I’d imagine this will be as interesting to some you fellow Mirai disciples as it was to me. The TLDR is basically that auxin stimulates a decrease in the PH inside the cell, which loosens the cell wall, and allows it to blow up like a balloon as additional water is pumped into it.
This is interesting in the context of the maple pinching/internode lengthening debate, as one could imagine that by pinching the center of an opening shoot one would remove some of the auxin mediated expansion of the present plant cells, leaving individual cells smaller. With the cells not elongating to their full potential due to the removal of auxin mediated expansion it follows a smaller internode could result. Obviously, this is only conjecture, and not an attempt at a “gotcha” on Ryan, who has formulated his opinion based on far more practical experience than any of us could dream to achieve. I only bring it up to further a fascinating discussion, since there does seem to be disagreement between the “Bonsai Elite” on this point.