Adenosine stimulates anabolic metabolism in developing castor bean (Ricinus communis L.) cotyledons.
In previous experiments it was shown that Castor-bean (Ricinus communis) endosperm releases carbohydrates, amino acids and nucleoside derivatives, which are subsequently imported into the developing cotyledons (Kombrink and Beevers in Plant Physiol 73:370-376, 1983). To investigate the importance of the most prominent nucleoside adenosine for the metabolism of growing Ricinus seedlings, we supplied adenosine to cotyledons of 5-days-old seedlings after removal of the endosperm. This treatment led to a 16% increase in freshweight of intact seedlings within 16 h, compared to controls. Using detached cotyledons, we followed uptake of radiolabelled adenosine and identified 40% of label in solubles (mostly ATP and ADP), 46% incorporation in RNA and 2.5% in DNA, indicating a highly active salvage pathway. About 7% of freshly imported adenosine entered the phloem, which indicates a major function of adenosine for cotyledon metabolism. Import and conversion of adenosine improved the energy content of cotyledons as revealed by a substantially increased ATP/ADP ratio. This effect was accompanied by slight increases in respiratory activity, decreased levels of hexose phosphates and increased levels of fructose-1,6-bisphosphate and triose phosphates. These alterations indicate a stimulation of glycolytic flux by activation of phosphofructokinase, and accordingly we determined a higher activity of this enzyme. Furthermore the rate of [(14)C]-sucrose driven starch biosynthesis in developing castor-bean is significantly increased by feeding of adenosine. In conclusion, our data indicate that adenosine imported from mobilizing endosperm into developing castor-bean cotyledons fulfils an important function as it promotes anabolic reactions in this rapidly developing tissue.
Flörchinger
Martin
M
Pflanzenphysiologie, Universität Kaiserslautern, Postfach 3049, 67653 Kaiserslautern, Germany.
Zimmermann
Marc
M
Traub
Michaela
M
Neuhaus
H Ekkehard
HE
Möhlmann
Torsten
T
D000241:Adenosine / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D000244:Adenosine Diphosphate / Q000737:chemistry / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000737:chemistry / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002367:Ricinus communis / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D018548:Cotyledon / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D004734:Energy Metabolism; D004789:Enzyme Activation; D005954:Glucosephosphate Dehydrogenase / Q000378:metabolism; D009696:Nucleic Acids / Q000096:biosynthesis; D010100:Oxygen / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development; D013213:Starch / Q000096:biosynthesis*; D014166:Transferases / Q000378:metabolism
D009696:Nucleic Acids; D002245:Carbon Dioxide; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D013213:Starch; D005954:Glucosephosphate Dehydrogenase; D014166:Transferases; D000241:Adenosine; D010100:Oxygen