Plants tightly regulate the GS-GOGAT cycle. This control ensures efficient nitrogen assimilation. Moreover, it maintains carbon-nitrogen balance in cells.
First, transcriptional regulation plays a major role. Plants induce GS and GOGAT genes in response to nitrogen status. Ammonium supply triggers expression of specific isoforms. For example, GLN1;2 and GLT1 rise in Arabidopsis roots.
However, ammonium does not directly induce these genes. Instead, glutamine or its downstream metabolites signal the response. Experiments with GS inhibitors like MSX confirm this pathway. When GS blocks, ammonium fails to upregulate GOGAT.
Additionally, light strongly influences regulation. Chloroplastic GS2 and Fd-GOGAT activate in illuminated leaves. They handle photorespiratory ammonium efficiently. Cytosolic GS1 responds more to developmental and stress cues.
Plant growth regulators also modulate expression. Cytokinins and auxins differentially affect GS-GOGAT genes. In shoots versus roots, responses vary markedly.
Furthermore, post-translational mechanisms fine-tune activity. Phosphorylation modifies GS isoforms. 14-3-3 proteins bind and regulate GS stability. Redox changes and nitric oxide influence enzyme function too.
Allosteric control adds another layer. Glutamate acts as both substrate and regulator. In some cases, GS shows negatively cooperative behavior.
Environmental factors impact regulation. Nitrogen deficiency derepresses GS and GOGAT. Excess ammonium or glutamine feedback inhibits excess activity.
Scientists target these controls for crop improvement. Overexpression of key isoforms boosts nitrogen use efficiency. Consequently, yields rise in cereals under limited nitrogen.
Overall, multi-level regulation keeps GS-GOGAT responsive. Plants adapt nitrogen metabolism dynamically. This flexibility supports growth and survival. Understanding these mechanisms unlocks better agriculture.
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