Skip Navigation



AOBPreview published online on August 26, 2005
Annals of Botany, doi:10.1093/aob/mci254
This Article
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
96/6/1019    most recent
mci254v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by YANG, Z.
Right arrow Articles by MIDMORE, D. J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by YANG, Z.
Right arrow Articles by MIDMORE, D. J.
Agricola
Right arrow Articles by YANG, Z.
Right arrow Articles by MIDMORE, D. J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oupjournals.org
Received March 24, 2005
Revised June 14, 2005
Accepted July 18, 2005

Article

A Model for the Circadian Oscillations in Expression and Activity of Nitrate Reductase in Higher Plants

ZONGJIAN YANG 1* and DAVID J. MIDMORE 1

1 Plant Sciences Group, School of Biological and Environmental Sciences, Central Queensland University, Rockhampton, Qld 4702, Australia

* To whom correspondence should be addressed.
ZONGJIAN YANG, E-mail: z.yang{at}cqu.edu.au


  Abstract

• Background and Aims Nitrate is the major nitrogen source for many plants. The first step of the nitrate assimilation pathway is the reduction of nitrate to nitrite, catalysed by nitrate reductase (NR). Circadian oscillations in expression and activity of NR have been demonstrated in many plant species. The pathway by which this circadian behaviour is regulated remains to be elucidated. In this study, based on recent experimental observations, a mathematical model is proposed to explain the origin of diurnal and circadian oscillations in NR gene expression and enzyme activity.

• Methods The dynamic model is based on the feedback interconnections between NR and its substrate, nitrate. In the model, NR activity is regulated at the transcriptional level, in response to the balance between nitrate influx and reduction, and at the post-translational levels in response to signals from carbon assimilation. Conditions for the model system to generate self-sustained circadian oscillations are investigated by numerical simulations.

• Key Results and Conclusions Under light/dark cycles, the simulation results are in agreement with the observed diurnal pattern of changes in leaf nitrate concentration, NR transcript level and NR activity. Within a range of kinetic parameter values, circadian oscillation behaviour persists even under constant light, with periods of approx. 24 h. These simulation results suggest that sustained circadian oscillations can originate from the feedback interactions between NR and its substrate, nitrate, without the need to postulate the existence of an endogenous ‘circadian clock’.

Keywords: Nitrate reductase, model, nitrate reduction, circadian rhythms, diurnal oscillations, nitrogen metabolism.
Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?




Disclaimer: Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.