Temporal development of the barley leaf metabolic response to P i limitation

The response of plants to P limitation involves interplay between root uptake of P , adjustment of resource allocation to different plant organs and increased metabolic P use efficiency. To identify potentially novel, early-responding, metabolic hallmarks of P limitation in crop plants, we studied the metabolic response of barley leaves over the first 7 d of P stress, and the relationship of primary metabolites with leaf P levels and leaf biomass. The abundance of leaf P , Tyr and shikimate were significantly different between low Pi and control plants 1 h after transfer of the plants to low P . Combining these data with N metabolic labelling, we show that over the first 48 h of P 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 stress, appearing to modulate partitioning of soluble sugars between amino acid and carboxylate synthesis, thereby limiting leaf biomass accumulation when external P is low.