Line of plants in border region initially brought into question (8)
I believe the answer is:
hedgerow
'line of plants' is the definition.
'in border region initially brought into question' is the wordplay.
'in border' becomes 'edge' ('edge' can be a synonym of 'border'. I am not sure about the 'in' bit.**).
'initially' indicates taking the first letters.
'brought into' means one lot of letters goes inside another.
'question' becomes 'how' (I've seen this in other clues).
The first letter of 'region' is 'r'.
'edge'+'r'='edger'
'edger' inserted inside 'how' is 'HEDGEROW'.
(Other definitions for hedgerow that I've seen before include "Bushy boundary" , "Line of shrubs as barrier" , "Field boundary" , "natural fence" , "Living boundary between fields" .)