The missing link: inter-organellar connections in mitochondria and peroxisomes?

Abstract

In their review of mitochondrial redox biology in plants, Graham Noctor et al. [ 1 Noctor G. et al. Mitochondrial redox biology and homeostasis in plants. Trends Plant Sci. 2007; 12: 125-134 Abstract Full Text Full Text PDF PubMed Scopus (375) Google Scholar ] discuss the role of stromules (stroma-filled plastid tubules [ 2 Kohler R.H. et al. Exchange of protein molecules through connections between higher plant plastids. Science. 1997; 276: 2039-2042 Crossref PubMed Scopus (517) Google Scholar , 3 Natesan S.K.A. et al. Stromules: a characteristic cell-specific feature of plastid morphology. J. Exp. Bot. 2005; 56: 787-797 Crossref PubMed Scopus (132) Google Scholar ]) in the transport of metabolites and proteins between cellular compartments. In contrast to their comment that no similar extensions have been described in mitochondria, we would like to draw attention to previous research showing that such protuberances are also common to both mitochondria and peroxisomes in plants (Figure 1) ([ 4 Cutler S.R. et al. Random GFP:cDNA fusions enable visualization of subcellular structures in cells of Arabidopsis at high frequency. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 3718-3723 Crossref PubMed Scopus (753) Google Scholar , 5 Logan D.C. et al. ADL2a, like ADL2b, is involved in the control of higher plant mitochondrial morphology. J. Exp. Bot. 2004; 55: 783-785 Crossref PubMed Scopus (76) Google Scholar , 6 Muench D.G. Mullen R.T. Peroxisome dynamics in plant cells: a role for the cytoskeleton. Plant Sci. 2003; 164: 307-315 Crossref Scopus (25) Google Scholar , 7 Sparkes I.A. et al. AtPEX2 and AtPEX10 are targeted to peroxisomes independently of known endoplasmic reticulum trafficking routes. Plant Physiol. 2005; 139: 690-700 Crossref PubMed Scopus (59) Google Scholar ]; and see movies by Professor Brian E.S. Gunning FRS available from http://www.plantcellbiologyondvd.com). Indeed, such membranous extensions have been reported to be emanating from mitochondria in chick spinal cord [ 8 Grainger F. James D.W. Mitochondrial extensions associated with microtubules in outgrowing processes from chick spinal cord in vitro. J. Cell Sci. 1969; 4: 729-737 PubMed Google Scholar ], from hydrogenosomes in trichomonad species [ 9 Benchimol M. et al. Morphogenesis of the hydrogenosome: an ultrastructural study. Biol. Cell. 1996; 87: 197-205 Crossref PubMed Google Scholar ] and from the apicoplasts of Sarcocystis, an apicomplexan parasite [ 10 Tomova C. et al. New comprehension of the apicoplast of Sarcocystis by transmission electron tomography. Biol. Cell. 2006; 98: 535-545 Crossref PubMed Scopus (25) Google Scholar ]. These membranous extensions are thus a feature common to endosymbiosis-derived organelles and peroxisomes. Mitochondrial redox biology and homeostasis in plantsNoctor et al.Trends in Plant ScienceMarch, 2007In BriefMitochondria are key players in plant cell redox homeostasis and signalling. Earlier concepts that regarded mitochondria as secondary to chloroplasts as the powerhouses of photosynthetic cells, with roles in cell proliferation, death and ageing described largely by analogy to animal paradigms, have been replaced by the new philosophy of integrated cellular energy and redox metabolism involving mitochondria and chloroplasts. Thanks to oxygenic photosynthesis, plant mitochondria often operate in an oxygen- and carbohydrate-rich environment. Full-Text PDF