Save key that opens plant (6)
I believe the answer is:
rescue
'save' is the definition.
(rescuing is a kind of saving)
'key that opens plant' is the wordplay.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'that opens' means one lot of letters goes inside another (some letters open a gap in others).
'plant' becomes 'rue' (type of shrub).
'esc' going within 'rue' is 'RESCUE'.
(Other definitions for rescue that I've seen before include "Save from peril" , "Pull from danger" , "Free - recovery" , "Deliver from harm" , "Retrieve" .)