Journal of Experimental Botany, Vol. 55, No. 401, pp. iv, June 1, 2004
© 2004 Oxford University Press
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This focus section in the Journal of Experimental Botany (JXB) contains three contributions from scientists invited to present papers at the 7th International Symposium on Inorganic Nitrogen Assimilation in Plants, Wageningen, The Netherlands, 23--27 June 2004. The aim of this Symposium series, organized by the European Nitrate and Ammonium Assimilation Group, is to present the current knowledge and ideas on future developments in the field of inorganic nitrogen assimilation in plants. The three papers are focused on the importance of regulatory aspects of nitrogen assimilation at various levels of integration, from the molecular to the whole-plant level. Besides providing an up-to-date insight into the key issues, the three papers also highlight the gaps in the present knowledge, and the prospects for future research.
Lillo et al. review the mechanisms and importance of post-translational regulation of nitrate by phosphorylation, and point out that this form of regulation is important for controlling the formation of toxic products as nitrite and NO. The possible involvement of phosphorylation in the degradation of nitrate reductase in vivo is another key issue addressed in this paper. The regulation of ammonium uptake by plant roots is reviewed by Loque¨ and von Wire¨n. They reveal that various AMT transporters are involved, that differ in biochemical properties, localization and transcriptional regulation. They conclude that ammonium transport is most likely feedback regulated at the cellular level by ammonium efflux, compartmentation, and assimilation. However, a direct regulatory link between these processes and AMT transporters has not yet been established. The regulatory aspects involved in the integration of nitrogen and sulphur metabolism are reviewed by Hesse et al. The paper is focused on the regulation of the biosynthesis of cysteine, the first compound containing both nitrogen and sulphur, and describes the development of molecular tools leading to improved understanding of the biosynthetic mechanisms and regulation of nutrient-induced changes in cysteine formation.
I am grateful to the authors for their contributions, and express my sincere thanks to the JXB for their financial support, and the editing of these papers.
Ineke Stulen
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