Expressions of iron uptake genes in roots are affected by long-distance signals both in non-graminaceous and in graminaceous plants.
Iron, one of the essential elements in plants, exists in soil in almost unavailable form for uptake from roots. Non-graminaceous plants (strategy I) and graminaceous plants (strategy II) have different mechanisms for iron uptake in the roots, though the structure and the function of some of the proteins related to iron uptake, such as IRT, FRO, bHLH, which are conserved between strategy I and II plants. Cis-acting elements of iron uptake genes are also conserved among them. In Arabidopsis, tobacco, tomato and pea, the induction of iron uptake in roots is thought to be regulated by unknown systemic long-distance signals. However, it is not clear whether the expressions of iron uptake genes are influenced by long-distance signals or not in strategy II plants. In this study, we carried out the leaf-excision experiment to find a clue of the long-distance signals in strategy II plants. The expression of GUS transgene driven by HvIDS2 promoter of barley disappeared by the leaf-excision in tobacco roots, suggesting there are transcription factors and other functional components for activation of the long-distance signaling cascade of strategy I plants in tobacco plants. Furthermore we compared the expression of OsNAS1 and OsIRO2 in rice plants with that of iron uptake genes in non graminaceous plants after the leaf-excision. The expression pattern of OsNAS1 and OsIRO2 was similar to that of AtFRO2 and AtbHLH38, respectively. These results likely indicate the long-distance signals are involved in iron uptake in strategy II plants as well as strategy I plants.