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Title: Subcellular compartmentation and remobilization of nitrate in barley
Author: Van der Leij, Martina
ISNI:       0000 0001 3542 2922
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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The work described in this thesis investigated the remobilization of vacuolar stored nitrate in barley, when external nitrate supply was removed after an initial 24 h loading period with 10 mM nitrate. An integrated experimental approach was used which combined whole tissue analysis with measurements made at the cellular level using nitrate selective microelectrodes. Whole tissue analysis for nitrate and measurements of growth rate showed that relative growth rate and shoot: root ratios were maintained for 3-4 days after removal of external nitrate, although root tissue nitrate concentration was decreased to 57 % of initial levels after 24 h and to 29 % after three days without external nitrate supply. Nitrate selective microelectrode measurements recorded in the cytoplasm and vacuole of root epidermal and cortical cells over 24 h after removal of external nitrate showed that cytoplasmic nitrate concentration was maintained over this time at approximately 4-5 mM. Initial vacuolar concentrations were approximately 40 mM for epidermal cells and 68 mM cortical cells. Nitrate was remobilized from the vacuoles of both cell types at the same rate over the 24 h after external nitrate removal (± 1 mM h-1). Measurements of nitrate efflux under these conditions showed that efflux accounted for approximately 4.5 mM nitrate, lost over the first 6 h after removal of external nitrate, after which no detectable nitrate efflux occurred. Measurement of in vitro nitrate reductase activity (NRA) and translocation showed that NRA was maintained in both roots and shoots over 24 h after external nitrate removal, while translocation of nitrate to the shoot was reduced to 28 % of the initial translocation rate measured after 24 h of nitrate supply. The results were combined to develop a model for vacuolar nitrate remobilization in the roots, which suggests that the main function of vacuolar nitrate is to maintain cytosolic nitrate homeostasis and thus the "nitrate induced" state of barley roots during short periods of nitrate deprivation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry