Physiological and biochemical aspects of cadmium toxicity and protective mechanisms induced in Phragmites australis and Typha latifolia

The capability of common reed and cattail (Phragmites australis (Cav.) Trin. ex Steud. and Typha latifolia L.) to accumulate and translocate Cd2+ from roots to shoots and their defense mechanisms induced by Cd2+ at the levels of thiol metabolism and antioxidant enzyme activity were studied. Experiments were carried out using young, small sized plants grown hydroponically and originating either from regenerating tissue culture (reed) or aseptically germinated seeds (cattail). Cadmium treatment was applied as a concentration series between 0.1 and 100 mumol/L for 40 and 100 days for reed and cattail, respectively. For assays and analysis, plant samples were taken in 2-4 week intervals. Most of the Cd2+, taken up was retained in roots in both species, however, Typha accumulated more cadmium in the shoot compared to Phragmites. In Typha, increasing accumulation of cadmium was in positive correlation with the increase of free thiol content while in Phragmites increased glutathione reductase, catalase and peroxidase activities were found. It is shown for the first time that under Cd2+ stress different defense strategies operate in Typha and Phragmites. In Typha, this strategy relies more on thiol induction and metal binding leading to heavy metal avoidance, while in Phragmites it is based on increased antioxidant enzyme activities and thus scavenging of active oxygen species.