Simultaneous Fe- and Cu-deficiency synergically accelerates the induction of several Fe-deficiency stress responses in Strategy I plants

Under Fe-deficiency, Strategy I plants develop certain Fe-deficiency stress responses in their roots, such as enhancement of ferric reducing capacity, acidification of the medium, release of flavins and development of subapical swollen root tips. Some of these Fe-deficiency stress responses are also induced by Cu-deficiency. The aim of this work was to test whether both deficiencies, when applied simultaneously, interact in the induction of enhanced ferric reducing capacity, and also of other Fe-deficiency stress responses. The experiments were carried out with soybean (Glycine max L.), pea (Pisum sativum L.), cucumber (Cucumis sativus L.) and arabidopsis (Arabidopsis thaliana L.) plants grown in nutrient solution lacking Fe, Cu or Fe and Cu simultaneously. After treatments, ferric reducing capacity and other Fe-deficiency stress responses were determined through time. At the end of the experiments, roots and young leaves from the different treatments were collected to determine their Fe content. Results suggest that both deficiencies (Fe and Cu) interact synergically in the induction of enhanced ferric reducing capacity and of other Fe-deficiency stress responses. The induction of these responses was faster when both deficiencies were applied simultaneously than when any of the deficiencies was applied alone. To explain these results, different hypotheses are suggested and discussed.