@article{MartinsHejaziFettkeetal.2013,
  author    = {Martins, Marina Camara Mattos and Hejazi, Mahdi and Fettke, J{\"o}rg and Steup, Martin and Feil, Regina and Krause, Ursula and Arrivault, Stephanie and Vosloh, Daniel and Figueroa, Carlos Maria and Ivakov, Alexander and Yadav, Umesh Prasad and Piques, Maria and Metzner, Daniela and Stitt, Mark and Lunn, John Edward},
  title     = {Feedback inhibition of starch degradation in arabidopsis leaves mediated by trehalose 6-phosphate},
  series = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants},
  volume    = {163},
  journal   = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants},
  number    = {3},
  publisher = {American Society of Plant Physiologists},
  address   = {Rockville},
  issn      = {0032-0889},
  doi       = {10.1104/pp.113.226787},
  pages     = {1142 -- 1163},
  year      = {2013},
  abstract  = {Many plants accumulate substantial starch reserves in their leaves during the day and remobilize them at night to provide carbon and energy for maintenance and growth. In this paper, we explore the role of a sugar-signaling metabolite, trehalose-6-phosphate (Tre6P), in regulating the accumulation and turnover of transitory starch in Arabidopsis (Arabidopsis thaliana) leaves. Ethanol-induced overexpression of trehalose-phosphate synthase during the day increased Tre6P levels up to 11-fold. There was a transient increase in the rate of starch accumulation in the middle of the day, but this was not linked to reductive activation of ADP-glucose pyrophosphorylase. A 2- to 3-fold increase in Tre6P during the night led to significant inhibition of starch degradation. Maltose and maltotriose did not accumulate, suggesting that Tre6P affects an early step in the pathway of starch degradation in the chloroplasts. Starch granules isolated from induced plants had a higher orthophosphate content than granules from noninduced control plants, consistent either with disruption of the phosphorylation-dephosphorylation cycle that is essential for efficient starch breakdown or with inhibition of starch hydrolysis by beta-amylase. Nonaqueous fractionation of leaves showed that Tre6P is predominantly located in the cytosol, with estimated in vivo Tre6P concentrations of 4 to 7 mu M in the cytosol, 0.2 to 0.5 mu M in the chloroplasts, and 0.05 mu M in the vacuole. It is proposed that Tre6P is a component in a signaling pathway that mediates the feedback regulation of starch breakdown by sucrose, potentially linking starch turnover to demand for sucrose by growing sink organs at night.},
  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}
}