Crossword Genius

Plant's lock-up bolt (5)

Ross

I believe the answer is:

lupin

I'm a little stuck... Click here to teach me more about this clue!

'plant's' is the definition.
The answer is an example.

'lock-up bolt' is the wordplay.
I cannot quite see how this works, but
'up' is present in the answer.
The remaining letters 'lin' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for lupin that I've seen before include "Garden plant of the pea family" , "Spiked flower" , "Plant with flowers on long spikes" , "Flower with spike of usually purplish-blue flowers" , "Flower called after wolf" .)

I've seen this clue in the Sydney Morning Herald.
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