Pleased Lou is working in the plant (9)
I believe the answer is:
'the plant' is the definition.
The answer is an example.
'pleased lou is working' is the wordplay.
'pleased' becomes 'glad' (similar in meaning).
'working' is an anagram indicator.
'louis' anagrammed gives 'iolus'.
'in' acts as a link.
(Other definitions for gladiolus that I've seen before include "Plant of iris family" , "Flower" .)