seeds have everything it needs to start growing, just water will do.

The round "leaves" are the plant´s reservatory, they go yellow as the reservatory is over, anyway you can feed the plant, the round leaves will stay green.
I´ve seen that in a hydroponic DWC system, plants that still have that reservatory doesn´t suffer at water changes, but plants without that reservatory tends to start going down pretty fast as they got out of the nutrient solution.


In this pics you can see(i hope so) that the reservatory is already used, this plant had some root problems(it is fine now)
Im not an expert, just telling you what i´ve read and seen.
Hope it helps.