Needing to be done quickly in plant (4)
I believe the answer is:
rush
I believe this is a double definition.
'needing to be done quickly' is the first definition.
(as in a rush job)
'plant' is the second definition.
(rush is a type of plant)
'in' is the link.
(Other definitions for rush that I've seen before include "Sudden flow of liquid" , "Overcharge" , "Race" , "Lose no time" , "Stampede - water plant" .)