Detoxification of heavy metals by the interaction between mycorrhizal fungi and jasmonic acid: Modulation of the antioxidant defense system and protein profile in maize

Abstract

The effect of exogenously applied arbuscular mycorrhizal (AM) fungi (Glomus fasiciculatum) and jasmonic acid (JA) on the ability of maize plants to alleviate heavy metal stress, induced by 2 and 4mM Zn or Cr+3 ions was investigated. The results showed that both heavy metal ions induced oxidative stress response in maize plants treated or non-treated with AM fungi and /or JA. Therefore, a significant increase in the production of H2O2 and lipid peroxidation (as indicated by malondialdhyde, MDA) and a decrease in ascorbic acid (ASA) content in maize leaves was the physiological response of the metal- induced generation of O2 radicals and subsequent cell or tissue damage. Results indicated that AM fungi and JA individually or in combination reduced Zn and Cr+3 toxicity, which is closely associated with the decrease in H2O2 formation and membrane lipid peroxidation. Moreover, Zn and Cr+3 stress induced alteration in the activities of the enzymatic antioxidant defense system such as guaiacol peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX)and superoxide dismutase (SOD). AM fungi and/ or JA significantly increased activities of the antioxidant enzymes in leaves of stressed maize plants, which is considered to play an active role in the cellular defense strategy against oxidative stress and may have important ecological consequence for the adaptation of plants to heavy metal stress. On the other hand, the present results indicated that Zn and Cr+3 treatments caused a highly significant reduction in the contents of total soluble proteins and nucleic acids (DNA & RNA) compared with the corresponding control values. Despite of this, the plants treated with both AM fungi and JA had higher total protein and nucleic acid contents at all concentrations of Zn and Cr+3 ions. SDS- PAGE electrophoresis revealed that AM fungi and / or JA evokes changes in the pattern of protein profile of maize leaves in response to 4mM of both Zn and Cr+3 ions. Thus, disappearance of some bands and appearance of novel protein bands of low molecular weights in these plants could be attributed in heavy metal tolerance.

It was concluded that AM fungi and JA individually or in combination alleviated toxicity of both Zn and Cr+3 ions in maize plants mediated by the reduction in the level of H2O2 and MDA, induction in the activity of antioxidant defense system and novel proteins of low molecular weights. Finally, applying of mycorrhizal fungi or JA reduced oxidative stress induced by Zn and Cr+3 ions, but the positive response was more pronounced when AM fungi and JA were applied together.