Physode formation in embryos of Phyllospora comosa and Hormosira banksii (Phaeophyceae)

Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic constituent of eggs and zygotes of the Australasian fucoids Ho rmosira banksii (Turner) Decaisne and Phyllospora comosa (Labillardiere) C Agardh. Light and transmission electron microscopy in conjunction with the actin inhibitors cytochalasin and latrunculin and the Golgi disrupter Brefe ldin were used to investigate physode biogenesis in Hormosira and Phyllospo ra zygotes and embryos. Our results show that physodes are formed in the pe rinuclear region of the cell. Contrary to many early reports, no evidence w as found that physode genesis is associated with chloroplasts. Instead, the Golgi apparatus and the endoplasmic reticulum are implicated in physode fo rmation. Physodes are produced in large quantities around the nucleus just before periods of active wall deposition, particularly during rhizoid initi ation and crosswall formation. Subsequently, they move from their central l ocation to the sites of wall deposition.