Yield plant ovule, say (4)
I believe the answer is:
cede
'yield' is the definition.
(I know that yield can be written as cede)
'plant ovule say' is the wordplay.
'plant ovule' becomes 'seed' (I've seen this in another clue).
'say' indicates a 'sounds like' (homophone) clue.
'seed' sounds like 'CEDE'.
(Other definitions for cede that I've seen before include "21 across" , "Allow" , "Surrender or grant" , "Yield or give up to another" , "Reluctantly give up" .)