Proteomic Analysis Infers Optimized ATP-Production in Guard Cell Mitochondria

Guard cells are highly specialised leaf cells which regulate leaf transpiration and carbon fixation. As such, they are instrumental in balancing water use efficiency and photosynthetic activity. This unique function of guard cells requires them to quickly accumulate solutes for ATP-dependent stomatal opening, but how this affects mitochondrial energy metabolism remains elusive. Using cell-type-specific affinity purification of Arabidopsis thaliana guard cell and mesophyll cell mitochondria, we aim at unravelling the enzymatic configuration of guard cell mitochondria in order to provide a first glance at the metabolic properties of these specialised organelles. When compared to their mesophyll cell counterparts, the use of alternative substrates for NADH production, a shift away from non-proton pumping respiratory enzymes, and a lower NADH re-oxidation rate suggest a specialised mode of ATP production in guard cell mitochondria. In addition, a lowered abundance of the mitochondrial import machinery also indirectly implies lower protein turnover rates in these organelles.