begins at the distal margin of the leaf and proceeds downward toward the petiole (Lohman et al. 1994, Weaver et al. 1998). Given the general pattern of Arabidopsis leaf senescence it is likely that nutrient mobilization would begin at the distal margins and that the nutrients would traverse the lower part of the leaf before exit- ing the leaf. If this is the case, analysis of nutrients in whole leaves midway through senescence might not accurately re- flect the efflux of nutrients from senescing tissue because nu- trients mobilized in the distal portion of the leaf may still be