Figure 7.

Hypothetical Model for the Role of ABA and Ethylene in Regulating Root Growth in Arabidopsis.

(A) In the absence of ethylene, one way for ABA to inhibit root growth is by signaling through the ETR1 response pathway. Because this pathway is also regulated by ethylene, mutations in the pathway interfere with both ABA and ethylene signaling.

(B) In the presence of ethylene, ABA is unable to use this pathway; thus, mutations that increase ethylene synthesis confer an ABA-insensitive root phenotype.