Effects of copper toxicity on leaves of oregano (Origanum vulgare subsp hirtum)

The effects of increasing concentrations of soil copper on a number of leaf structural parameters in oregano plants were studied to determine the effe ct of copper toxicity. Copper-stressed leaves were small and chlorotic and underwent a thickening of their lamina, due principally to an increase in t he number and volume of mesophyll cells. The number of stomata and glandula r and non-glandular hairs increased significantly. Chloroplasts of mesophyl l cells declined dramatically in number and volume. Grana and stroma thylak oids of chloroplasts did not undergo any noticeable alterations, but starch grains disappeared, plastoglobuli became larger and the double membrane li miting the chloroplast became dilated. Leaf chlorosis was determined by tot al chlorophyll analysis and measurement of the leaf Cu, Fe and Mg content. The effects of copper toxicity on oregano leaves comprised significant stru ctural alterations which reflect reduced metabolic activity. (C) 2001 Annal s of Botany Company.