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Unlike other actin-binding proteins, actin depolymerizing factor (ADF) binds to both filamentous and globular actin, and causes the rapid depolymerization of actin filaments. ADF localizes to sites of active actin dynamics, including growing maize root hairs. ADF activity is regulated by a variety of stimuli implicated in affecting actin organization, such as pH changes, phosphorylation and polyphosphoinositides. Our current understanding of ADF’s role in regulating actin dynamics has been greatly enhanced through examination of the biochemical properties of plant ADFs. ADF depolymerizes actin filaments by a combination of severing activity and enhancing the rate of actin monomer dissociation from the pointed end. As a result, ADF-induced depolymerization creates a large pool of actin subunits. When the ends of actin filaments are uncapped, this pool is able to rapidly repolymerize. However, when filament ends are capped, repolymerization can not occur. Therefore, depending upon the presence of actin-filament capping factors, ADF either drives filament turnover or induces total depolymerization.

Microsporogenesis is an ideal system for studying cell division and the role of the cytoskeleton during higher plant development. Male meiosis in maize has been studied extensively using conventional cytological techniques, and more recently by fluorescence microscopy. The collection of 26 existing meiotic mutants can be grouped into six categories including: meiotic initiation, prophase chromosome pairing, chromosome morphology, chromosome segregation and cytokinesis, variable meiotic defects, and exit from meiosis. Using indirect immunofluorescence staining we have characterized the timing and nature of perturbations to the microtubule cycle in nine meiotic mutants. Several have microtubule disruptions that precede any other cytological abnormalities. For example, progression from a prophase microtubule array to a metaphase spindle is abnormal in the mutant dv1. Instead of converging to form focused poles, the metaphase spindle poles remain broad and divergent as in prometaphase. Two other mutants, ms17 and ms28, have defects including abnormal or multiple spindles, and cytokinetic failure that can be attributed to an excess of microtubules. The recessive mutation ameiotic1replaces meiosis I with a mitotic division. All features of these sporocytes, including chromosome behaviour, are typical of a somatic division. Surprisingly, a preprophase band predicts the future plane of division. These observations suggest that the wild type function of Ameiotic is to superimpose unique features of meiosis onto a mitotic division. One advantage of the microsporogenesis system is the availability of powerful genetic tools including transposon tagging. We have recovered several recessive meiotic mutants from Robertson’s Mutator lines. One mutation (dsy*)is similar to existing synaptic mutants and the other (aph1) has a novel phenotype with interesting effects on phragmoplast formation and positioning.