The response of maize protoplasts to cadmium stress mitigated by silicon.

The aim of this article was to evaluate the viability of maize protoplasts, cell wall regeneration, Cd uptake by protoplasts, and the impact of silicon under cadmium cations (Cd) stress in two maize hybrids with contrasting tolerances to Cd toxicity. The differences in protoplast viability between the sensitive (Novania) and tolerant (Almansa) hybrids were noticeable even at the beginning of culture. The percentage of living protoplasts in the presence of Cd was higher in the tolerant hybrid. In both hybrids, Si supplementation significantly increased the viability of protoplasts exposed to Cd. The percentage of protoplasts with regenerated cell walls gradually increased in both hybrids and by the end of the culture it had reached almost identical values. Differences were observed during the first four days, when a lag phase occurred in the protoplasts of the sensitive hybrid accompanied by a rapid decrease in protoplast viability in all the variants tested. The addition of Si increased the cell wall regeneration compared with the Cd variant in both hybrids. The Cd content was higher in the tolerant hybrid than in the sensitive one during the first four days and declined on the seventh day. This may be connected with the increasing intensity of cell wall formation from the fourth up to the seventh day. The addition of Si decreased the Cd uptake into protoplasts of both hybrids. Despite the higher content of Cd, the protoplasts of the tolerant hybrid showed higher viability, obviously indicating unequal mechanisms of Cd processing in studied hybrids. CAPSULE: Protoplasts of two maize hybrids were tested for their viability, regeneration, Cd-uptake and the mitigation of cadmium stress by silicon.

Maize shoot cell walls under cadmium stress.

The composition of shoot cell walls of two maize hybrids (Zea mays L.), the sensitive Novania and the tolerant Almansa, both after cadmium treatment was studied. Previous results showed a smaller effect of cadmium on shoot physiological parameters (e.g., elongation, dry mass, photosynthetic pigments content) in both hybrids compared to their roots. Changes in the composition of shoot cell walls were observed. It was ascertained that the amount of hemicelluloses in shoot cell walls decreased and the amount of lignocellulose complex increased in the sensitive hybrid; the opposite was observed in the tolerant Almansa. Dissimilarities in the cell wall structure of shoots, compared to the roots, in both hybrids were observed mainly in higher quantities of total lignin, in hemicelluloses fractions. The lignocellulose complex remained unchanged in the shoots in comparison to the roots. Nevertheless, in both hybrids, the highest Cd2+ amount was found in hemicelluloses. Such modification of the cell walls might affect the amount of binding sites resulting in lower cell wall permeability and subsequently in a lower pollutant influx into the protoplast.