Plant Responses to Simulated Microgravity

Green plants are essential for the survival of human beings and other living organisms on earth and in space. During the past three decades, space has been explored by manned space missions and much information has been obtained on the survival of earthly organisms in space. Much attention has been directed to the study of the behavior and survival of living organisms in space, particularly under microgravity conditions. In general, plants are extremely sensitive to environmental factors such as light or gravity. Plant response to gravity has been an important subject of study in plant physiology for a long time. Like other tropistic responses, gravitropic responses in plants consist of three stages—namely, (1) gravity perception, (2) transformation of the gravitational stimulus, and (3) gravitropic response. In roots, the mechanism of graviperception is basically understood. However, it is not yet well understood in shoots, stems, and coleoptiles. A major difficulty in the study of gravimpism is the fact that plants are constantly exposed to the 1-G condition on earth. For over a century, attempts have been made to compensate the 1-G vector. The most widely used method is the use of the clinostat. A standard clinostat consists of a plant container rotating around a horizontal axis at 2–3 rpm. This chapter describes the advantages of this so-called three-dimensional clinostat for the simulation of microgravity conditions for plant seedlings and presents the results of some experiments with rice seedlings.