Unique actin and microtubule arrays co-ordinate the differentiation of microspores to mature pollen in Nicotiana tabacum

The complex cellular events that occur during development of the male gamet ophyte of higher plants suggest a role for the cytoskeleton. This investiga tion has revealed that unique microtubule arrays mediate events that occur during microspore development; both actin and microtubule arrays have impor tant roles during the asymmetrical microspore mitosis and unique actin arra ys mediate events that occur during early pollen development, Migration of the nucleus to the generative pole during cellular polarization of the micr ospore is mediated by a microtubule cage that encloses the nucleus. Nuclear position at the generative pole is maintained by an actin net that tethers it to the pole prior to the asymmetrical mitosis. During entry into mitosi s, the microtubule cage becomes modified and transforms into the asymmetric al mitotic spindle, Actin is localized within the region of the mitotic spi ndle and in the phragmoplast, following mitosis, actin networks enclose fir st the generative cell and then the vegetative nucleus. These actin network s function during migration of the generative cell and vegetative nucleus t oward the centre of the pollen grain. Mature pollen contains a dense cortic al actin meshwork and a disc-shaped microtubule array enclosing the generat ive cell. The functional importance of the unique actin and microtubule arr ays is verified by their targeted disruption with specific cytoskeletal inh ibitors, which disrupt normal development and cellular morphology. In summa ry, these data provide evidence that the co-ordinated reorganization of uni que actin and microtubule arrays is an essential determinant of microspore and pollen development.