Plant that's isolated deprived of nitrogen (4)
I believe the answer is:
aloe
'plant' is the definition.
(aloe is a kind of plant)
'isolated deprived of nitrogen' is the wordplay.
'isolated' becomes 'alone' ('alone' can be similar in meaning to 'isolated').
'deprived of' suggests deleting specific letters.
'nitrogen' becomes 'n' (N is the chemical symbol for nitrogen).
'alone' with 'n' taken away is 'ALOE'.
'that's' acts as a link.
(Other definitions for aloe that I've seen before include "Fleshy-leaved plant" , "shrub" , "O, ale with bitter plant" , "has a bitter taste" , "Succulent plant (may be bitter!)" .)