However, analysis of deficiency symptoms following nutrient withdrawal and the approach used in this paper (analysis of nutrient mobilization from se- nescent leaves under conditions where nutrients are not lim- iting) represent fundamentally different experiments. The analysis of deficiency symptoms is done in stressed plants. Our study uses healthy plants undergoing natural senes- cence. Thus the different results obtained from these two types of studies could indicate that Cu, Fe, Mo and Zn are mobilized from leaves during natural senescence in healthy plants but that mobilization is affected by nutrient deficiency. Alterna- tively, species-specific differences in mobilization could also account for some of the differences observed between these two experimental approaches.