CAFFEINE INHIBITION OF CYTOKINESIS - EFFECT ON THE PHRAGMOPLAST CYTOSKELETON IN LIVING TRADESCANTIA STAMEN HAIR-CELLS

The distribution of microtubules and actin microfilaments during caffe ine-induced inhibition of cell plate formation has been studied in liv ing Tradescantia stamen hair cells. Previous studies have shown that c affeine allows cell plate initiation but prevents its completion, resu lting in binucleate cells. In the present study, confocal microscopy o f cells microinjected with fluorescent brain tubulin or phalloidin, an d cultured in the presence 5 mM caffeine, revealed that the initiation and early lateral expansion phase of the phragmoplast occur normally. However, caffeine completely inhibits the formation of the cytoskelet al torus which occurs in untreated cells during the late stages of cel l plate and phragmoplast expansion. Caffeine further causes the disint egration of the incomplete cell plate. The results allow us to disting uish two phases in cell plate and phragmoplast growth: the initiation and early expansion phase, which is not affected by caffeine, and the late lateral expansion phase, which is completely inhibited in the pre sence of caffeine. Also in this study, the use of a high phalloidin co ncentration has revealed structural detail about the actin microfilame nts involved in cell plate formation: microfilaments are observed that link the expanding edge of the phragmoplast with the cortical divisio n site. In addition, cortical actin patches are observed within the ac tin depleted zone that might play a role in guidance of phragmoplast a nd cell plate expansion.