Microtubules and organelle movements in the rust fungus Uromyces phaseoli var. vignae

Direct visual observation and time lapse films of in vitro differentiating infection structures of the cowpea rust fungus Uromyces phaseoli var. vignae revealed three categories of movement: a) general movement of cytoplasm, plus organelles, into the developing portions of the fungus during which the nuclei, in particular, maintained their characteristic position with remarkable constancy, b) relatively slow movements of various organelles such that they became displaced relative to one another and to the growing fungal tip, and c) erratic, rapid, saltations of small organelles over short distances. Serial section ultrastructural analysis showed that microtubules were typically orientated parallel to the direction of cytoplasm migration. Simple statistical analyses showed that the microtubules were non-randomly associated with mitochondria but only rarely associated with lipid droplets or microbodies. All microtubules were typically short (less than 2 micrometer) and, in various parts of the cell, were often intimately associated with 3 to 6 nm diameter filaments of unidentified material. Interphase nuclei characteristically lacked microtubules emanating from their variously laterally or posteriorly located NAOs (nucleus associated organelle) but were associated with groups of laterally placed microtubules. The correlations between the observed types of movement and the ultrastructure of the cells discussed in terms of various models for organelle motility.