Cytoplasmic migrations and vacuolation are associated with growth recovery in hyphae of Saprolegnia, and are dependent on the cytoskeleton

Hyphae of Saprolegnia ferax recovered from intracellular acidification with variable degrees of apical vacuolation and migration of cytoplasm out of the apex, prior to apical refilling and resumption of growth. The response was not due to alkalinization, but was generalized to recovery from diverse growth inhibitors including procaine, latrunculin B and the kinase inhibitor 6-dimethylaminopurine. The vacuoles apparently arise from expansion and fusion of apical tubular vacuoles. This process is mediated by microtubules, since their disruption suppresses apical vacuolation. The shape of the vacuoles appears to be F-actin imposed, because their expansion is enhanced by F-actin disruption. The accompanying, often bidirectional, cytoplasmic migrations are independent of tip growth, require F-actin, and probably represent part of a hypothetical generalized cytoplasmic avoidance response.