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000028893 0247_ $$2DOI$$a10.1104/pp.102.017202
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000028893 084__ $$2WoS$$aPlant Sciences
000028893 1001_ $$0P:(DE-HGF)0$$avan Dongen, J. T.$$b0
000028893 245__ $$aPhloem metabolism and function have to cope with low internal oxygen
000028893 260__ $$aRockville, Md.: Soc.$$bJSTOR$$c2003
000028893 300__ $$a1529 - 1543
000028893 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article
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000028893 440_0 $$04987$$aPlant Physiology$$v131$$x0032-0889
000028893 500__ $$aRecord converted from VDB: 12.11.2012
000028893 520__ $$aWe 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.
000028893 536__ $$0G:(DE-Juel1)FUEK257$$2G:(DE-HGF)$$aChemie und Dynamik der Geo-Biosphäre$$cU01$$x0
000028893 588__ $$aDataset connected to Web of Science, Pubmed
000028893 650_2 $$2MeSH$$aAdaptation, Physiological
000028893 650_2 $$2MeSH$$aAdenosine Triphosphate: metabolism
000028893 650_2 $$2MeSH$$aAmino Acids: metabolism
000028893 650_2 $$2MeSH$$aBiological Transport, Active: physiology
000028893 650_2 $$2MeSH$$aEnergy Metabolism
000028893 650_2 $$2MeSH$$aFermentation
000028893 650_2 $$2MeSH$$aGlycolysis
000028893 650_2 $$2MeSH$$aMalates: metabolism
000028893 650_2 $$2MeSH$$aNAD: metabolism
000028893 650_2 $$2MeSH$$aOxygen: metabolism
000028893 650_2 $$2MeSH$$aPhosphorus: metabolism
000028893 650_2 $$2MeSH$$aPlant Structures: cytology
000028893 650_2 $$2MeSH$$aPlant Structures: metabolism
000028893 650_2 $$2MeSH$$aRicinus: growth & development
000028893 650_2 $$2MeSH$$aRicinus: metabolism
000028893 650_2 $$2MeSH$$aSeedling: growth & development
000028893 650_2 $$2MeSH$$aSeedling: metabolism
000028893 650_2 $$2MeSH$$aSuccinic Acid: metabolism
000028893 650_2 $$2MeSH$$aSucrose: metabolism
000028893 650_7 $$00$$2NLM Chemicals$$aAmino Acids
000028893 650_7 $$00$$2NLM Chemicals$$aMalates
000028893 650_7 $$0110-15-6$$2NLM Chemicals$$aSuccinic Acid
000028893 650_7 $$053-84-9$$2NLM Chemicals$$aNAD
000028893 650_7 $$056-65-5$$2NLM Chemicals$$aAdenosine Triphosphate
000028893 650_7 $$057-50-1$$2NLM Chemicals$$aSucrose
000028893 650_7 $$06915-15-7$$2NLM Chemicals$$amalic acid
000028893 650_7 $$07723-14-0$$2NLM Chemicals$$aPhosphorus
000028893 650_7 $$07782-44-7$$2NLM Chemicals$$aOxygen
000028893 650_7 $$2WoSType$$aJ
000028893 7001_ $$0P:(DE-Juel1)129402$$aSchurr, U.$$b1$$uFZJ
000028893 7001_ $$0P:(DE-HGF)0$$aPfister, M.$$b2
000028893 7001_ $$0P:(DE-HGF)0$$aGeigenberger, P.$$b3
000028893 773__ $$0PERI:(DE-600)2004346-6$$a10.1104/pp.102.017202$$gVol. 131, p. 1529 - 1543$$p1529 - 1543$$q131<1529 - 1543$$tPlant physiology$$v131$$x0032-0889$$y2003
000028893 8567_ $$2Pubmed Central$$uhttp://www.ncbi.nlm.nih.gov/pmc/articles/PMC166912
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