THE ROLE OF CA2-TRANSDUCTION FOLLOWING FERTILIZATION IN FUCUS-SERRATUS( IN SIGNAL)

The marine brown alga Fucus serratus represents one of the few multice llular plant species in which the process of fertilization can be stud ied relatively easily. Fertilization marks the onset of a cascade of e vents associated with egg activation. Fertilization in Fucus serratus bears several superficial similarities to fertilization in several ani mal systems. The essential features of Fucus serratus egg activation a re compared with those of protostome and deuterostome animal systems. Ca2+ is required for egg activation in Fucus serratus and cytosolic [C a2+] changes can be observed in fertilizing eggs. However, these are s mall and variable in comparison with those occurring in deuterostomes, and fertilization can proceed normally in the absence of any global c ytosolic Ca2+ transients. A model for egg activation in Fucus serratus is presented, invoking a role for both Ca2+ influx and localized prop agation of the sperm signal around the plasma membrane by an as yet un identified mechanism. Polarity in Fucus serratus is acquired a conside rable time after fertilization and the role of cytosolic Ca2+ gradient s in the acquisition and expression of polarity is discussed. The prob lem of the signals associated with the onset of the cell cycle in the fertilized Fucus serratus egg is also addressed.