Fibrous vacuole associated organelles (FVAOs) in the Florideophyceae: a new interpretation of the ‘appareil cinétique’

Structures first reported in Bonnemaisonia hamifera spermatangia to be non-emergent flagella (appareil cinétique) were found in Polysiphonia harveyi spermatangia and Dasya baillouviana tetrasporangia and are interpreted to be fibrous vacuole associated organelles (FY AOs) involved in early stages of fibrous vacuole formation. The FVAO appears to arise from ER and to initiate formation of the fibrous vacuoles characteristic of florideophycean spermatangia and spores. It is also hypothesized that the organelle may process the vacuolar contents in some manner and/or modify the vacuolar membrane, thereby enabling this membrane to ultimately fuse with the plasma membrane. Although FY AO function was not completely determined, its morphology is well defined and consistent and leads to the conclusion that the FVAO is a discrete organelle unique to red algae.