Do mitochondria provide the oxygen diffusion barrier in root nodules of Coriaria and Datisca?

Abstract

Root nodules of Coriaria Lindsay and Datisca Baill. display a unique anatomy in which the symbiotic vesicles radiate inwards towards a central vacuole. Use of the confocal microscope and the redox dye cyano-tetrazolium chloride demonstrates that the vesicles are the sites of reducing potential and that there is a sharp cut-off in reducing potential at the base of the vesicles. The use of the lipophylic cationic dye rhodamine 123 revealed a continuous blanket of mitochondria in this zone. This was verified by transmission electron microscope views of nodule cells. Further studies reveal that the mitochondrial layer also forms a discontinuous layer around the intercellular air spaces. The nodules of plants grown with root systems at 5 and 40 kPa O2 did not show any differences in the thickness of the mitochondrial layer. Microtubules are also radially arranged in these cells and mitochondria are likely to reach their position by moving along this radial framework.Key words: actinorhiza, mitochondria, nitrogen fixation, nitrogenase, nodule, oxygen protection.