PROGRESSION OF SPERMATIAL NUCLEAR DIVISION REQUIRES CALCIUM INFLUX DURING FERTILIZATION OF THE RED ALGA PALMARIA SP

During fertilization of the red alga Palmaria sp. (Palmariales), the p rophase-arrested nucleus of the uninucleate spermatium resumes its div ision after direct attachment of the spermatium to the trichogyne of a carpogonium. Treatments that reduce Ca2+ influx inhibit the progressi on of spermatial nuclear division. The ratio of the number of spermati a released from prophase arrest (those in metaphase to binucleate stag es) to the total spermatia attached to trichogynes was significantly r educed by incubating the spermatia in the culture solution having low Ca2+ concentration. Similar inhibition was observed by addition of eit her inorganic (La3+ and Co2+) Or organic (nifedipine and tetramethrin) Ca2+ channel inhibitors to the culture solution containing 10 mM Ca2. These results indicate that the prophase / metaphase transition of s permatial nuclear division requires an influx of Ca2+ and suggest that Ca2+ acts as a second messenger to the mechanical or chemical stimulu s that initiates mitotic progression of spermatia in this alga.-