Throughout the evolution of plants on land, there is a trend in reduction of the gametophyte. Pollen is the microgametophyte in both gymnosperms and angiosperms. Recall that conifer pollen has four cells and inflated air sacs that serve as wings. In angiosperms, the pollen lacks wings and is reduced to only two cells: the generative cell and the tube cell.
Below are two microgametophytes. On the left is pine pollen, a gymnosperm microgametophyte. On the right is lily pollen, an angiosperm microgametophyte.
Which cells were lost in angiosperm pollen (present in gymnosperms)?
What are the functions of the tube cell and the generative cell?
The stigma contains compounds that trigger the production of the pollen tube. This trigger can be as simple as a high concentration of carbohydrates, which we can mimic by using corn syrup. However, sometimes there are extra triggers present on a stigma, such as lipids or calcium. For the next part of the lab, you are going to develop and conduct an experiment to test the best method for stimulating production of pollen tubes.
Questions to consider:
- How will you determine what “best” means? Is it number of pollen grains to produce a pollen tube? Average length of pollen tube?
- How will you standardize other variables? Will you have controls?
- Will you have replicates within your experiment? Will other scientists be able to replicate your work in future experiments?
Record your experimental design and steps of the process of science on "Pollen Tube Germination Experimental Design" below.