Editing Fertilisation (section)

===Pollen tube growth===
Unlike animal sperm which is motile, the sperm of most seed plants is immotile and relies on the [[pollen tube]] to carry it to the ovule where the sperm is released.<ref name="Duan et al 2014">{{cite journal |doi=10.1038/ncomms4129 |pmid=24451849 |title=Reactive oxygen species mediate pollen tube rupture to release sperm for fertilization in Arabidopsis |journal=Nature Communications |volume=5 |pages=3129 |year=2014 |last1=Duan |first1=Qiaohong |last2=Kita |first2=Daniel |last3=Johnson |first3=Eric A |last4=Aggarwal |first4=Mini |last5=Gates |first5=Laura |last6=Wu |first6=Hen-Ming |last7=Cheung |first7=Alice Y |bibcode=2014NatCo...5.3129D |doi-access=free }}</ref>  The pollen tube penetrates the [[Stigma (botany)|stigma]] and elongates through the extracellular matrix of the style before reaching the ovary.  Then near the receptacle, it breaks through the [[ovule]] through the micropyle (an opening in the ovule wall) and the pollen tube "bursts" into the embryo sac, releasing sperm.<ref name="Cheung-1995">{{cite journal |doi=10.1016/0092-8674(95)90427-1 |pmid=7634328 |title=A floral transmitting tissue-specific glycoprotein attracts pollen tubes and stimulates their growth |journal=Cell |volume=82 |issue=3 |pages=383–93 |year=1995 |last1=Cheung |first1=Alice Y |author-link1=Alice Cheung |last2=Wang |first2=Hong |last3=Wu |first3=Hen-Ming |doi-access=free }}</ref>  The growth of the pollen tube has been believed to depend on chemical cues from the pistil, however these mechanisms were poorly understood until 1995.  Work done on [[Nicotiana|tobacco plants]] revealed a family of [[glycoprotein]]s called TTS proteins that enhanced growth of pollen tubes.<ref name="Cheung-1995" />  Pollen tubes in a sugar free pollen germination medium and a medium with purified TTS proteins both grew.  However, in the TTS medium, the tubes grew at a rate 3x that of the sugar-free medium.<ref name="Cheung-1995" />  TTS proteins were also placed on various locations of semi [[in vivo]] pollinated pistils, and pollen tubes were observed to immediately extend toward the proteins.  Transgenic plants lacking the ability to produce TTS proteins had slower pollen tube growth and reduced fertility.<ref name="Cheung-1995" />