Plant juice (3)
I believe the answer is:
sap
'plant juice' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sap that I've seen before include "Undermine the tree juice" , "Juice; energy" , "Liquid that circulates in plants" , "Fluid in plant stems" , "Watery substance in plants" .)