Figure 10.

Hypothetical model integrating the current knowledge about the role of auxin, NO, ROS, and AtCRK5 kinase in the root gravitropic response in Arabidopsis. Arrowheads indicate positive, blunt ends indicate negative regulation. Note that some of the interactions are only transient. Note that the effect of ROS, NO, and auxin on PIN2 endocytosis/turnover can be positive and negative depending on concentration and timing. For a detailed description see the text. NO—nitric oxide; ROS—reactive oxygen species; PIN2—PINOID 2 auxin efflux carrier; AtCRK5—Arabidopsis thaliana Calcium-Dependent Protein Kinase-Related Kinase 5.