Morpho-physiological retardations due to iron toxicity involve redox imbalance rather than photosynthetic damages in tomato

Abstract

Iron (Fe) toxicity is a major nutritional disorder that affects growth and yield in plants. Understanding the responses or damages due to Fe-toxicity may provide useful knowledge to improve tomato varieties. This study investigates the physiological and molecular responses in Fe-toxic tomato plants. The tomato plants were grown in separate hydroponic containers with two concentrations of Fe-EDTA (25 μM and 5 mM) in addition to the other nutrient elements. Fe-toxicity showed a severe reduction in growth parameters, which was accompanied by the increased electrolyte leakage and cell death in tomato. However, the SPAD score, quantum efficiency of PSII, and photosynthesis performance index did not show any changes in leaves, suggesting that damages due to Fe-toxicity are not related to the photosynthetic disturbance in tomato. The FCR (ferric chelate reductase) activity in root along with the Fe concentration in root and shoot significantly increased, being consistent with the upregulation of Fe-related genes (SlNramp1 and SlFRO1) in roots. It suggests that inefficiency to cope with elevated Fe is closely linked to Fe mobilization and uptake in roots of tomato. Consequently, this sensitive genotype was more prone to oxidative damages because of the inefficient antioxidant defense linked to antioxidant enzymes and metabolites. In conclusion, the growth retardation in Fe-toxic tomato is not related to photosynthetic inefficiency but highly associated with oxidative injuries in cells. These findings could be targeted in breeding or transgenic program to improve tomato plants sensitive to Fe toxicity.

Keywords: Fe-reductase activity; Iron toxicity; PSII; Redox imbalance; Tomato.