Humic acid improved germination rate, seedling growth and antioxidant system of pea (Pisum sativum L. var. Alicia) grown in water polluted with CdCl2

Seeds of pea (Pisum sativum L. var. Alicia) were germinated for 5 d by soaking in distilled water or treated with cadmium and/or humic acid (HA). Interaction between humic acid and cadmium was previously discussed. However, the regulation of the humic acid / cadmium interaction during seed germination, the first crucial stage of the plant life cycle, need to be clarified. Seed germination is an important stage of the plant life, which is highly sensitive to surrounding medium changes, since the germinating seed is the first interface of material exchange between plant cycle and environment. Relationships among cadmium stress, HA-treatment, germination rate, and changes in reserve mobilization were studied. Cadmium disrupted the soaking process that was a major event of germination. Moreover, important solutes leakage due to Cd-treatment caused disorder in reserve mobilization from cotyledons to growing embryonic axes. The observed delay in germination rate and seedling growth after Cd-treatment could be explained, partially, by the disturbance in the mobilization of water and nutrients. NADH-and MDA-activities were considered as markers of oxidative stress. they were substantially increased after Cd-treatment compared with controls but decreased in presence of AH. Excessive NADH oxidase activities proved the install of oxidative stress in Cd poisoned seeds. We suggested an antagonist effect of Cd and HA on oxidative stress enzyme activities. Treatment of seeds with Cd and/or AH maintained a high level of guaiacol peroxidase activities during five days. The possible implication of GPOX against Cd toxicity and the improvement of the antioxidant system after AH treatment proved an important implication of these findings during germination.