DISTRIBUTION OF CADMIUM IN LEAVES OF CADMIUM TOLERANT AND SENSITIVE ECOTYPES OF SILENE VULGARIS

It has been postulated that vacuolar compartmentation might play an im portant role in naturally selected cadmium tolerance in Silene vulgari s (Moench.) Garcke (Bladder campion). Additionally, a tendency of heav y metals to accumulate in the epidermis has been reported. Since these factors would affect the distribution of cadmium in leaves, we determ ined the distribution of cadmium in leaves of cadmium tolerant and sen sitive ecotypes of Silene vulgaris at different levels of exposure and at different time intervals. Cadmium concentrations were higher in le aves of sensitive plants than in those of cadmium tolerant ones after identical exposure to cadmium for a period of 8 days. The highest cadm ium concentrations were found in the lower epidermis of plants of both ecotypes. The amount of cadmium located at the lower epidermis was hi ghest for sensitive plants, although the stomatal density was lower in the sensitive ecotype than in the tolerant one. A possible explanatio n for this phenomenon is the weak relationship between transpiration ( water flow) and element allocation. Our results support the hypothesis that vacuolar storage of cadmium plays an important role in the mecha nism of cadmium tolerance in Silene vulgaris.