What is the highest pressure at which plants can survive?
See Effect of very high pressure on life of plants and animals (2012).

Judging from the fact that all the living creatures we have examined, both animals (tardigrades and Artemia) and plants (Ptychomitrium, Venturiella and white clover) were alive after exposure to 7.5 GPa, it was suggested that most of the proteins of those creatures which unfolded at the early stage of the compression remain principally unchanged after exposure to the very high pressure of 7.5 GPa. It was also suggested that the unfolding of proteins was completely reversible up to 7.5 GPa.
The maximum hydrostatic pressure applied to all the living specimens investigated in the present experiments corresponds to that in the upper mantle, at the depth of 180 km from the surface of the earth.

So survival of plants at 75,000 times atmospheric pressure is possible. In this experiment the exposure times were 30 minutes and 1 hour for the plants and 13 hours for the animals.