Levels of Na and Mg do not appear to decrease in Arabi- dopsis leaves between 27 and 37 DAG suggesting that these metals are not targets of senescence-associated mobiliza- tion. Both metals are mobile in phloem (Bukovac and Wittwer
1957, Marschner 1995). Despite being phloem-mobile, Na does not appear to be mobilized from leaves in either Arabi- dopsis or wheat (Hocking 1994). Mg appears to be mobilized from leaves of soybean and wheat (Mauk and Noodén 1992, Hocking 1994) but not from pea (Marschner 1995) or Arabi- dopsis.