The Regulation of Root Growth in Cress Seedlings by Light and Gravity

Abstract

Horizontal growth of seedling roots of Lepidium sativum L. cv. Curled is sensitive to white light with a photon flux density as low as 7.5 μEinsteins m⁻² S⁻¹. Inhibition of growth is positively correlated with light intensity. Roots growing in the vertical plane are much less sensitive to light. The light inhibition of horizontal root growth can be overcome by the application of an axial force. The effects of light and axial force are reversible. Although geotropic responsiveness is not dependent on exposure to light, there is evidence that light induces a heightened geosensitivity. The results are discussed in relation to the counter-current theory of the regulation of root growth.