Morphogenetic, ultrastructural and physiological damages suffered by submerged leaves of Elodea canadensis exposed to cadmium

Although bodies of water are a major vehicle for cadmium contamination, works dealing with submerged plants directly exposed to it are still very scarce. The aim of this research was to study damaging effects of prolonged cadmium exposure on young and mature submerged leaves of Elodea canadensis treated for 1 month with 100 muM Cd added to the growth water medium. The Cd-exposed plants, compared to the controls, showed shorter and poorly pigmented shoots with thinner stems and less expanded leaves. The leaves accumulated high quantities of cadmium, most of which, about 95 and 90% in young and mature leaves, respectively, remained outside the cells, bound to the anionic cell walls. In young differentiating leaves, Cd interfered with the morphogenetic pattern, by inhibiting cell division and affecting cell enlargement. Cd hindered the division and the expansion of chloroplasts, also impairing organelle shape and thylakoid system arrangement. Cadmium, furthermore, greatly disturbed the cell wall organization, causing the demolition of the transfer cell-like frame. In differentiated leaves, Cd hastened the appearance of senescence symptoms in chloroplasts and worsened the cell wall alterations. Both young and mature leaves showed a decreased photosynthetic activity, not only ascribable to lowered chlorophyll contents. (C) 2004 Elsevier Ireland Ltd. All rights reserved.