Company register initially available in part of plant (7)
I believe the answer is:
corolla
'part of plant' is the definition.
(I've seen this before)
'company register initially available' is the wordplay.
'company' becomes 'co' (abbreviation).
'register' becomes 'roll' (list of names).
'initially' suggests taking the first letters.
The initial letter of 'available' is 'a'.
'co'+'roll'+'a'='COROLLA'
'in' acts as a link.
(Other definitions for corolla that I've seen before include "Part of a flower" , "part of plant" , "Flower's petals collectively" , "Internal whorl of a flower" , "Whorl of flower petals" .)