The effects of increasing concentrations of soil copper on a number of leaf structural parameters in oregano plants were studied to determine the effect of copper toxicity. Copper-stressed leaves were small and chlorotic and underwent a thickening of their lamina, due principally to an increase in the number and volume of mesophyll cells. The number of stomata and glandular and non-glandular hairs increased significantly. Chloroplasts of mesophyll cells declined dramatically in number and volume. Grana and stroma thylakoids of chloroplasts did not undergo any noticeable alterations, but starch grains disappeared, plastoglobuli became larger and the double membrane limiting the chloroplast became dilated. Leaf chlorosis was determined by total chlorophyll analysis and measurement of the leaf Cu, Fe and Mg content. The effects of copper toxicity on oregano leaves comprised significant structural alterations which reflect reduced metabolic activity. Copyright 2001 Annals of Botany Company

Received: 1 December 2001 ; Returned for revision: 20 February 2001 . Accepted: 4 April 2001


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