It could be N def, or not enough light getting to them leaves. Another option is the plant is self triming the older ineffcient leaves. How tall is the entire plant? is it flowering? What kind of Lights?
I don't see any evidence of any burning whatsoever so I would think that it is N-def. Start out small and see how your plant reacts over time, the affected leaves may not fully recover but new leaves should be a nice green a few days to a week after feeding.