Ralitza Alexova, Clark J. Nelson and A. Harvey Millar
Why have we done this research?
The response of plants to Pi limitation involves a complex set of processes including root uptake of Pi, adjustment of resource allocation to different plant organs, and increased metabolic Pi use efficiency. There has been considerable transcript profiling studies looking for key elements in the plant response, our aim was to complement this by attempting to identify early-responding, metabolic hallmarks of Pi limitation and place this in the context of primary metabolism.
We studied the metabolic response of barley leaves over the first 7 days of Pi stress, and the relationship of primary metabolites with leaf Pi levels and leaf biomass. Changes in the abundance of leaf Pi, cofactors (FAD, NAD), Tyr, and shikimate were significant 1 h after transfer of the plants to low Pi. Combining these data with 15N metabolic labeling, we show that over the first 48 hours of Pi limitation metabolic flux through the N assimilation, photorespiratory and aromatic amino acid pathways are increased.
What do we think it means?
We propose that there is a shift in amino acid metabolism in the chloroplast and a need to restore the energetic and redox state of the leaf following an instantaneous change in Pi availability. Correlation analysis of metabolite abundances revealed a central role for major amino acids in Pi stress, appearing to modulate partitioning of soluble sugars between amino acid and carboxylate synthesis, which may play a role in limiting leaf biomass accumulation when external Pi is low.