Effects of iron toxicity on germination and initial growth of Carica papaya L.

Iron (Fe) is vital for plant development. Its excessive is harmful, both to forest and cultivated species. This study analyzed the effect of high Fe doses on the germination and initial growth of Carica papaya seeds, submitted to concentrations of 0.045, 4, and 8 mM in the form of ferrous sulfate and FeEDTA. Germination percentage, germination speed index, shoot and root growth, fresh and dry mass of the seeds were analyzed. For the initial growth the following variables were analyzed: leaf area, stem and root growth, fresh and dry mass, quantification of chloroplastid pigments, analysis of chlorophyll a fluorescence, element contents and the activity of the enzymes Superoxide Dismutase, Catalase and Peroxidase. Fe stress affected the percentage and speed of germination, root growth, and the accumulation of biomass of C. papaya , with FeEDTA being responsible for the most pronounced effects. Fe led to increases in chlorophyll and photosynthetic performance without changes in carotenoid levels. The 8 mM treatments impaired root growth, aerial growth, leaf area expansion, and biomass accumulation. The increase in Fe concentration led to an increment in its deposition in root tissue, with a drop in potassium levels in the 8 mM treatment. There was an increase in Peroxidase activity when submitted to FeEDTA. There was no difference in Superoxide Dismutase and Catalase expression in any treatment. These results show the sensitivity of C. papaya species to toxic levels of Fe, which caused damage to metabolism and initial growth.