Linking phytohormones with growth, transport activity and metabolic responses to cadmium in tomato

This study investigated the role of phytohormones in the mediating effect of cadmium on growth and metabolism of tomato plants. Micro-Tom plants and its hormone mutants, procera (pro), diageotropica (dgt), epinastic (epi), and notabilis (not) have been used. Tomato seedlings were grown for 5 weeks under controlled hydroponics condition and then treated with CdCl₂ concentration ranging from 0 to 100 μM for 2- to 6-week. Lipid peroxidation, leaf chlorophyll, elemental (Cd, Fe, Zn, Ca, Mg) content, and antioxidant enzyme activity were determined. Cd stress considerably altered the transcriptional level of the metal transport-related genes. Cadmium inhibited the uptake of iron (Fe) and zinc (Zn), whereas it has no noticeable effect on magnesium (Mg) and calcium (Ca) content, which might have been induced by the defense against Cd toxicity. The overall results demonstrated that not and epi mutants (with altered levels of ABA and ethylene, respectively) had a Cd-sensitive phenotype while dgt mutant (with reduced sensitivity to auxin) avoided damaging effects of Cd stress. This observation is explained by the lowest Cd accumulation in dgt roots. These results provide valuable information for the relative importance of auxin, ethylene, and abscisic acid in regulating plant responses to heavy metal toxicity.