However, gravitropism clearly is the most
robust tropism in roots as indicated by a number of
parameters (Kiss, 2000). For example, gravitropic
curvature as measured by the feedback system remains
linear without reaching a distinct plateau phase (Mullen
et al., 2000) while both red- and blue-light based
phototropism reach a plateaufollowing a linear increase
in response (Figure 3; see also Mullen et al., 2002; Kiss
et al., 2003).