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Questions and Answers: 2015

Question: I was looking at the questions at this site and I saw one about pollen tubes. I've had a question …

• Question

  I was looking at the questions at this site and I saw one about pollen tubes. I've had a question about that,and decided to paste it here. What makes a plant’s pollen send out a pollen tube? What is the stuff, the material, on a flower’s stigma that makes a pollen grain send out a pollen tube? Is it water? I’m pretty sure it isn’t that because I’ve never seen pollen grains sending out pollen tubes in puddl

  Answer

  Dear pkbeep, when the pollen lands on a compatible stigma, there are several things required for it to germinate (as you noted, they do not germinate when they land in puddles). In some cases, the pollen grain must first hydrate, this accomplished by liquid present on the stigmatic surface. There are proteins, waxes, and lipids that are involved in signaling hydration and adhesion to the stigma and subsequent germination of the pollen grain. Germination is also thought to be regulated by specific polyphenol compounds. Therefore, a pollen grain will not germinate anywhere, but must experience the correct set of conditions. And those conditions are only met on stigmas of the same species (and, in some cases, in closely related species).