Rates of Pollen Tube Germination in Comparison with Flowering Seasons Marie Motahari and Sarah Broussard

Research Question Would the plants with the shortest flowering season have the fastest pollen tube germination rates? We hypothesized that they would, in order to increase the chance of fertilizing a flower before it dies.

Methods and Materials Humidity chambers were created by cutting a circle out of a coffee filter, placing it on the bottom of a petri dish, and adding a little bit of water to it. A straw was bent and placed on top of the coffee filter to act as a stand for the specimen. The specimen was pollen grains in a welled microscope slide with a 10% sucrose solution added to it.

Methods and Materials The three types of pollen grains used were blackberry, snowbell, and false garlic. Each specimen was placed in two petri dishes, labeled A and B, and left to germinate overnight. The next day we hooked a microscope up to the TV and put in a measurement slide, marking off every nanometer on a string of yarn. We then put our pollen slides into the microscope and measured three pollen tubes from each species on the TV screen using the yarn.

Results Blackberry A Blackberry B pollen tube #1 4.8 µm 5.7 µm   Blackberry B pollen tube #1 4.8 µm 5.7 µm pollen tube #2 2.8 µm 4.8µm pollen tube #3 5.6 µm 3.7 µm Snowbell A   Snowbell B pollen tube #1 4.5 µm 4.85 µm pollen tube #2 not enough pollen tubes 5.5 µm pollen tube #3 False Garlic A   False Garlic B pollen tube #1 5.5 µm 10 µm pollen tube #2 6.2 µm 10.5 µm pollen tube #3 11 µm

Results The Petri dishes with blackberries had a pretty moderate amount of pollen tube growth. The pollen tubes were not so close that we could not differentiate them from each other, but there were definitely a fair number of tubes growing. The average pollen tube length for blackberries is 4.57 micrometers.

Results The snowbells had the least amount of pollen tube growth. In fact, we were not able to find three measurable pollen tubes in either of the Petri dishes. The average pollen tube length for snowbells is 4.95 micrometers.

Results False garlic yielded the most pollen tubes. There were so many pollen tubes that they were stacked up on top of each other and we had a hard time finding unobstructed view of enough of them to measure. The average pollen tube length for false garlic is 9 micrometers.

Results The flowering season of blackberries lasts four months, from May to September. The average flowering season of false garlic is said, in places where it is more common, to be 2 months, April to May, as well as snowbell.

Measurement Slide

Blackberry

Snowbell

False Garlic

Discussion Our hypothesis was not supported by this experiment because false garlic and snowbell have the same growing season, but had growth rates at complete opposite ends of the spectrum. There are a few major possible errors, including that we did not know what which part of the reproductive cycle the flowers were at. For example, the snowbells could have had that little pollen tube growth simply because they were at the end of their period of dropping pollen, thus not as much pollen was left to make a bunch of pollen tubes. It could also be possible that the false garlic had so many pollen tubes because they were at the very peak of their pollen dropping phase.

Discussion Also, measuring with yarn has a lot of room for error. It must be done very carefully. We could have made mistakes in measuring. In the false garlic slides, the pollen tubes were so close together that we could have confused them and measured them wrong.

Special thanks to: Dr. Diane Byers, our Planting Science mentor. Dr. Allison Landry, our Botany instructor.

Sources http://www.pfaf.org/user/plant.aspx?latinname=Rubus+fruticosus Blackberry flowering season http://plants.usda.gov/factsheet/pdf/fs_nobi2.pdf False garlic flowering season http://en.m.wikipedia.org/wiki/Leucojum#section_1 Snowbell flowering season