Which of the following is not a part of the acid-growth hypothesis?

The acid growth hypothesis states that when the plants are exposed to auxin the cells will elongate and expand quickly at low pH. When auxin is introduced into the plants they cause the protons to be pumped out of the cells forming a proton pump across the cell membrane and thus lowers the pH which results in cell expansion. This acidifies the cell wall thus resulting in the breakage of cross-links due to the expansion of the cell wall.