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Some cell membrane delivery and fusion must continue in the biological cells whose buds actually grow, but it need not use normal long-range cable transport. secretory vesicles can move by molecular diffusion or other non-directed motion and be preferentially captured, tethered and fused where a surviving polarity cue concentrates the relevant vesicle docking machinery. Spatial selectivity can therefore reside in the destination rather than in directed travel over the entire route. Less efficient delivery is consistent with delayed budding and small buds.

Short residual actin tracks could also contribute; the experiment does not prove that every actin filament is absent. Neither bud shape nor Con-A staining directly measures vesicle trajectories or fusion events. Tracking secretory vesicles together with a membrane-fusion reporter and a polarity marker would distinguish directed runs from molecular diffusion followed by localized capture, with expression and imaging controls for reporter effects. Random arrival with selective vesicle docking is a published mechanistic proposal for this physiological context, rather than a demonstrated trajectory in the present images.^[ref]

There is no evidence for substantial lipid mixing during the cold preincubation. The trace begins near its low-fluorescence baseline when warming starts; a substantial pre-existing dilution of the dyes would already have raised that baseline. Nevertheless, vesicle docking or trans-SNARE complex formation can accumulate while the later membrane-rearrangement step remains slow. Absence of dequenching does not mean that the vesicles have had no interaction.

Growth concentrated at a selected part of the biological cell surface. Spatial selection can be controlled at transport, vesicle docking or fusion rather than only by directed vesicle motion.

Vesicle docking brings a transport vesicle into close, stable association with its target membrane before membrane fusion. Recognition factors and SNARE proteins help organize the contact. Docking and fusion are experimentally distinct: a carrier can remain attached without exchanging its internal contents with the target compartment. Reconstituted liposomes bearing appropriate SNARE proteins allowed such docked intermediates to be distinguished from subsequent fusion. ^[ref]

Vesicle trafficking moves membrane and cargo between cellular compartments through transport carriers. Cargo selection and budding are followed by targeting, vesicle docking and membrane fusion. A carrier from the endoplasmic reticulum can deliver newly synthesized proteins to the Golgi apparatus, while other carriers retrieve resident components. Directional transport maintains distinct compartments despite continual membrane exchange; it depends on selective recognition rather than random mixing. ^[ref]