Figure 7.

ABP1 mediates fast protoplast swelling, and TIR1 or other receptor candidates are important for hypocotyl growth. The model highlights that osmotically driven protoplast expansion is dependent on H⁺ pump activity, K⁺ influx, and water uptake. This fast ABP1-mediated response is triggered by IAA, PEO-IAA, and auxinole. IAA- and 5-F-IAA-induced hypocotyl growth are dependent on turgor pressure and cell wall (CW) loosening, processes regulated by TIR1 and putative other auxin receptor proteins.