In vitro double fertilization in Nicotiana tabacum (L.): polygamy comparedwith selected single pair somatic protoplast and chloroplast fusions

In vitro polygamy was studied mainly by using isolated sperm and central ce lls of tobacco in order to elucidate the mechanism that might be involved i n preventing in vivo polygamy. In 17.5% 4000 M.W. polyethylene glycol, only when two sperm cells were made close enough to each other and adhered to a female cell simultaneously was polygamy possible, If one sperm cell fused with the egg or central cell, within 30 min another sperm cell could not fu se with the same egg or central cell. Similar phenomena were found in selec ted single somatic cell fusion. When more than two protoplasts adhered to e ach other simultaneously, fusion was always successful; after two protoplas ts fused, within 30 min the fusion products could not fuse with another pro toplast under the same conditions. This comparative study revealed this cha racteristic to be shared by both sexual and somatic cell fusion. However, a fter cytoplasm reorganization was complete in the fusion product, it was po ssible fur the fusion product to fuse with the third protoplast. This: indi cates that the obstruction to additional fusion was present only during a c ertain period after the preceding fusion under certain condition. The possi ble reason for the effect is discussed.