GABA-regulated transamination generates alternative carbon skeleton for root nitrogen assimilation of wheat under waterlogging stress

Abstract

Understanding the mutual regulation of carbon and nitrogen metabolism under waterlogging can provide a theoretical basis for nutrient management under such stress. We conducted pot experiments using two wheat (Triticum aestivum) cultivars, AK58 (waterlogging-sensitive) and XM25 (waterlogging-tolerant), under 7 days of waterlogging and control conditions. Waterlogging treatment decreased shoot nitrogen content, dry matter, and yield compared with the control, and the extent of these reductions was lower in XM25 than in AK58. Under waterlogged conditions, root glutamine synthetase (GS) and glutamate synthase (GOGAT) activities decreased under waterlogging treatment due to insufficient supply of α-ketoglutaric acid, and the decrease of root nitrogen assimilation was lower in XM25 than in AK58. In contrast, glutamic-pyruvic transaminase (GPT) activity increased, and alanine (Ala) and γ-aminobutyric acid (GABA) content increased significantly under waterlogging conditions, especially in XM25. To verify the effect of GABA, we applied exogenous GABA treatment and found that exogenous GABA upregulated pyruvate kinase (PK) and GPT activity, resulting in higher ¹⁵N-Ala and α-ketoglutaric acid content. Correspondingly, GABA treatment promoted GS and GOGAT activity in roots and increased shoot nitrogen content, indicating that GABA upregulated the glutamic-pyruvic transamination to supplement carbon skeletons for root nitrogen assimilation. In conclusion, enhancing the carbon skeleton anaplerotic pathway through transamination promoted nitrogen assimilation in roots under waterlogging conditions, and GABA acts as a regulator in this pathway.