In Arabidopsis, N levels are 85.4 % lower in senescent leaves than in pre-senescent leaves. This degree of mobiliza- tion is similar to that observed in other organisms such as wheat, soybean, pine and pea (Mauk and Noodén 1992, Hock- ing 1994, Marschner 1995, Nieminen and Helmisaari 1996).