Endogenous ascorbate concentrations remained unaffected following exposure of excised radish hypocotyls to various forms of stress that included aerobic, anaerobic, light, dark, 254 and 366 nm ultraviolet and contact with 33 mM sodium nitroprusside. Exposure of intact radish plants to a high-oxygen atmosphere produced significant drops in the ascorbate concentrations of the hypocotyl tissue. Irrigation of the roots of radish plants with 50 mM sodium ascorbate did not affect hypocotyl acorbate concentrations- Exposing radish plants to (50 mM) sodium ascorbate by watering through laterally trimmed roots and vacuum infiltration failed to increase endogenous ascorbate concentrations. Excised radish leaves fed 0.1 M L-galactonolactone showed a clear increase in L-gascorbate concentrations. Hypocotyls bathed in 0.1 M L-galactonolactone showed no increase in L-ascorbate concentrations. Radish plants fed L-galactonolactone through an incision in a leaf petiole showed a clear increase in L-ascorbate concentrations in the fed leaf as well as neighbouring leaves; however, no increase in ascorbate concentrations was seen in the hypocotyl. Hypocotyl disks bathed in de-gassed water for 24 hours showed production of L-aseorbate after being fed L-galactonolactone as well as clear uptake of L-[6<sup>3</sup>H]galactonolactone with a K<sub>m</sub> of 0.24 nM. A hypocotyl disk fed 17 MBq of L-[6-<sup>3</sup>H]galactonolactone produced cellular radiolabelled ascorbate as well as several other unknown metabolic products ‘The hypocotyl bathing solution contained several unknown products released by the cells into the extracellulax fluid. Compounds were detected by electrophoretic fluoragraphy at pH 6.5 and by chromatographic fluorography BuOH:HOAc:H<sub>2</sub>O (12:3:5). Unknown compounds were detected by this method while tartrate, threonate and oxalate, metabolites of ascorbate metabolism were not detected.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641215 |
| Date | January 2005 |
| Creators | Bain, Malcolm S. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10702 |
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