POSITION OF THE VEGETATIVE AND SPERM CELLS OF GERMINATING POLLEN GRAIN IN MAIZE (ZEA-MAYS L)

Maize pollen grains germinating on either defined media or fresh silks are described. The vegetative cell and sperm cells were distinguished clearly by size, shape and staining intensity. The positions of the sperm cells and that of the vegetative cell (tube nucleus), with respect to the pollen grain and the elongated pollen tube, were measured and expressed as its distance from the germ pore of the pollen grain. The relative position with respect to each other was also determined. Our results provide support that: 1) the position of sperm cells during early pollen germination is significantly variable; 2) the occurrence of sperm cells at several specific positions in the germinating pollen grain varies considerably between the inbred, B73, and the hybrid, Pearl and Honey; 3) there is good agreement in the behavior of in vivo and in vitro materials; 4) there is no physical association among the vegetative cell and the sperm cells during early maize pollen germination; 5) the size and shape of sperm cells inside the pollen tube vary; 6) there is no physical evidence to prove that the movement of sperm cells in the pollen tube is cell directed; and 7) the vegetative cell is the last of the three units to move into the pollen tube from the pollen grain.