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.

Impact of cadmium stress on two maize hybrids.

Some physiological parameters and composition of the root cell walls of two maize hybrids (monocots), the sensitive Novania and the tolerant Almansa were studied after treatment with cadmium cations. After 10 days of Cd2+ treatment (1 × 10-5 M and 5 × 10-5 M), plant growth inhibition, in the sensitive hybrid in particular, as well as a certain alteration in root structure and pigment content were observed. The Cd2+ accumulation was ten times higher in the roots than in the shoots. Chemical analyses and atomic absorption spectroscopy proved that Cd2+ modified the composition of the root cell walls by a significant increase in the content of alkali-soluble polysaccharide fractions, particularly in the tolerant hybrid. An increase in the content of phenolic compounds, mainly in the tolerant hybrid, and a decrease in protein content were observed in the presence of Cd2+ in the alkali fractions. The results indicate that the changes in the cell wall polysaccharide fractions and their proportion to lignin and cellulose are obviously involved in the tolerance and/or defence against Cd2+ of the maize hybrids studied.