Poster: Tropisms

Abs # 674: An Arabidopsis mutant with altered regulation of leaf inclination

Presenter:	Mullen, Jack L, jmullen@bio.indiana.edu
Authors	Mullen, Jack L (A)   Weinig, Cynthia  (B)   Hangarter, Roger P (A)
Affiliations:	(A): Indiana University, Department of Biology (B): University of Minnesota, Department of Plant Biology

Arabidopsis, a rosette plant, forms leaves near to the ground. This causes the plant to be vulnerable to shading by neighbors. One mechanism to avoid such shading is the regulation of leaf inclination, such that leaves can be raised to more vertical orientations to prevent neighboring leaves from growing over them. We have found that rosette leaves move to more vertical orientations when placed in the dark and reorient to more horizontal inclinations when replaced in white light. This response is mediated primarily through phytochromes A and B, though there is also a blue light component to the movements. In addition, rosette leaves of Arabidopsis are gravitropic, with set-point angles between 90° and 180°, which affects the equilibrium orientation of leaves for a given light environment. In order to better understand this regulation of leaf positioning, we have isolated a mutant with altered regulation of leaf orientation. In white light the leaves of the mutant are more vertical than wild type. However, the mutant changes its leaf inclination in a light-dependent manner, and the leaves are also gravitropic. Therefore, it appears that mutation alters the set-point angle rather than impairing the sensing of environmental cues. Further characterization of this mutant should provide insights into the interactions among signaling pathways involved in controlling lateral organ orientation. [This work was supported by the National Aeronautics and Space Administration through grant no. NCC 2-1200.]