FIGURE 12.
Working Model to explain the role of LODIS on the regulation of Fe acquisition genes. Once inside roots, Fe is translocated to leaves through the xylem, bound to citrate (provided by the FRD3 transporter). In shoots, some Fe (either as free ions or in chelated form) can enter the phloem through the OPT3 transporter, and moves back to roots bound to a chelating agent (forming LODIS). In roots, LODIS could negatively affect ethylene synthesis and signaling, and GSNOR expression and/or activity, which can lead to enhanced GSNO. Besides LODIS, which would act as a repressor of Fe responses, some other shoot signals, like sucrose and auxin, would act as activators of Fe responses through NO (Lin et al., 2016). The possible relationship of ethylene, NO, GSH, GSNOR, and GSNO is depicted in more detail in Figure 13. In green are components whose expression, activity and/or content is known to increase under Fe deficiency while in red are components whose expression, activity, and/or content is known to increase under Fe sufficiency. chel, chelating agent; GSH, glutathione; GSNO, S-nitrosogluthatione; GSNOR, GSNOR reductase; ET, ethylene; ETresp, ethylene response; Met, methionine (→: promotion; : inhibition).