Plant science's leading character featured in talk (7)
I believe the answer is:
parsley
'plant' is the definition.
(parsley is a kind of plant)
'science's leading character featured in talk' is the wordplay.
'leading character' indicates taking the first letters.
'featured in' indicates putting letters inside.
'talk' becomes 'parley' (to parley is to talk with an enemy).
The first letter of 'science' is 's'.
's' inserted inside 'parley' is 'PARSLEY'.
(Other definitions for parsley that I've seen before include "Herb for garnishing" , "Cow -, fool's - and stone - are all plants" , "Use the herb sparely" , "plant used in cooking" , "Culinary herb" .)