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@ARTICLE{vanDongen:28893,
      author       = {van Dongen, J. T. and Schurr, U. and Pfister, M. and
                      Geigenberger, P.},
      title        = {{P}hloem metabolism and function have to cope with low
                      internal oxygen},
      journal      = {Plant physiology},
      volume       = {131},
      issn         = {0032-0889},
      address      = {Rockville, Md.: Soc.},
      publisher    = {JSTOR},
      reportid     = {PreJuSER-28893},
      pages        = {1529 - 1543},
      year         = {2003},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {We have investigated the consequences of endogenous
                      limitations in oxygen delivery for phloem transport in
                      Ricinus communis. In situ oxygen profiles were measured
                      directly across stems of plants growing in air $(21\%$ [v/v]
                      oxygen), using a microsensor with a tip diameter of
                      approximately 30 microm. Oxygen levels decreased from $21\%$
                      (v/v) at the surface to $7\%$ (v/v) in the vascular region
                      and increased again to $15\%$ (v/v) toward the hollow center
                      of the stem. Phloem sap exuding from small incisions in the
                      bark of the stem was hypoxic, and the ATP to ADP ratio (4.1)
                      and energy charge (0.78) were also low. When 5-cm stem
                      segments of intact plants were exposed to zero external
                      oxygen for 90 min, oxygen levels within the phloem decreased
                      to approximately $2\%$ (v/v), and ATP to ADP ratio and
                      adenylate energy charge dropped further to 1.92 and 0.68,
                      respectively. This was accompanied by a marked decrease in
                      the phloem sucrose (Suc) concentration and Suc transport
                      rate, which is likely to be explained by the inhibition of
                      retrieval processes in the phloem. Germinating seedlings
                      were used to analyze the effect of a stepwise decrease in
                      oxygen tension on phloem transport and energy metabolism in
                      more detail. Within the endosperm embedding the
                      cotyledons-next to the phloem loading sites-oxygen decreased
                      from approximately $14\%$ (v/v) in 6-d-old seedlings down to
                      approximately $6\%$ (v/v) in 10-d-old seedlings. This was
                      paralleled by a similar decrease of oxygen inside the
                      hypocotyl. When the endosperm was removed and cotyledons
                      incubated in a 100 mM Suc solution with $21\%,$ $6\%,$
                      $3\%,$ or $0.5\%$ (v/v) oxygen for 3 h before phloem sap was
                      analyzed, decreasing oxygen tensions led to a progressive
                      decrease in phloem energy state, indicating a partial
                      inhibition of respiration. The estimated ratio of NADH to
                      NAD(+) in the phloem exudate remained low (approximately
                      0.0014) when oxygen was decreased to $6\%$ and $3\%$ (v/v)
                      but increased markedly (to approximately 0.008) at $0.5\%$
                      (v/v) oxygen, paralleled by an increase in lactate and
                      ethanol. Suc concentration and translocation decreased when
                      oxygen was decreased to $3\%$ and $0.5\%$ (v/v). Falling
                      oxygen led to a progressive increase in amino acids,
                      especially of alanine, gamma-aminobutyrat, methionine, and
                      isoleucine, a progressive decrease in the C to N ratio, and
                      an increase in the succinate to malate ratio in the phloem.
                      These results show that oxygen concentration is low inside
                      the transport phloem in planta and that this results in
                      adaptive changes in phloem metabolism and function.},
      keywords     = {Adaptation, Physiological / Adenosine Triphosphate:
                      metabolism / Amino Acids: metabolism / Biological Transport,
                      Active: physiology / Energy Metabolism / Fermentation /
                      Glycolysis / Malates: metabolism / NAD: metabolism / Oxygen:
                      metabolism / Phosphorus: metabolism / Plant Structures:
                      cytology / Plant Structures: metabolism / Ricinus: growth
                      $\&$ development / Ricinus: metabolism / Seedling: growth
                      $\&$ development / Seedling: metabolism / Succinic Acid:
                      metabolism / Sucrose: metabolism / Amino Acids (NLM
                      Chemicals) / Malates (NLM Chemicals) / Succinic Acid (NLM
                      Chemicals) / NAD (NLM Chemicals) / Adenosine Triphosphate
                      (NLM Chemicals) / Sucrose (NLM Chemicals) / malic acid (NLM
                      Chemicals) / Phosphorus (NLM Chemicals) / Oxygen (NLM
                      Chemicals) / J (WoSType)},
      cin          = {ICG-III},
      ddc          = {580},
      cid          = {I:(DE-Juel1)VDB49},
      pnm          = {Chemie und Dynamik der Geo-Biosphäre},
      pid          = {G:(DE-Juel1)FUEK257},
      shelfmark    = {Plant Sciences},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:12692313},
      pmc          = {pmc:PMC166912},
      UT           = {WOS:000185076400004},
      doi          = {10.1104/pp.102.017202},
      url          = {https://juser.fz-juelich.de/record/28893},
}