Poster: Tropisms

Abs # 657: Phytochrome and tropisms in Arabdidopsis roots

Presenter:	Correll, Melanie J., correlmj@muohio.edu
Authors	Correll, Melanie J. (A)   Mullen, Jack L. (B)   Kiss, John Z. (A)
Affiliations:	(A): Department of Botany, Miami University Oxford, OH 45056 (B): Department of Biology, Indiana University Bloomington, IN 47405

Gravity and light both influence the form of a plant. For example, primary roots of Arabidopsis grow in the direction of the gravity vector (positive gravitropism), curve away from blue or white light (negative phototropism), and curve towards red light (positive phototropism). The blue/white-light-induced negative phototropism in roots is primarily controlled by the blue-light-adsorbing photoreceptors, the phototropins (phot1, phot2). The red-light-induced positive phototropism is primarily controlled by two of the red-light-adsorbing photoreceptors, phytochromes A and B. Phytochromes are also involved in gravitropism as red light can disrupt the gravitropic responses of Arabidopsis seedlings. To study gravitropism and phototropism in Arabidopsis roots we have used a feedback stage to constrain the root tip to a particular position (vertical for light treatments and horizontal for gravity treatments). Specifically, we have studied the positive gravitropism and positive phototropism (red light) in roots of phyA, phyB, phyAB and WT (Ler) seedlings using this rotatable feedback system. Roots from the double mutant, phyAB, are severely reduced in gravitropic curvature compared to WT, but roots from phyA respond similarly to WT. For red-light-induced positive phototropism, curvature begins at a fluence rate of approximately 0.1 µmol m^-2 s^-1 (~10° of total curvature) and this response saturates at a fluence rate of approximately 1 µmol m^-2 s^-1 (~40° of total curvature). Studies are in progress to determine the effects of far-red light on positive phototropism of Arabidopsis roots.