Clare Robke-Blog Post #7

How do flowering plants (angiosperms) like our Brassica oleracea plants reproduce? Well, we know that humans reproduce sexually, after all that is how we are all here and how I am writing this blog post right now. But sexual reproduction isn't just for people and animals. Flowering angiosperm plants like our broccoli reproduce this way too! An angiosperm is a plant that has flowers and produces seeds enclosed within a carpel. Just like people, these plants have male and female reproductive organs. The male part is called the stamen and the female part is called the carpel/pistil. The stamen contains the filament, which is the long, slender stalk, and the anther, which is at the top of the filament and is where pollen grains (sperm) are produced. The carpel is composed of an ovary, a style, and a stigma. Inside the ovary, there are one or more ovules that act kind of like a woman's eggs and grow into a seed when fertilized. Using these parts, plants reproduce through the transfer of pollen to the female ovules in a process called pollination. The pollen can reach the carpel by pollinators such as insects, birds, bats, water, wind, or even the plants itself. After pollination occurs, fertilization happens and the ovules grow into seeds within a fruit. This is how a plant baby is born!

This is a normal, everyday look at a flower from our broccoli plant. It is what the world sees when looking at this specific angiosperm. Even without a microscope, you can clearly view a few of the reproductive organs including the stigma and the anthers. The petals are also obviously visible as they surround the plant to protect the important reproductive parts.

This is our Brassica oleracea under the microscope. Now, we can see much more clearly both the male and female reproductive parts like the stigma, style, and anthers. The anthers are on top of the filaments, but because of the angle the filaments aren't as visible. A plant such as this one is considered "perfect" because it has both a stamen and a carpel. The majority of angiosperms are perfect in this way, which is a huge factor that contributes to the species being the considered the most successful of all plant groups. Having both male and female parts means they have pollen as well as flowers/fruits. The flowers are able to attract insects and this allows better transportation of pollen. Angiosperms also go through something called double fertilization, which helps the plant.

This image shows 6 stamen and a single carpel, however we will focus on the stamen for now. As I have mentioned, the stamen is the entire male reproductive anatomy of flowering plants. It is fairly simple and only includes two parts: the filament and the anther. The filament is a slender stalk that supports the anther. The anther is the more important male part. This oval-shaped structure on the end of the filament is where the male gametophyte, known as pollen, is produced.

The photo above shows part of the carpel, or female reproductive anatomy, of our broccoli flower. The carpel consists of three parts: stigma, style, and ovary. The ovary is at the base and supports a long, tube-like style, which is topped by a small, circular stigma. This image focuses only on the stigma and style. The stigma is the little ball on top. Since this is the part of the carpel where pollen must land and germinate, it is sticky to make sure the pollen will adhere. The style is a long, slender stalk that connects the stigma and the ovary. As the pollen grain germinates on the stigma, it creates a pollen tube through the entire length of the style. The pollen tube grows out of the pollen grain and creates a tunnel from the stigma to the ovary.

Here you can see the flower with nearly all of its parts stripped away. The sepals, petals, and stamens are all gone. The stigma and style are still present, but the main focus of the image is on the ovary. The ovary is the larger, base portion of the carpel that is connected to the sepals. The ovary contains many ovules which develop into seeds once they are fertilized. With the ovary sliced open as it is in the picture, you can see some of the ovules inside, but there is also a more clear one located slightly to the left of the carpel.