Effect of indole-3-acetic acid on lead accumulation in maize (Zea mays L.) seedlings and the relevant antioxidant response

The effect of indole-3-acetic acid (IAA) on lead (Pb) accumulation in maize (Zea mays L. cv. TY2) seedlings, and the responses of maize to Pb, IAA or Pb + IAA stress were investigated under hydroponic conditions. Exogenous IAA significantly increased Pb accumulation in roots, but significantly decreased Pb accumulation in shoots over the culture period of 5 days. Increased Pb uptake in maize roots partly took place through calcium and potassium channels, and also depended upon membrane potential. Lipid peroxidation in terms of malondialdehyde (MDA) content was enhanced, indicating that Pb and/or IAA caused oxidative stress in maize seedlings. Under stress conditions the antioxidant defense mechanism was activated. Some antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were up-regulated compared to the control. Pb, IAA or Pb + IAA treatments resulted in a general reduction of macro- and micronutrient contents, especially of K, Ca and Mn. Compared to a single Pb or IAA treatment, treatment with a combination of Pb + IAA induced more severe oxidative stress on maize roots and shoots as inferred from the higher observed MDA and lower nutrient contents. A Fourier transform infrared (FTIR) spectroscopic study indicated that Pb reacted with the carboxylic acid group of the IAA pyrrole cycle.