The Redistribution of Radioactivity in Geotropically Stimulated Hypocotyls ofHelianthus annuusPretreated with Radioactive Calcium

Abstract

The purpose of this research was to study the movement of ⁴⁵Ca in geotropically stimulated hypocotyls of Helianthus annuus. Six-day old seedlings fed with ⁴⁵CaCl₂ were placed horizontal for 1, 2, or 3 hours. The ⁴⁵Ca accumulated more in the upper half of the hypocotyl than in the lower half, particularly after three hours. Geotropic stimulation under nitrogen causes no significant difference between the two halves. The role of this differential accumulation of Ca in geotropic curvature is discussed.