We studied the effect of reducing the levels of the mitochondrial electron carrier cytochrome c (CYTc) in Arabidopsis thaliana. Plants with CYTc deficiency have delayed growth and development, and reach flowering several days later than the wild-type but with the same number of leaves. CYTc-deficient plants accumulate starch and glucose during the day, and contain lower levels of active gibberellins (GA) and higher levels of DELLA proteins, involved in GA signaling. GA treatment abolishes the developmental delay and reduces glucose accumulation in CYTc-deficient plants, which also show a lower raise in ATP levels in response to glucose. Treatment of wild-type plants with inhibitors of mitochondrial energy production limits plant growth and increases the levels of DELLA proteins, thus mimicking the effects of CYTc deficiency. In addition, an increase in the amount of CYTc decreases DELLA protein levels and expedites growth, and this depends on active GA synthesis. We conclude that CYTc levels impinge on the activity of the GA pathway, most likely through changes in mitochondrial energy production. In this way, hormone-dependent growth would be coupled to the activity of components of the mitochondrial respiratory chain.

Institute of Developmental and Molecular Biology of Plants Plant Molecular Physiology and Biotechnology Group Heinrich Heine Universität Universitätsstraße 1 40225 Düsseldorf Germany Cluster of Excellence on Plant Sciences 40225 Düsseldorf Germany

Instituto de Agrobiotecnología del Litoral Cátedra de Biología Celular y Molecular Facultad de Bioquímica y Ciencias Biológicas Universidad Nacional del Litoral 3000 Santa Fe Argentina

Laboratory of Growth Regulators Centre of the Region Haná for Biotechnological and Agricultural Research Institute of Experimental Botany AS CR Faculty of Science Palacký University Šlechtitelů 27 CZ 78371 Olomouc Czech Republic

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