The Irt1 Gene Is Responsible for Most of the Iron

The irt1 gene is responsible for most of the iron uptake activity in roots (Vert et al., Plant Cell 14 [2002]: 1223-33) . To determine the specificity of the irt1 transporter in Arabidopsis plants, researchers measured the concentration of manganese, zinc, copper, and cobalt contained in wild-type and irt1-1 mutant plants. What conclusions about irt1 specificity can you draw from the data in the accompanying figure?

A) Under iron-deficient conditions, irt1 is highly specific for iron.
B) Under iron-deficient conditions, irt1 is important for the transport of iron and copper.
C) irt1 is important for the transport of iron and copper independent of iron concentration.
D) Under iron-deficient conditions, irt1 is necessary for the transport of zinc, manganese, and cobalt.
E) irt1 participates in the transport of iron, zinc, manganese, and cobalt independent of iron concentration.