Comparative morphological and histological study on zinc- and cadmium-treated durum wheat plants with similar growth inhibition.

摘要

A comparative study of the effects of excess Zn2+ and high Cd2+ concentrations on some morphological and histological characteristics of durum wheat plants was conducted in hydroponic experiments. Treatment with the tested heavy metals was applied when plants were 8-day-old and carried on for the next 10 days. Cd2+ and Zn2+ were added to the nutrient solution at concentrations 50 and 600 micro M, respectively. These concentrations were chosen as a result of a preliminary study, where they have been found to produce similar relative growth rate (RGR) inhibition of about 50%. The results revealed that Zn2+ and Cd2+ toxic effects on wheat plants were clearly distinguished at both morphological and histological levels. Cd2+ inflicted more substantial changes in leaf structure, significantly increasing the number of the epidermal cells and stomata density on mm2, as well as reducing the mesophyll thickness. Wheat plants' response to all these xeromorphic changes in leaf structure could be presumed to be the result of cadmium negative impact on plant water relations. On the other hand, Zn2+ reduced rather insignificantly the number of the epidermal cells and stomata frequency on mm2 on both leaf surfaces, and it also reduced the mesophyll thickness by only 12%. Both metals reduced significantly the size of the root cortex. Neither Cd2+ nor Zn2+ applied in such concentrations caused abnormalities in leaf and root cells.