Cytochrome c links energy metabolism, respiration and plant growth

WELCHEN ELINA; IGOR, FLOREZ-SARASA; MANSILLA, NATANAEL; MIQUEL RIBAS-CARBÓ; GONZALEZ, DANIEL H.

Congreso; 8vo International Conference in Plant Mitochondrial Biology; 2013

Photosynthesis and respiration must be coordinated with other metabolic pathways to provide the energy required for cell functioning. An open question is what happens when cyanide-sensitive respiration is affected. We studied double homozygous Arabidopsis mutant plants that contain very low cytochrome c (CYTc) levels. We have demonstrated that CYTc is essential at early stages of plant development and is required for Complex IV stability. Mutant plants show a delay in development, with lower biomass content. Surprisingly, oxygen isotope fractionation measurements indicated that in vivo COX pathway activity is not affected in these plants, while AOX pathway activity is reduced. Photosynthetic parameters are similar in mutant and WT plants. CYTc mutants also show a decreased respiratory quotient (RQ) and altered AN/RCO2 ratio in the light, suggesting an alteration in carbon balance. Indeed, mutant plants accumulate starch and soluble sugars at higher levels than WT during diurnal cycle, due to an increase in net starch synthesis during the day. Contrary to previous thoughts, lower CYTc levels produce a decrease in alternative respiration, possibly to favor the use of carbon through the energy producing pathway. This may cause a rearrangement of metabolism that shifts the use of assimilated carbon towards starch at the expense of growth. Our results suggest that CYTc would constitute a cornerstone in the regulation of energy metabolism, respiration and plant growth.