Plant Growth

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The plant in this timelapse is a quick-growing variety of Brassica rapa developed by Paul Williams at the University of Wisconsin and commonly called Wisconsin Fast Plants. They are widely used in classrooms and in research, because they have a very short generation time and can be grown at a high density in a small space under fluorescent light. Brassica rapa is in the mustard family, and is closely related to broccoli; the clusters of flower buds look like tiny broccoli stalks.

A 7 x 3 panorama was taken every 15 minutes for 26 days using a Canon PowerShot G10 mounted on an Epic Pro.

Cotyledons

The first leaves to emerge are seed leaves, or cotyledons; they are present in the embryo inside of the seed before it sprouts, and they are different in shape from the true leaves that develop as the plant grows. Cotyledons are important because they photosynthesize and generate the raw materials for new leaf growth.

Watch a snaplapse of cotyledon development.

Stinkbugs

Marmorated stinkbugs appear briefly on the plants at various times and places. They are a recently introduced pest that damages fruit and vegetable crops and enters buildings to overwinter. Because of this behavior, they became an accidental part of the timelapse. They are responsible for the bending of young plants early in the video. Watch the following snaplapse at a quarter speed to see the stinkbugs.

Watch a snaplapse of stinkbugs.

Plant movement

Timelapse reveals the movements of the plants as they grow. They are not growing in a straight line, but rather wiggling or circling about a central point. This behavior is called circumnutation. Charles Darwin studied movement in plants extensively, and documented circumnutation in 320 different plant species. Circumnutation is especially pronounced and important in vines, which must search their environment for supports to twine around, and it may help other species find patches of sunlight. Studies of plants grown in space have shown that tiny movements occur in plants never exposed to gravity. When these plants were exposed to simulated gravity in a centrifuge, circumnutation greatly increased, suggesting that gravity is an important trigger for plant movement.

Watch a snaplapse of circumnutation.

As the plants get bigger, they often fall over. Their narrow, weak stems are caused by the very high density of plants and light levels that are lower than direct sunlight. The plants are growing tall rather than stout stems to outcompete their neighbors for light, but end up with stems that are too weak to support their flowers and fruit and are vulnerable to bending by stinkbugs. The shallow root system caused by a small amount of soil may also lead to instability. After a plant falls over, it corrects the direction of its growth and bends its stem to continue growing up. This behavior is made possible by its ability to sense and respond to gravity.

Watch a snaplapse of plants correcting their growth after falling over.

Reproduction

The flowers of Brassica rapa have both male structures, which make pollen, and female structures, which develop into pod-like fruits containing seeds. Pollination is the transfer of pollen from the male structures to the female structures. While this transfer can take place within a flower, plants of this species recognize and reject their own pollen. Therefore, seeds and fruits only develop when pollen comes from a different plant. Because these plants were grown indoors in the absence of pollinating insects, the only fruits that developed came from flowers that bumped into flowers from another plant.

Watch a snaplapse of fruit development.

Caterpillars

Eggs of cabbage white butterflies, Pieris rapae, were introduced after the plants started flowering. The eggs are on a few small pieces of waxed paper placed on leaves. The caterpillars are tiny when they hatch, but grow quickly as they eat leaves and flowers.

Watch a snaplapse of caterpillars.

Classroom activity

The following worksheet may be used to guide classroom discussion as students explore plant growth and movement in the timelapse video.

File:Fast Plants worksheet.pdf

File:Fast Plants worksheet notes for instructor.pdf