Temporal development of the barley leaf metabolic response to Pi limitation

The response of plants to P-i limitation involves interplay between root uptake of P-i, adjustment of resource allocation to different plant organs and increased metabolic P-i use efficiency. To identify potentially novel, early-responding, metabolic hallmarks of P-i limitation in crop plants, we studied the metabolic response of barley leaves over the first 7d of P-i stress, and the relationship of primary metabolites with leaf P-i levels and leaf biomass. The abundance of leaf P-i, Tyr and shikimate were significantly different between low Pi and control plants 1h after transfer of the plants to low P-i. Combining these data with N-15 metabolic labelling, we show that over the first 48h of P-i limitation, metabolic flux through the N assimilation and aromatic amino acid pathways is increased. We propose that together with a shift in amino acid metabolism in the chloroplast a transient restoration of the energetic and redox state of the leaf is achieved. Correlation analysis of metabolite abundances revealed a central role for major amino acids in P-i stress, appearing to modulate partitioning of soluble sugars between amino acid and carboxylate synthesis, thereby limiting leaf biomass accumulation when external P-i is low.