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