Molecular crosstalk and the regulation of C- and N- responsive genes
Changes in gene expression can contribute to adjustment in the balance of C/N assimilation and storage balance in plants on a time scale that lies between that of rapid, fine tuning of metabolism, and long-term changes in morphology and development. Gene expression also integrates signals from these other levels of control (Koch, 1996). For short-term adjustments, it can be effectively argued that even rapid changes in gene expression, such as for NR (Crawford, 1995; Foyer et al., 1993; Vincentz et al., 1993), are likely to have less regulatory influence than direct effectors of fine control via allosteric modulation or enzyme phosphorylation (Foyer et al., 1993; Oaks, 1994; Quick and Schaffer, 1996). However, the ultimate amplitude of change over an extended period is greater at the level of gene expression, and thus provides a means of coarse control for extending the outside limits of more fine-tuned mechanisms for metabolic balance. In general, responses at the level of gene expression also reflect similar changes in enzyme regulation, and further amplify effects of these over time. Resulting influence on still longer-term changes in plant form can, in turn, favour acquisition versus utilization of C and N resources.