Intercellular transport across pit-connections in the filamentous red alga Griffithsia monilis

Intercellular nutrient and signal transduction are essential to sustaining multicellular organisms and maximizing thebenefits of multicellularity. It has long been believed that red algal intercellular transport of macromolecules is preventedby the protein-rich pit plug within pit-connections, the only physical connection between cells. Fluorescein isothiocyanate-dextran and recombinant green fluorescence protein (rGFP) of various molecular sizes were injected into vegetativecells of Griffithsia monilis using a micromanipulator, and intercellular transport of the fluorescent probes was examined.Pit-connections were found to provide intercellular transport of tracers at rates comparable to plasmodesmata in otherorganisms. The time necessary for the transport to an adjacent cell was dependent on the molecular size and the directionof the transport. Fluorescent dextran of 3 kDa was transported to adjacent cells in 1–2 h after injection and migratedto all cells of the filament within 24 h, but fluorescent dextran of 10–20 kDa took 24 h to transfer to neighboring cells. Themigration occurred faster towards adjacent reproductive cells and to apical cells than basally. Fluorescent tracers above40 kDa and rGFP was not transported to neighboring cells, but accumulated near the pit plug. Our results suggest thatpit-connections are conduit for macromolecules between neighboring cells and that these size-specific conduits allowintercellular communication between the vegetative cells of red algae.