Question

epinasty is caused by

Answer 1

Epinasty is caused by ethylene that is released by the leaves when the roots are flooded...

Answer 2

Epinasty is a perplexing behavior seen during the flooding of roots of plants.  Leaf cells on the top part of the leaf and maybe especially the leaf stem outgrow the bottoms ones and the leaf drops from a horizontal to a more vertical position.  Epinasty is caused by ethylene that is released by the leaves when the roots are flooded.  Flooded roots make ACC, the precursor to ethylene, and this is transported up the xylem stream to the leaf where it is converted to the gas hormone.