The Organization of mitochondria in growing hyphae of Neurospora crassa

Details of mitochondrial system organization and behavior in the tip of growing N. crassa hyphae and hyphal fragments were studied by means of cell-permeable mitochondria-selective probes in glucose- and sorbitol-containing media. It was shown that filamentous mitochondria concentrate in the 30-μm apical zone of growing hyphae and hyphal fragments independently of the carbon source. The mitochondrial assemblies propagate forward with elongation of hypha, split upon apical branching, and are formed de novo when branches are formed away from the growing tip. These activities resemble microtubule behavior. Co-staining with Mitotracker Red and Mitotracker Green revealed possible functional heterogeneity in subpopulations of mitochondria. It was proposed that the observed features are governed by the microtubular network, while the primary function of mitochondria was to sustain the growth rate. The organizing role of electrical gradients on the growing tip and their influence on mitochondrial and microtubular networks are discussed.