Outflow movement during gamete discharge in Bryopsis plumosa (Caulerpales, Chlorophyta)

Abstract

Mine I., Yoshimatsu K., Kobanba A., Sekida S. and Okuda K. 2011. Outflow movement during gamete discharge in Bryopsis plumosa (Caulerpales, Chlorophyta). Phycologia 50: 363–369. DOI: 10.2216/10-66.1Light-induced gamete discharge in the caulerpalean alga Bryopsis plumosa was analyzed using video microscopy. Gametangia kept in darkness discharged gametes 7–8 min after they were exposed to light. The dimensions of gametangia continued to decrease until gamete discharge was initiated. When the apical papilla of a gametangium broke down to make a pore, gametes were explosively expelled from the gametangium through the pore. This was immediately followed by the moderate, continuous movement of the inner contents of the gametangium towards the pore, which we call outflow movement, resulting in the exhaustive evacuation of gametes from the gametangium. The velocity of outflow movement gradually decreased and continued for several tens of seconds. Outflow movement in the apical and middle portions of the gametangium was faster than that in the distal portion. When gametangia were cut to remove the apices at different times after exposure to light, the gametangia without apices also experienced outflow movement. Outflow movement occurred even in gametangia fixed with paraformaldehyde at time points between the beginning of light exposure and the initiation of gamete discharge. A mass of a material formed specifically in the gametangial vacuole was detected by histochemical staining. We discuss a possible relationship, referring to the connection between this material and the mechanisms by which the shrinkage of the gametangium and the outflow movement of gametes may be driven.