@article{MalinovaSteupFettke2011,
  author    = {Malinova, Irina and Steup, Martin and Fettke, J{\"o}rg},
  title     = {Starch-related cytosolic heteroglycans in roots from Arabidopsis thaliana},
  series = {Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants},
  volume    = {168},
  journal   = {Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants},
  number    = {12},
  publisher = {Elsevier},
  address   = {Jena},
  issn      = {0176-1617},
  doi       = {10.1016/j.jplph.2010.12.008},
  pages     = {1406 -- 1414},
  year      = {2011},
  abstract  = {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.},
  language  = {en}
}
@article{MalinovaSteupFettke2013,
  author    = {Malinova, Irina and Steup, Martin and Fettke, J{\"o}rg},
  title     = {Carbon transitions from either Calvin cycle or transitory starch to heteroglycans as revealed by 14-C-labeling experiments using protoplasts from Arabidopsis},
  series = {Physiologia plantarum},
  volume    = {149},
  journal   = {Physiologia plantarum},
  number    = {1},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0031-9317},
  doi       = {10.1111/ppl.12033},
  pages     = {25 -- 44},
  year      = {2013},
  abstract  = {Plants metabolize transitory starch by precisely coordinated plastidial and cytosolic processes. The latter appear to include the action of water-soluble heteroglycans (SHG(in)) whose monosaccharide pattern is similar to that of apoplastic glycans (SHG(ex)) but, unlike SHG(ex), SHG(in) strongly interacts with glucosyl transferases. In this study, we analyzed starch metabolism using mesophyll protoplasts from wild-type plants and two knock-out mutants [deficient in the cytosolic transglucosidase, disproportionating isoenzyme 2 (DPE2) or the plastidial phosphoglucomutase (PGM1)] from Arabidopsis thaliana. Protoplasts prelabeled by photosynthetic (CO2)-C-14 fixation were transferred to an unlabeled medium and were darkened or illuminated. Carbon transitions from the Calvin cycle or from starch to both SHG(in) and SHG(ex) were analyzed. In illuminated protoplasts, starch turn-over was undetectable but darkened protoplasts continuously degraded starch. During illumination, neither the total C-14 content nor the labeling patterns of the sugar residues of SHG(in) were significantly altered but both the total amount and the labeling of the constituents of SHG(ex) increased with time. In darkened protoplasts, the C-14-content of most of the sugar residues of SHG(in) transiently and strongly increased and then declined. This effect was not observed in any SHG(ex) constituent. In darkened DPE2-deficient protoplasts, none of the SHG(in) constituents exhibited an essential transient increase in labeling. In contrast, some residues of SHG(in) from the PGM1 mutant exhibited a transient increase in label but this effect significantly differed from that of the wild type. Two conclusions are reached: first, SHG(in) and SHG(ex) exert different metabolic functions and second, SHG(in) is directly involved in starch degradation.},
  language  = {en}
}
@phdthesis{Malinova2012,
  author    = {Malinova, Irina},
  title     = {Analysis of starch metabolism in connection with altered enzyme activities related to central carbon turn-over in Arabidopsis thaliana},
  address   = {Potsdam},
  pages     = {223 S.},
  year      = {2012},
  language  = {en}
}
@article{FettkeMalinovaEckermannetal.2009,
  author    = {Fettke, J{\"o}rg and Malinova, Irina and Eckermann, Nora and Steup, Martin},
  title     = {Cytosolic heteroglycans in photoautotrophic and in heterotrophic plant cells},
  issn      = {0031-9422},
  doi       = {10.1016/j.phytochem.2009.03.016},
  year      = {2009},
  abstract  = {In plants several 'starch-related' enzymes exist as plastid- and cytosol-specific isoforms and in some cases the extraplastidial isoforms represent the majority of the enzyme activity. Due to the compartmentation of the plant cells, these extraplastidial isozymes have no access to the plastidial starch granules and, therefore, their in vivo function remained enigmatic. Recently, cytosolic heteroglycans have been identified that possess a complex pattern of the monomer composition and glycosidic bonds. The glycans act both as acceptors and donors for cytosolic glucosyl transferases. In autotrophic tissues the heteroglycans are essential for the nocturnal starch-sucrose conversion. In this review we summarize the current knowledge of these glycans, their interaction with glucosyl transferases and their possible cellular functions. We include data on the heteroglycans in heterotrophic plant tissues and discuss their role in intracellular carbon fluxes that originate from externally supplied carbohydrates.},
  language  = {en}
}