Calcium-induced sperm fusion in Zea mays L.

In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 mu m in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 mu m. Staining of sperm nuclei with 4', 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20-50 mu m from the tip. The Sperms are found no closer than 90 mu m to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid.