Ultrastructural and metabolic disorders induced by short-term cadmium exposure in Avicennia schaureriana plants and its excretion through leaf salt glands.

Environmental cadmium (Cd) sources have increased in mangrove sediments in recent decades, inducing cellular damages in plants. Avicennia schaueriana is abundant in mangrove sites and are subjected to Cd contamination. The possible effects of Cd toxicity and the structural and physiological disturbances to this constraint were studied. Can this plant express early cellular tolerance mechanisms to such metal? Seedlings of A. schaueriana were collected from sites of their natural occurrence, placed in plastic pots containing nutrient solution for sixty days, and subsequently exposed to increasing Cd concentrations for 5 days in experimental conditions. The anatomical, ultrastructural, and physiological changes induced by Cd were analyzed. Cd accumulated mainly in the root system and also in pneumatophores, stems, and leaves, and induced differential accumulation of mineral nutrients, but did not induce necrosis or changes in leaf anatomy. However, a decrease of starch grains, and an increase of electron-dense deposition material into the cortex and vascular bundle were observed. Cd induced both increases - calcium content in shoots and calcium oxalate crystals precipitation in leaf mesophyll - and it was detected in the crystals and in the secretion of salt glands. Our observations and experimental results provided evidence of Cd tolerance in A. schaueriana. As a new feature, despite the clear cell physiological disorders, this plant is able to eliminate Cd through leaf salt glands, and to immobilize it in calcium crystals, representing fast mechanisms of Cd exclusion and complexation in leaves in heavy metal coastal polluted marine ecosystems. This article is protected by copyright. All rights reserved.