MICROTUBULES AND ORGANELLE MOVEMENTS IN RUST FUNGUS UROMYCES-PHASEOLI VAR-VIGNAE

Abstract

Direct visual observation and time lapse films of in vitro differentiating infection structures of the cowpea rust fungus U. phaseoli var. vignae revealed 3 categories of movement: general movement of cytoplasm, plus organelles, into the developing portion of the fungus during which the nuclei, in particular, maintained their characteristic position with remarkable constancy; relatively slow movements of various organelles such that they became displaced relative to one another and to the growing fungal tip; and erratic, rapid saltations of small organelles over short distances. Serial section ultrastructural analysis showed that microtubules were typically oriented 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 (< 2 .mu.m) and, in various parts of the cell, were often intimately associated with 3-6 nm diameter filaments of unidentified material. Interphase nuclei characteristically lacked microtubules emanating from their variously laterally or posteriorly located nucleus associated organelles, but were associated with groups of laterally placed microtubules. The correlations between the observed types of movement and the ultrastructure of the cells are discussed in terms of various models for organelle motility.