Figure 10.

Extended model of the transduction chains for gravitropism and phototropism and their putative interconnections via the tonic feedback loop. The mutation geo-10 confers hypergravitropism (Ootaki et al., 1995). The gravitropic and the phototropic transduction chains are linked through the tonic feedback loop consisting of three elements: (a) a tonic enhancer (+, dashed line), which exerts a light-mediated stimulation of gravitropism; (b) the negative regulator geo-10, and (c) a tonic inhibitor (-, dashed line), which acts on the phototropic transduction chain. Irradiation with blue light (450 nm) causes strong tonic enhancement and strong tonic inhibition that are symbolized by large numbers. Near-UV light (370 nm) causes only moderate tonic effects (small numbers). Vectorial interactions of the transduction chains are indicated by solid lines. Further explanations in the “Discussion.” The other symbols and mutants are as in Figure 1.