Revolutionary part of plant used in cigar (7)
I believe the answer is:
cheroot
'cigar' is the definition.
(cheroot is a kind of cigar)
'revolutionary part of plant' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary**).
'part of plant' becomes 'root' (I've seen this before).
'che'+'root'='CHEROOT'
'used in' is the link.
(Other definitions for cheroot that I've seen before include "One smoked" , "Cigar cut at both ends" , "With both ends cut off squarely, is smoked" , "'Cigar, square at both ends (7)'" , "Variety of cigar" .)