This idea was first proposed by David Rayle and R. Cleland in 1970. IAA stimulates proton excretion. These proteins transport protons from the protoplast into the wall. Auxin probably first binds to a receptor molecule and this complex then actives the pump. ATP stimulated acidification is observed very quickly after auxin treatment.
Auxin stimulates transcription and translation.
The proton effect is short-lived. Cell elongation stops 30-60 minutes after acidification. Continuous elongation requires longer term metabolic changes such as protein synthesis. C. Wall synthesis occurs . As the cell grows cell wall synthesis will need to occur.