摘要
Double fertilization is a specific characteristic of angiosperms,in which two sperm cells fuse with the egg and central cell respectively[1].Different from that of animals,the two sperm cells of angiosperms have lost their motility.Therefore,to fulfill the double fertilization,the two immobile sperm cells have to be sent to the female games by a specific structure,the pollen tube.Upon landing on the stigma of the pistil,the pollen grain germinates and devel-
Double fertilization is a specific characteristic of angiosperms, in which two sperm cells fuse with the egg and central cell respec- tively [1]. Different from that of animals, the two sperm cells of angiosperms have lost their motility. Therefore, to fulfill the double fertilization, the two immobile sperm cells have to be sent to the female games by a specific structure, the pollen tube. Upon landing on the stigma of the pistil, the pollen grain germinates and devel- ops the pollen tube. The pollen tube then elongates in the way of tip growth through the transmitting tract along the style. Subse- quently, the pollen tube orientates to the micropyle of the ovule, and enters the ovule finally. When the pollen tube reaches the receptive synergid cell in an embryo sac, it bursts and releases two sperm cells to the region close to the egg cell and central cell. Soon one of the sperm cells fertilizes the egg cell to produce an embryo, while the other fuses with the central cell to produce endosperm [2,3]. During this process the pollen tube actually acts as a one-way specific train to the destination of the female gamete for unique passenger, the sperm cells.
