Fig. 3.

Partitioning of de novo assimilated ¹⁵N towards proline biosynthesis in source leaves correlates with the down-regulation of P5CS genes. Leaf discs from four leaves having a different sink/source balance at the vegetative stage (60 DAS) were incubated for 4 h under continuous light with ¹⁵NH₄Cl (99%). (A) Metabolic route for ¹⁵NH₄ to proline and net ¹⁵N allocation to free amino acids. (B) Glutamine, glutamate, and proline net ¹⁵N labelling. (C) Net ¹⁵N allocation to proline.¹⁵N labelling detection, and absolute quantification of amino acids were performed by MS and UV detection. Values are the means ±SD of three independent biological replicates. Different letters indicate that mean values are significantly different between the different leaf ranks (P-value <0.05). (This figure is available in colour at JXB online.)