Schematic representation of nitrogen metabolism changes occurring in Fe-deficient cucumber plants. Orange arrows indicate the specific process investigate in this work, while the arrow thickness indicates an up- or down-activation of enzymatic activities. Red arrow indicates the possible recycle of protein and aa occurring under Fe deficiency in cucumber plants. Since NO3- assimilation (NR activity) decreases and GS/GOGAT cycle increases in both root and leaf, the source of ammonia might come from a recycling of aa deriving from protein degradation as suggested in ). The aa might be partially translocated to the leaf sustaining its metabolism as supported by data presented in this work (Figures 5 and 7).