Hypergravity prevents seed production in Arabidopsis by disrupting pollen tube growth.

How tightly land plants are adapted to the gravitational force (g) prevailing on Earth has been of interest because unlike many other environmental factors, g presents as a constant force. Ontogeny of mature angiosperms begins with an embryo that is formed after tip growth by a pollen tube delivers the sperm nucleus to the egg. Because of the importance to plant fitness, we have investigated how gravity affects these early stages of reproductive development.

Plant secondary metabolism in altered gravity.

Plans by the space program to use plants for food supply and environmental regeneration have led to an examination of how plants grow in microgravity. Because secondary metabolic compounds are so important in determining the nutritional and flavor characteristics of plants-as well as making plants more resistant to biotic and abiotic stresses-their responses to altered gravity are now being studied. These experiments are technically challenging because temperature, humidity, atmospheric composition, light, and water status must be maintained around the plant while simultaneously altering the g-load, either in the free-fall of orbital spacecraft or on a centrifuge rotor.

Gravity control of growth form in Brassica rapa and Arabidopsis thaliana (Brassicaceae): Consequences for secondary metabolism.

How gravity influences the growth form and flavor components of plants is of interest to the space program because plants could be used for food and life support during prolonged missions away from the planet, where that constant feature of Earth's environment does not prevail. We used plant growth hardware from prior experiments on the space shuttle to grow Brassica rapa and Arabidopsis thaliana plants during 16-d or 11-d hypergravity treatments on large-diameter centrifuge rotors. Both species showed radical changes in growth form, becoming more prostrate with increasing g-loads (2-g and 4-g).

Plant reproductive development during spaceflight.

Reproductive development in microgravity has now been studied in a variety of plants; Arabidopsis, Brassica, and Triticum have been especially well studied. Earlier indications that gravity might be required for some stage of reproductive development have now been refuted. Nevertheless, the spaceflight environment presents many unique challenges that have often compromised the ability of plants to reproduce.