Graduate pens two articles in plant (6)
I believe the answer is:
banana
'plant' is the definition.
(banana is a kind of plant)
'graduate pens two articles' is the wordplay.
'two articles' means two substitutions for 'article'.
'graduate' becomes 'ba' (someone with a Bachelor of Arts degree).
'pens' indicates putting letters inside.
'article' becomes 'an' (indefinite article).
'article' becomes 'an' (indefinite article).
'an'+'an'='anan'
'ba' enclosing 'anan' is 'BANANA'.
'in' acts as a link.
(Other definitions for banana that I've seen before include "Fruit with soft, sweet flesh" , "Fruit led by prohibition" , "Fruit item" , "plant" , "One out of hand" .)