Interaction of gravity with other environmental factors in growth and development: an introduction.

The life of plants and other organisms is governed by the constant force of gravity on earth. The mechanism of graviperception, signal transduction, and gravireaction is one of the major themes in space biology. When gravity controls each step of the life cycle such as growth and development, it does not work alone but operates with the interaction of other environmental factors. In order to understand the role of gravity in regulation of the life cycle, such interactions also should be clarified. Under microgravity conditions in space, various changes are brought about in the process of growth and development. Some changes would be advantageous to organisms, but others would be unfavorable. For overcoming such disadvantages, it may be required to exploit some other environmental factors which substitute for gravity in some properties. In terrestrial plants, gravity can be replaced by light under certain conditions. The gravity-substituting factors may play a principal role in future space development.