Nitrogen Source for Somatic Embryogenesis - The form of nitrogen has a marked effect on somatic embryogenesis. In carrot, NH+₄ has a promotive effect on SE regeneration. In fact, induction of SEs in carrot occurs only when about 5 m mol/kg of cell fresh weight NH+ * is present in the cells. This level of endogenous NH+ ₄ is reached with only 2.5 m mol/l of exogenous level of NH+₄, while 60 m mol/l NO-₃ is needed for the same. Therefore, the presence of a low level of NH+₄(in carrot 10 m mol/l is optimal) in combination with NO-₃ is required for SE regeneration. In carrot,NH+₄ is essential during SE induction, while SE development occurs on a medium containing NO-₃ as the sole nitrogen source.