Positioning the Root Elongation Zone Is Saltatory and Receives Input from the Shoot

In the root, meristem and elongation zone lengths remain stable, despite growth and division of cells. To gain insight into zone stability, we imaged individual Arabidopsis thaliana roots through a horizontal microscope, and used image analysis to obtain velocity profiles. For a root, velocity profiles obtained every 5 min over 3 h coincided closely, implying that zonation is regulated tightly. However, the position of the elongation zone saltated, by on average 17 μm every 5 min. Saltation was apparently driven by material elements growing faster and then slower, while moving through the growth zone. When the shoot was excised, after about 90 minutes, growth zone dynamics resembled those of intact roots, except that the position of the elongation zone moved, on average, rootward, by several hundred microns in 24 h. We hypothesize that mechanisms determining elongation zone position receive input from the shoot

Brief of \u3ci\u3eAmici Curiae\u3c/i\u3e Law Professors and Economists in Support of Petitioner in \u3ci\u3eSouth Dakota v. Wayfair, Inc., et al.\u3c/i\u3e

Amici are professors of tax law and economics at universities across the United States. As scholars and teachers, they have considered the economic consequences of this Court’s decision in Quill Corp. v. North Dakota, 504 U.S. 298 (1992), and have concluded that Quill’s dormant Commerce Clause holding should be overruled. Amici join this brief solely on their own behalf and not as representatives of their universities. A full list of amici appears in Appendix A