F-ACTIN REDISTRIBUTIONS AT THE DIVISION SITE IN LIVING TRADESCANTIA STOMATAL COMPLEXES AS REVEALED BY MICROINJECTION OF RHODAMINE-PHALLOIDIN

Microinjection of rhodamine-phalloidin into living cells of isolated T radescantia leaf epidermis and visualisation by confocal microscopy ha s extended previous results on the distribution of actin in mitotic ce lls of higher plants and revealed new aspects of actin arrays in stoma tal cells and their initials. Divisions in the stomatal guard mother c ells and unspecialised epidermal cells are symmetrical. Asymmetrical d ivisions occur in guard mother precursor cells and subsidiary mother c ells. Each asymmetrical division is preceded by migration of the nucle us and the subsequent accumulation of thick bundles of anticlinally or iented actin filaments localised to the area of the anticlinal wall cl osest to the polarised nucleus. During prophase, in all cell types, a subset of cortical actin filaments coaligns to form a band, which, lik e the preprophase band of microtubules, accurately delineates the site of insertion of the future cell wall. Following the breakdown of the nuclear envelope, F-actin in these bands disassembles but persists els ewhere in the cell cortex. Thus, cortical F-actin marks the division s ite throughout mitosis, firstly as an appropriately positioned band an d then by its localised depletion from the same region of the cell cor tex. This sequence has been detected in all classes of division in Tra descantia leaf epidermis, irrespective of whether the division is asym metrical or symmetrical, or whether the cell is vacuolate or densely c ytoplasmic. Taken together with earlier observations on stamen hair ce lls and root tip cells it may therefore be a general cytoskeletal feat ure of division in cells of higher plants.