Relationship between a different Cd bioavailability and the root architectural response of maize seedlings

Experimental rhyzoboxes were set up to study cadmium soil-plant interactions, and maize seedlings were used as the plant model. Zeolite and Pumice were the solid substrates, both are natural minerals with varying reactivity towards metal. The bioavailability of cadmium (Cd) in these microcosms was evaluated because it is a key factor controlling metal effects on plants. Since metal uptake by plants occurs mainly via the roots, the morphological root parameters in maize seedlings and their subsequent Cd-induced modifications were investigated. The results evidenced that cadmium treatments modify root architectural traits by a specific effect, in fact the individual components of the root apparatus show a different sensitivity to metal. In particular, nodal roots were significantly affected by cadmium. They represent younger structures than seminal or radicle roots and could have an increased demand for respiratory energy and ion uptake. The negative Cd effect on photosynthesis has been widely demonstrated; this leads to a reduced supply of carbon skeleton to roots, inhibiting the respiration rate and could also affect the nodal root growth. Maize is considered an interesting species for phytoremediation due to its considerable ability to accumulate Cd in the roots. Thus an extended knowledge of Cd-induced responses on morphological parameters in maize roots might allow us to identify root system adaptive traits for improving plant performances in phytoextraction of heavy metals from polluted soils.