few month) period. This opens new developmental routes leading to formation of specially developed plastids in the various cabbage leaf layers. The study of these plastids provided new information for a better understanding of the plastid differentiation and the greening process.
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- Stasiewicz, Kristof, et al.
(author)
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Modelling of mirror mode structures as propagating slow magnetosonic solitons
- 2009
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In: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:12, s. 4379-4389
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Journal article (peer-reviewed)abstract
- Cluster measurements in the magnetosheath with spacecraft separations of 2000 km indicate that magnetic pulsations interpreted as mirror mode structures are not frozen in plasma flow, but do propagate with speeds of up to similar to 50 km/s. Properties of these pulsations are shown to be consistent with propagating slow magnetosonic solitons. By using nonlinear two fluid theory we demonstrate that the well known classical mirror instability condition corresponds to a small subset in a continuum of exponentially varying solutions. With the measured plasma moments we have determined parameters of the polybaric pressure model in the region of occurrence of mirror type structures and applied it to numerical modelling of these structures. In individual cases we obtain excellent agreement between observed mirror mode structures and numerical solutions for magnetosonic solitons.
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- Strumik, M., et al.
(author)
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Evolution of large-scale magnetosonic structures to trains of solitary waves
- 2011
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In: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116, s. A07209-
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Journal article (peer-reviewed)abstract
- Large-amplitude magnetic pulsations on ion inertial length scales are often observed in space plasmas, but their theoretical explanation is still controversial. We discuss a possible mechanism, different from ideas based on the classical plasma instabilities, for the generation of these pulsations. It is demonstrated that a competition between dispersion and wave steepening processes can lead to the transformation of a large-scale magnetosonic structure into trains of solitons. This kind of longitudinal filamentation is possible for both slow and fast magnetosonic perturbations. Results of numerical simulations are compared with Cluster spacecraft measurements and show that the steepening filamentation mechanism can explain the emergence of a certain class of solitary waves observed in space plasmas.
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