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Abstract
The dynamics of cellular organelles reveals important information about their functioning.
The spatio-temporal movement patterns of vesicles in growing pollen tubes are controlled
by the actin cytoskeleton. Vesicle flow is crucial for morphogenesis in these cells
as it ensures targeted delivery of cell wall polysaccharides. Remarkably, the target
region does not contain much filamentous actin. We model the vesicular trafficking
in this area using as boundary conditions the expanding cell wall and the actin array
forming the apical actin fringe. The shape of the fringe was obtained by imposing
a steady state and constant polymerization rate of the actin filaments. Letting vesicle
flux into and out of the apical region be determined by the orientation of the actin
microfilaments and by exocytosis was sufficient to generate a flux that corresponds
in magnitude and orientation to that observed experimentally. This model explains
how the cytoplasmic streaming pattern in the apical region of the pollen tube can
be generated without the presence of actin microfilaments.