Cellular morphogenesis in land plants and brown algae is typically a slow process. However, elongation of the zygote of the brown alga Dictyota dichotoma changes its shape in a 90 second burst from a sphere to an elongated spheroid.
The elongation can be parthenogenetically triggered by inducing membrane depolarisation (high potassium seawater) and calcium influx (ionomycin). Bogaert et al. show that the fast elongation is accomplished by forces generated by F-actin and myosin, regulated by cytoplasmic calcium concentrations, and by secretion during elongation lowering the antagonistic force.
Bogaert, K. A., Beeckman, T., & De Clerck, O. (2017). Egg activation-triggered shape change in the Dictyota dichotoma (Phaeophyceae) zygote is actin–myosin and secretion dependent. Annals of Botany, 120(4), 529–538. https://doi.org/10.1093/aob/mcx085