Logistics of Intracellular Transport Required for Cell Wall Assembly

In plants, cellular growth requires the assembly of extensive amounts of new cell wall surface. The targeted deposition of building material through exocytosis - cell wall polymers, enzymes and membrane material - is therefore a crucial regulatory feature in plant development. The spatial and temporal regulation of the delivery of cargo vesicles to the target surfaces are poorly understood. Spatio-temporal image correlation spectroscopy (STICS) was used to quantify the intracellular dynamics of secretory vesicles and of the actin arrays in pollen tubes - rapidly and polarly growing plant cells. The dynamic profiles were used to validate mathematical models for vesicular trafficking. Boundary conditions were the expanding cell wall (Fig.1A) and the actin array whose shape was obtained by imposing a steady state and constant polymerization rate of the actin filaments (Fig.1B). The model correctly predicted the vesicle flow patterns in different types of pollen tubes and provides an explanation for flow dynamics in cellular regions devoid of actin cytoskeleton. It will serve as a basis for understanding how pollen tubes are able to regulate their morphogenetic pattern, for example when responding to a directional trigger by changing the growth direction (Fig.1C).