Biochemical changes associated with cadmium and copper stress in germinating pea seeds (Pisum sativum L.)

Seeds of pea (Pisum sativum L.) were germinated for four days over two sheets of filter paper moistened with H2O (control) and 5 mM Cd(NO3)2 or CuSO4 (treated). The relationship between heavy-metal stress and breakdown of storage compounds was studied. Germination rate and growth of radicle decreased, while the water content in stressed seeds remained around the control values. Cotyledons changed their biochemical constituents: disorders in the contents of micronutrients (Fe, Mn, Zn), free amino acids and soluble sugars were found. Decline of alpha-amylase activity as well as acid phosphatase were also observed, whereas beta-amylase and alkaline phosphatase ones were not modified by heavy-metal treatments. These results suggest that the inhibition of seed germinations after exposure to cadmium or copper is not the consequence of starvation in water uptake by seed tissues, but may be due to a failure in the reserve mobilization process from cotyledons.