The short answer to the question about the effect of auxin (etc)
on hypocotyl elongation in Arabidopsis is yes, they do respond.
In our lab we looked at the effect of IAA on hypocotyl segments
in a series of ethylene related mutants. The main problems are
encountered when you try to manipulate the hypocotyls as they
crush very easily. We published in Annals of Botany 68, 56-61
if that is of any use. For short (18h) incubation we used a
buffered 2% sucrose solution (including the relevent test chemical).
Feel free to email me with any questions.
Institute of Biological Sciences
awb at aber.ac.uk