Actin filament dynamics are dominated by rapid growth and severing activity in the Arabidopsis cortical array

Metazoan cells harness the power of actin dynamics to create cytoskeletal arrays that stimulate protrusions and drive intracellular organelle movements. In plant cells, the actin cytoskeleton is understood to participate in cell elongation; however, a detailed description and molecular mechanism(s) underpinning. lament nucleation, growth, and turnover are lacking. Here, we use variable-angle epifluorescence microscopy (VAEM) to examine the organization and dynamics of the cortical cytoskeleton in growing and nongrowing epidermal cells. One population of. laments in the cortical array, which most likely represent single actin. laments, is randomly oriented and highly dynamic. These. laments grow at rates of 1.7 mu m/s, but are generally short-lived. Instead of depolymerization at their ends, actin. laments are disassembled by severing activity. Remodeling of the cortical actin array also features. lament buckling and straightening events. These observations indicate a mechanism inconsistent with treadmilling. Instead, cortical actin. lament dynamics resemble the stochastic dynamics of an in vitro biomimetic system for actin assembly.