Shout of support about beginnings of very unusual reproductive structure (5)
I believe the answer is:
ovule
'reproductive structure' is the definition.
(I know that ovule is a type of reproductive structure)
'shout of support about beginnings of very unusual' is the wordplay.
'shout of support' becomes 'ole' (I've seen this in another clue).
'about' is an insertion indicator.
'beginnings of' indicates taking the first letters (the beginning letters).
The initial letters of 'very unusual' is 'vu'.
'ole' enclosing 'vu' is 'OVULE'.
(Other definitions for ovule that I've seen before include "Egg cell" , "Part of plant ovary which becomes seed" , "Part of flower" , "Small body containing the female germ cell of a plant" , "Undeveloped seed" .)