Long-distance signaling of iron deficiency in plants.

In a recent issue of the Planta, we established two points regarding the long-distance signal of iron status in tobacco (Nicotiana tabacum L.). One is that the long-distance signal generated in iron deficient tissues is a major factor in positively regulating the expressions of iron uptake genes in tobacco. The expression of a ferric chelate reductase gene (NtFRO1) and an iron-regulated transporter gene (NtIRT1) in roots decreased by cutting off the leaves grown under the iron-deficient condition. Conversely, the leaf-excision did not cause upregulation of the genes under the iron-sufficient condition. These results indicated that signals sent from shoots regulate iron uptake in roots under the iron-deficient condition. The second point regarding the long-distance signals is that the strength of the long-distance signals depends on the size of plant including roots. Both genes expressed in proportion to the weight of the remaining leaves, until a certain threshold. The gene expressions were observed also in hairy roots cultured under the iron deficient condition. In this paper, we discuss the long-distance signals of iron status in plants, using a newly obtained data.