Biochemical and hormonal changes associated with root growth restriction under cadmium stress during maize (Zea mays L.) pre-emergence

Cadmium (Cd) pollution of agricultural soils is a growing global concern. Plant growth restriction is the main visible symptom of Cd toxicity, and this metal may be particularly harmful to the preformed, seminal root during the pre-emergence stage. In the present study, we focused on Cd phytotoxicity in seminal root growth, nutrient composition, redox status, and hormone homeostasis during the pre-emergence stage of maize (Zea mays L) plants, distinguishing between the root apex and the remaining root tissue. After 72 h of metal exposure (50 and 100 µM CdCl2), root length and biomass, as well as Ca, Fe, Mg, and Mn contents, were diminished. A redox imbalance was evidenced by changes in peroxidase activities and the ascorbate–dehydroascorbate ratio decreased in both root parts. There were fewer carbonylated proteins in both root fractions after exposure to 50 µM Cd, compared to 100 µM Cd, which was related to increased 20S proteasome activities. Cd incremented ABA, IAA, and SA contents, but drastically reduced the biologically active gibberellin GA4 and the conjugate jasmonoyl-isoleucine (JA-Ile). We demonstrated that the whole root tissue is involved in the maize response to Cd stress, which entails redox and hormonal rearrangements, probably directed to widen the plant defense lines at the expense of root growth.