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. 2023 Sep 28;12(19):3410. doi: 10.3390/plants12193410

Figure 1.

Figure 1

Metabolism of amino acids under stress conditions. (A), catabolic reactions involving BCAA or lysine producing electrons, supplied to oxidative phosphorylation in mitochondria and acetylCoA for tricarboxylic acid cycle (TCA). Catabolism of lysine provides aminoadipate and N-hydroxy-pipecolic acid, signal molecules for SAR. Reductases involved in dehydropipecolic acids reduction are not completely identified; SARD4 has been discovered but it is not the unique enzyme catalyzing this conversion. ALD1, aminotransferase; ALDH, aldehyde dehydrogenase; BCAAT, BCAA transaminase; BCKDH, branched chain α-keto acid dehydrogenase; ETF, electron transfer flavoprotein; ETF-QO, electron transfer flavoprotein:ubiquinone oxidase; FMO1, flavin monoxygenase 1; IVDH, isovalerylCoA dehydrogenase; LKR, lysine-ketoglutarate reductase; SDH, saccharopine dehydrogenase. (B), proline cycling between synthesis and turnover. In leaves protein is synthetized, especially consuming reducing power from photosynthesis. Proline is putatively transferred in roots, where its catabolism provides electrons to fuel the mitochondria electron chain and then root growth. ProDH, proline dehydrogenase; P5CDH, pyrroline-5-carboxylate dehydrogenase; P5CR, pyrroline-5-carboxylate reductase; P5CS, pyrroline-5-carboxylate synthase. Enzyme localization is shown as background color and explained in the legend.