Amino Acid Metabolism in Higher Plants

Amino acid metabolism in higher plants encompasses a finely tuned network of biosynthetic and catabolic routes that underlie protein assembly, stress resilience and intercellular signalling. Biosynthesis of the twenty canonical amino acids occurs predominantly in plastids and mitochondria via distinct metabolic families: the glutamate family provides glutamine, proline and arginine; the aspartate family yields lysine, threonine, methionine and isoleucine; the aromatic family synthesises phenylalanine, tyrosine and tryptophan through the shikimate pathway; and the branched-chain family generates valine, leucine and isoleucine. Each pathway is subject to feedback inhibition by end-products, ensuring homeostasis of nitrogen and carbon resources. Catabolic processes recycle amino acids to supply energy and carbon skeletons under stress or senescence, often involving compartmentalisation between mitochondria, peroxisomes and the cytosol. Non-proteinogenic amino acids, such as β-alanine and γ-aminobutyric acid, extend metabolic versatility by functioning in osmoprotection, defence and hormone biosynthesis. Integration with central carbon metabolism and electron transport chains permits dynamic adaptation to environmental fluctuations. Insights into the regulation of key enzymes, transporter proteins and transcriptional networks have illuminated opportunities for crop improvement, enabling enhanced nutritional quality, abiotic stress tolerance and sustainable nitrogen use.

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Amino Acid Metabolism in Higher Plants publication trend

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Technical terms

Amino acid metabolism: The network of enzymatic pathways by which amino acids are synthesised, interconverted and degraded in plants.

Non-proteinogenic amino acid: An amino acid not incorporated into proteins but serving specialised roles in defence, signalling or stress tolerance.

Feedback inhibition: Regulatory mechanism where an end-product binds to an upstream enzyme, reducing its activity to maintain metabolic balance.

Electron-transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO): A mitochondrial complex that transfers electrons from dehydrogenases to the ubiquinone pool, supporting respiration.

Compartmentation: Spatial separation of metabolic pathways into organelles such as chloroplasts, mitochondria and peroxisomes to optimise flux and regulation.

References

1. Identification of the 2-Hydroxyglutarate and Isovaleryl-CoA Dehydrogenases as Alternative Electron Donors Linking Lysine Catabolism to the Electron Transport Chain of Arabidopsis Mitochondria. The Plant Cell (2010).
2. The Synthesis and Role of β-Alanine in Plants. Frontiers in Plant Science (2019).
3. Peroxisomal Metabolism of Propionic Acid and Isobutyric Acid in Plants*. Journal of Biological Chemistry (2007).
4. Reductive Degradation of Pyrimidines V. ENZYMATIC CONVERSION OF N-CARBAMYL-β-ALANINE TO β-ALANINE, CARBON DIOXIDE, AND AMMONIA. Journal of Biological Chemistry (1960).
5. Solanum lycopersicum Seedlings. Metabolic Responses Induced by the Alkamide Affinin. Metabolites (2021).