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

The response of plants to P sub(i) limitation involves interplay between root uptake of P sub(i), adjustment of resource allocation to different plant organs and increased metabolic P sub(i) use efficiency. To identify potentially novel, early-responding, metabolic hallmarks of P sub(i) limitation in crop plants, we studied the metabolic response of barley leaves over the first 7d of P sub(i) stress, and the relationship of primary metabolites with leaf P sub(i) levels and leaf biomass. The abundance of leaf P sub(i), Tyr and shikimate were significantly different between low Pi and control plants 1h after transfer of the plants to low P sub(i). Combining these data with super(15)N metabolic labelling, we show that over the first 48h of P sub(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 sub(i) stress, appearing to modulate partitioning of soluble sugars between amino acid and carboxylate synthesis, thereby limiting leaf biomass accumulation when external P sub(i) is low.