Cadmium and copper stress affect seedling growth and enzymatic activities in germinating barley seeds

To assess cadmium (Cd) and copper (Cu) phytotoxicity, barley (Hordeum vulgare L. var. 'Manel') seeds were germinated for a period of 2 days in a solution containing CdCl2 (25, 50, and 100 µM) or CuSO4 (100, 300, and 500 µM). The growth of radicles and shoots decreased while the water content in stressed seeds remained near control values. A decline in α-amylase, acid phosphatase, and alkaline phosphatase activities was also observed in endosperms, while β-amylase activity was only slightly modified by heavy metal treatments. Furthermore, Cd and Cu increased lipid peroxidation, enhanced soluble protein and sugar content even at the lowest dose, and induced a significant accumulation of proline, essentially in radicles. A synthesis of the results reveals that the inhibition of seed germination after exposure to Cd or Cu is not a consequence of reduced water uptake by seed tissues, but may be due to a failure in reserve mobilization from the endosperm.