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ToxB greatly reduces recognizable actin cables and actin patches. Untreated biological cells contain concentrated cortical structures, especially in buds, whereas treated biological cells show only weak diffuse staining even at ten times the exposure. The disappearance concerns actin filament organization and detectable F-actin, not necessarily destruction of the actin protein itself. actin monomer sequestration could leave substantial total actin present while eliminating most visible polymer.

Loss of actin cables should impair directed secretory-vesicle delivery and polarized cell growth; loss of actin patches should impair actin-dependent endocytosis. Disruption of the actomyosin machinery can also compromise cytokinesis. The rounded, poorly polarized appearance is consistent with these effects, but the images do not independently measure secretion, division rate or viability. A vehicle control and equal-exposure images are needed for quantitative fluorescence comparison; a longer exposure is useful for finding residual structures but prevents direct comparison of the displayed brightnesses.

Disrupting the dynamic actin network compromises processes required for sustained proliferation: endocytosis, directed delivery of cell membrane and cell-wall material, maintenance of polarized cell growth and successful cytokinesis. Failure of these actin-dependent functions can cause growth arrest and, under sufficiently damaging conditions, loss of viability. The altered sensitivity of actin mutants supports an actin-related mechanism, with their different assembly properties potentially changing the reserve of functional cytoskeleton.

A clear zone itself establishes failure to form a visible lawn, not necessarily death. biological cells might remain viable but fail to bud or divide while drug is present. Recovery after drug removal and subsequent colony formation would distinguish reversible arrest from killing. The experiment also does not identify which actin-dependent process first becomes limiting; matched measurements of trafficking, budding and division would be needed for that ordering.

Efficient and timely budding requires the normal actin network, but some initial polarized cell growth remains possible when visible actin filaments are greatly depleted. Around 40% of control biological cells have new buds by two hours, rising to nearly 60% by six hours. Drug-treated biological cells show almost no budding at two hours but roughly 15–20% at four to six hours, and the phase images confirm small buds despite loss of normal bright actin structures.

The result therefore supports a large delay and reduction, rather than an absolute block to every initiation event. Polarity cues or localized membrane-fusion machinery could remain spatially organized without normal long actin cables. The images and bud counts do not establish completion of a daughter-cell cycle, normal cytokinesis or indefinite proliferation. Residual actin filaments below detection remain an alternative contributor. This distinction between initial bud emergence and completion of growth was directly examined in a quiescence-exit study.^[ref]

Formation and growth of a daughter-cell bud. A visible bud is evidence of initial polarized cell growth but does not establish normal cytokinesis or long-term proliferative capacity.