Leaf ontogeny of Schinus molle L. plants under cadmium contamination: the meristematic origin of leaf structural changes

Previous works show the development of thicker leaves on tolerant plants growing under cadmium (Cd2+) contamination. The aim of this study was to evaluate the Cd2+ effects on the leaf meristems of the tolerant species Schinus molle. Plants were grown in nutrient solution containing 0, 10, and 50 mu M of Cd2+. Anatomical analysis was performed on leaf primordia sampled at regular time intervals. Under the lowest Cd2+ level (10 mu M), increased ground meristem thickness, diameter of the cells, cell elongation rate, and leaf dry mass were found. However, 50 mu M of Cd2+ reduced all these variables. In addition, the ground meristem cells became larger when exposed to any Cd2+ level. The epidermis, palisade parenchyma, and vascular tissues developed earlier in Cd2+-exposed leaves. The modifications found on the ground meristem may be related to the development of thicker leaves on S. molle plants exposed to low Cd2+ levels. Furthermore, older leaves showed higher Cd2+ content when compared to the younger ones, preventing the Cd2+ toxicity to these leaves. Thus, low Cd2+ concentrations change the ground meristem structure and function reflecting on the development of thicker and enhanced leaves.