Dog had got into plant (6)
I believe the answer is:
shadow
'dog' is the definition.
(I've seen this before)
'got into plant' is the wordplay.
'got' becomes 'had' ('have' can be a synonym of 'get').
'into' is an insertion indicator.
'plant' becomes 'sow'.
'had' put into 'sow' is 'SHADOW'.
'had' is the link.
(Other definitions for shadow that I've seen before include "Follow - dark patch" , "Partial or complete darkness" , "Sort of boxer - dog" , "It's cast when light is blocked" , "Dark shape (on the Opposition front bench?)" .)