This Report is a "Best of Wendy Langhans" Report.
During allergy season , I sometimes wonder if pollen grains have their own navigation system . If that’s true, then their map for the Santa Clarita Valley must have a fluorescent orange locator pin labeled “Wendy’s nose”. (Thank goodness for antihistamines.)
But locating my nose is not pollen’s true mission; it’s true mission is reproduction. The first stage of that mission is called pollination , the “transfer of pollen from the anther to the female stigma”. (To see an illustration of the parts of a flower, click here .) Once a grain of pollen lands on the stigma’s sticky surface, the second stage, known as fertilization, begins. During this second stage, the pollen grain’s male reproductive cell (which carries the male genetic material) must find its way to the female reproductive cell, which is located deep inside the ovary.
It’s a long journey from the stigma down the style to the ovule. How does the genetic material physically get to where its going and how does it navigate along the way?
Let’s start with how it physically gets there. Each grain of pollen contains two nuclei. One nucleus is for sexual reproduction; the second nucleus grows a pollen tube. This pollen tube, which functions like a straw, provides a pathway to the egg. To visualize this, picture an ear of corn covered with of corn silk. Each strand of corn silk  contains a pollen tube. (To watch a short video about pollen tubes, click here .)
And how does the pollen tube know which direction to grow? This remains an open area of research. However, scientists are looking for biochemical signals, chemicals produced in the ovary, that attract and direct the growth of the pollen tube. In corn , for example, a peptide known as ZmEA1 may play a role in attracting the pollen tube.
So flowers produce navigational chemicals that help pollen grains complete their reproductive mission. Now if only there were a chemical that would navigate them away from my nose.
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