Arabidopsis will likely be an effective model organism for the study of nutrient mobilization during senescence particularly for macronutrients such as K, N, P and S. With the complete Arabidopsis genome sequence available, genes that could potentially be involved in nutrient mobilization can be identi- fied. It has recently become possible to identify loss-of-func- tion mutations in genes for which the sequence is known (Krysan et al. 1999).