Nitrate as a Signal in Arabidopsis

Abstract

This thesis describes an investigation of nitrate signalling in Arabidopsis thaliana leaf cells. The expression and activity of nitrate transporters and assimilatory enzymes are under complex regulation by mechanisms that are not yet fully understood. Experiments were designed to investigate the relationships between cytosolic ion activity changes and the regulation of nitrate transporters and assimilatory enzymes.

Two different approaches were used. Firstly, cytosolic ion activity changes were measured under light-dark transitions, treatment known to affect the regulation of nitrate transporters and assimilatory enzymes. These changes were initially studied using ion-selective microelectrodes. Light-dark transitions were shown to cause changes in cytosolic nitrate activity in mesophyll cells. Dark treatment caused an increase in cytosolic nitrate activity, light treatment a decrease. Plants without functional nitrate reductase (NR) did not show such changes and a higher constant level of cytosolic nitrate activity was observed compared with wild type, suggesting that NR activity has a role in cytosolic nitrate activity changes. These results are consistent with a signalling role for cytosolic nitrate activity in the regulation of nitrate transporters and assimilatory enzymes. The role of NR in influencing cytosolic pH was investigated using pH-selective microelectrodes. The microelectrode measurements were extremely difficult and time consuming so as an alternative pH-indicator dyes were tested but were not distributed in the cytosol of mesophyll cells.

The second approach involved the use of nitrate-inducible luciferase reporter plants. A photomultiplier tube/fibre optic cable system was developed and used to quantify luminescence from these plants. A low-light imaging camera was also used. Both systems showed that the reporter plants provided were unsuitable for the study of nitrate-induction. Alternative nitrate-inducible reporter plants were produced, which were shown to be nitrate-inducible and suitable for nitrate-induction studies.

The results presented provide supporting evidence for the hypothesis that NR-dependent changes in cytosolic nitrate activity may function as signals in Arabidopsis mesophyll cells.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata