Chapter 1 Phototropism and Gravitropism in Plants

Abstract Light and gravity are two of the most important environmental parameters affecting plant growth and development. To maximize available light and nutrients, plants orient their stems toward the direction of illumination and away from the gravity vector, and, conversely, orient their roots away from light and toward gravity. In plant organs, there may be a competition between gravity (gravitropism) and light (phototropism). At the same time, the tropistic signaling and/or responses induced by both stimuli may be independent processes that coexist, or they may modulate each other. Our limited knowledge of the interaction of these tropistic stimuli is due to the ubiquitous nature of gravity on earth, which makes it difficult to study a “pure” effect of light without the interference of gravity. However, during the past decade, significant advances have been made in our understanding of gravity and light signal transduction pathways by using mutants and novel techniques for genome-wide analysis. Thus, both unique and common elements in the signaling and response pathways of both tropisms have been identified.