TY - JOUR A1 - Malinova, Irina A1 - Steup, Martin A1 - Fettke, Jörg T1 - Starch-related cytosolic heteroglycans in roots from Arabidopsis thaliana JF - Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants N2 - Both photoautotrophic and heterotrophic plant cells are capable of accumulating starch inside the plastid. However, depending on the metabolic state of the respective cell the starch-related carbon fluxes are different. The vast majority of the transitory starch biosynthesis relies on the hexose phosphate pools derived from the reductive pentose phosphate cycle and, therefore, is restricted to ongoing photosynthesis. Transitory starch is usually degraded in the subsequent dark period and mainly results in the formation of neutral sugars, such as glucose and maltose, that both are exported into the cytosol. The cytosolic metabolism of the two carbohydrates includes reversible glucosyl transfer reactions to a heteroglycan that are mediated by two glucosyl transferases. DPE2 and PHS2 (or, in all other species, Pho2). In heterotrophic cells, accumulation of starch mostly depends on the long distance transport of reduced carbon compounds from source to sink organs and, therefore, includes as an essential step the import of carbohydrates from the cytosol into the starch forming plastids. In this communication, we focus on starch metabolism in heterotrophic tissues from Arabidopsis thaliana wild type plants (and in various starch-related mutants as well). By using hydroponically grown A. thaliana plants, we were able to analyse starch-related biochemical processes in leaves and roots from the same plants. Within the roots we determined starch levels and the morphology of native starch granules. Cytosolic and apoplastic heteroglycans were analysed in roots and compared with those from leaves of the same plants. A. thaliana mutants lacking functional enzymes either inside the plastid (such as phosphoglucomutase) or in the cytosol (disproportionating isoenzyme 2 or the phosphorylase isozyme, PHS2) were included in this study. In roots and leaves from the three mutants (and from the respective wild type organ as well), starch and heteroglycans as well as enzyme patterns were analysed. KW - Cytosolic heteroglycans KW - Cytosolic glucosyl transferases KW - Photoautotrophic tissues KW - Heterotrophic tissues KW - Starch metabolism Y1 - 2011 U6 - https://doi.org/10.1016/j.jplph.2010.12.008 SN - 0176-1617 VL - 168 IS - 12 SP - 1406 EP - 1414 PB - Elsevier CY - Jena ER - TY - JOUR A1 - Orawetz, Tom A1 - Malinova, Irina A1 - Orzechowski, Slawomir A1 - Fettke, Jörg T1 - Reduction of the plastidial phosphorylase in potato (Solanum tuberosum L.) reveals impact on storage starch structure during growth at low temperature JF - Plant physiology and biochemistry : an official journal of the Federation of European Societies of Plant Physiology N2 - Tubers of potato (Solanum tuberosum L.), one of the most important crops, are a prominent example for an efficient production of storage starch. Nevertheless, the synthesis of this storage starch is not completely understood. The plastidial phosphorylase (Phol; EC 2.4.11) catalyzes the reversible transfer of glucosyl residues from glucose-1-phosphate to the non-reducing end of alpha-glucans with the release of orthophosphate. Thus, the enzyme is in principle able to act during starch synthesis. However, so far under normal growth conditions no alterations in tuber starch metabolism were observed. Based on analyses of other species and also from in vitro experiments with potato tuber slices it was supposed, that Phol has a stronger impact on starch metabolism, when plants grow under low temperature conditions. Therefore, we analyzed the starch content, granule size, as well as the internal structure of starch granules isolated from potato plants grown under low temperatures. Besides wild type, transgenic potato plants with a strong reduction in the Phol activity were analyzed. No significant alterations in starch content and granule size were detected. In contrast, when plants were cultivated at low temperatures the chain length distributions of the starch granules were altered. Thus, the granules contained more short glucan chains. That was not observed in the transgenic plants, revealing that Pho1 in wild type is involved in the formation of the short glucan chains, at least at low temperatures. (C) 2016 Elsevier Masson SAS. All rights reserved. KW - Potato KW - Solanum tuberosum L. KW - Plastidial phosphorylase KW - Starch synthase KW - Starch metabolism KW - Starch granule Y1 - 2016 U6 - https://doi.org/10.1016/j.plaphy.2016.01.013 SN - 0981-9428 VL - 100 SP - 141 EP - 149 PB - Elsevier CY - Paris ER -