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.