24 The Physiology of Tropisms

Abstract

Since the historic work of Darwin (1896), one of the driving forces in the field of plant physiology has been the study of tropisms. Tropisms are directed growth responses to environmental stimuli such as light, gravity, temperature (heat), and water. Thus, the tropism by the plant is an integrated response to a number of pieces of information concerning the status of the plant’s environment. Tropisms have been widely studied, largely because they are obvious outward evidence of the processing of information by the plant. Despite the great interest in tropisms by plant biologists during the past century, progress in this area has not been rapid. This can be partially attributed to the fact that many studies have been limited to observations of the final growth response of the organism as a consequence of the manipulation of the environmental stimulus. It seems clear that an understanding of the steps between the stimulus and the final growth response will require new approaches to the problem.

In recognition of this requirement for new approaches to understanding tropisms, and in recognition of the promise of Arabidopsis thaliana for genetics and molecular genetics, this plant was adapted as a model system for sensory physiology study slightly more than a decade ago. Since that time, research efforts have been directed toward the biophysical definition of tropisms in this model plant system and the development of genetic systems for their study. In this chapter, our goal is to describe the present state of information concerning tropisms in...