How does photorespiration modulate leaf amino acid contents? A dual approach through modelling and metabolite analysis

Abstract

Abstract The aim of this work was to establish the quantitative impact of photorespiration on leaf amino acid contents. Attached leaves of wheat and potato were incubated for 30–40 min under defined conditions in which net CO 2 uptake ( A ) was manipulated by irradiance, ambient CO 2 or ambient O 2 . The incubated portion of the leaf was sampled by a rapid‐quench method and photorespiratory flux ( v o ) was modelled from the measured rate of net CO 2 uptake. In both wheat and potato, the ratio between glycine and serine showed a strong positive correlation with v o . Aspartate and alanine correlated negatively with v o but glutamate and glutamine showed less clear relationships. In potato, glutamate and glutamine did not correlate clearly with either A or v o . In wheat, glutamine showed a general increase with A but no relationship with v o , whereas 2‐oxoglutarate contents correlated positively with v o and negatively with A . As a result, glutamine : glutamate and glutamine : 2‐oxoglutarate increased with net CO 2 uptake in wheat, observations that are attributed primarily to imperfect and variable coupling between the supply of NH 3 in primary nitrogen assimilation and the associated delivery of 2‐oxoglutarate to the chloroplast. A simple theoretical analysis is used to illustrate the potentially marked impact of primary nitrogen assimilation on leaf glutamine, even against a background of high rates of photorespiratory ammonia recycling.