THE FUSION OF SPERM CELLS AND THE FUNCTION OF MALE GERM UNIT (MGU) OFTOBACCO (NICOTIANA-TABACUM L.)

Sperm cells released from in vivo-in vitro grown pollen tubes of tobac co are associated in pairs and initially enclosed by the plasma membra ne of the pollen tube. When the sperm cells are placed together, using glass microinjector needles, in an enzymatic solution, up to half und ergo cellular fusion with subsequent nuclear fusion. The frequency of sperm cell fusion decreases with time during the elongation of the pol len tube, suggesting that mechanisms inhibiting self-fusion of sperm c ells may develop as the pollen tube elongates through the style toward the ovule. This tendency may play an important role in inhibiting fus ion of the two sperm cells inside the calcium-rich synergid where the male germ unit dissociates and sperm cells are transported to their ta rget cells - the egg and central cell.