Brassinosteroids and iron plaque affect arsenic and cadmium uptake by rice seedlings grown in hydroponic solution

Brassinosteroids (Brs) have drawn wide attention due to their protective role against toxicity of heavy metals in plants. To better understand the role of Br in arsenic (As) and cadmium (Cd) uptake by rice plants, a hydroponic experiment was conducted to investigate the combined effect of 24-epibrassinolide (Br24) or 28-homobrassinolide (Br28) and iron plaque (IP) on As and Cd uptake and accumulation in rice seedlings. Six-week-old seedlings were sprayed with 0.2 or 0.02 mu M Br24 or Br28 and grown in nutrient solution for 3 d, and then 20 or 60 mg Fe2+ dm(-3) (Fe20 and Fe60) was used to induce root IP formation for 3 d. These seedlings with or without Br and with or without IP were exposed to solution containing 0.5 mg dm(-3) As-III or Cd for 9 d. The results showed that rice growth decreased when Br24 were applied, but it increased when combination of Br24 and IP was applied. Fe concentrations in dithionite-citratebicarbonate (DCB) extracts were increased after 0.2 or 0.02 mu M Br24 application in the absence of IP, but decreased by Br24 in the presence of IP. In the absence of IP, As and Cd content in leaves was significantly reduced by 0.02 mu M Br24 and 0.2 mu M Br28, respectively. The As content in leaves was also reduced by the combination of 0.02 and 0.2 mu M Br28 and IP, and the Cd content in leaves was reduced by the combined effect of 0.2 mu M Br24 and IP. These results indicate that Br24 and Br28 could impede As and Cd accumulation, and the interactions between Br and IP may have a potential in restricting the transport of As and Cd into rice shoots.