The Enigmatic Metabolite Transport in Plant Mitochondria Lacking Proton Motive Force - news from Durum Wheat Mitochondria

Mitochondria play a central role in all aerobic eukaryotic cells, being the site of respiration and synthesis of ATP via Oxidative Phosphorylation (OXPHOS). According to the chemo-osmotic theory, this occurs bycoupling substrate oxidation by the respiratory chain with proton ejection in the intermembrane space [1,2], thus generatingan electrical membrane potential (ΔΨ), which is the main component in plant mitochondria [3], and the proton gradient (ΔpH), both components contributing to the overall Proton Motive Force (pmf) utilized for ATP synthesis [4]. Interestingly, pmf represents the driving force also for many protein-mediated transport activities across the Inner Mitochondrial Membrane (imm). In fact, the flux of hydrophilic solutes across the imm, that represents a diffusion barrier generally impermeable to charged and polar molecules, is facilitated and regulated by a large number of specific hydrophobic transport proteins, including carriers and ion-conducting channelsthat meet the complex metabolic demands. In fact, mitochondria provide, through the tri-carboxylic acid cycle, reducing equivalents for other compartments and carbon skeletons for biosynthesis of nucleotides, amino acids, fatty acids and vitamin cofactors, nitrogen assimilation, photorespiration, photosynthesis in C4 and CAM plants, utilization of carbon and nitrogen storage compounds during seed germination [3,5-7].