Plant Biology

The Earth is host to more than 400,000 documented species of plant life. In turn, our planet depends upon these plants to nurture and sustain all living things. Plants play a critical role in the complex food web. Powered by light from the sun, C02 from the air, and nutrients from the soil, plants pass on this energy to the life forms that consume them. And for the human species, plants bring aesthetic pleasure, delighting the senses with their beauty and variety.

On Earth, plant roots as a rule grow downward toward gravity, while stems grow up and away from gravity, a phenomenon known as gravitropism.

By studying plants in microgravity on board spacecraft, biologists seek to understand how plants respond to gravity. Also, plants respond to environmental stimuli such as light, temperature, water, wind, and magnetic or electric fields. These responses are masked on Earth by the overriding response of plants to gravity. In addition, any strategy that visualizes a long-term sustained human presence in space absolutely requires the ability to continuously grow and reproduce various plant species over multiple generations, for food and controlled environmental life support systems.

Figure 1-19. Knight's experiment showing the angle of orientation with respect to gravity assumed by roots and shoots of seedlings when they are rotated in a horizontal plane. Seedlings, originally pinned vertically (in A), grow in the direction of the resultant of the gravitational and centrifugal force vectors (in B). When the clinostat in oriented vertically and slowly rotates (in C), during a complete turn of the disc, the gravitational force acts laterally from all directions. As the plant is kept rotating, it orients itself in the horizontal direction, with no gravity-dependent curvature in roots and shoots. Adaptedfrom Bfurstedt (1979).

Figure 1-19. Knight's experiment showing the angle of orientation with respect to gravity assumed by roots and shoots of seedlings when they are rotated in a horizontal plane. Seedlings, originally pinned vertically (in A), grow in the direction of the resultant of the gravitational and centrifugal force vectors (in B). When the clinostat in oriented vertically and slowly rotates (in C), during a complete turn of the disc, the gravitational force acts laterally from all directions. As the plant is kept rotating, it orients itself in the horizontal direction, with no gravity-dependent curvature in roots and shoots. Adaptedfrom Bfurstedt (1979).

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