Ecophysical and ultrastructural effects of copper in Thlaspi ochroleucum (Cruciferae)

Abstract

The toxic effects of Cu on growth, element uptake, chlorophyll content, cellular ultrastructure, and morphometry of a Zn-and Pb-tolerant ecotype of Thlaspi ochroleucum have been investigated in hydroponic cultures. Increasing Cu concentrations in nutrient solutions caused a reduction of root growth, a decrease in total chlorophyll content in the leaves, an increased uptake of Cu, and a decreased uptake of nutrient elements such as Ca, Mg, K, and Fe. Gross anatomy and intercellular spaces of leaves of plants treated with Cu did not differ significantly from the controls. However, cells contained fewer and smaller chloroplasts that lacked starch grains and contained a number of large plastoglobuli. The volume fraction of the internal membrane system was reduced, but ultrastructurally it was similar to the control. These findings, in combination with the reduced quantity of chlorophyll, indicate that the existence of a well-organized internal membrane system does not necessarily imply the presence of high amounts of chlorophyll. Other leaf cell components, such as mitochondria, microbodies, and nuclei, displayed little ultrastructural malformation. In roots, however, all cell types were so disorganized by treatment with Cu that cell organelles could hardly be identified. Our results indicate that toxic effects of Cu appear to be manifested primarily in roots and secondarily on aerial plant parts. Key words: chlorophyll content, copper, element uptake, morphometric cytology, ultrastructure, Thlaspi ochroleucum.