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I of young, lateral roots grown under iron deficiency, whereas the femcyanide reductase (termed the standard reductase) was thought to be constitutively expressed in a11 root cells. However, more recent studies do not support this view. Both ferricyanide and Fe (II1) chelate reductases vIere found to increase approximately 2-fold under iron-deficiency conditions ir1 PM purified from tomato (Buckhout et al., 1989). PM from roots of iron-sufficient and iron-defic: cent plants contain Fe (II1) chelate reductases with similar characteristics (Holden et al., 1991), thus lending no support to the concept of the induction of a nove1 reductase in resporse to iron deficiency. The amplification of Fe (II1) chelate recluctase observed in PM isolated from iron-deficient plants, likely involves increased expression of Fe (1II) chelate reductase isoforms in expanding root epidermal PM. Thus, the Fe (II1) chelate reductase either is being …