Iron plaque was extracted from fresh root surfaces using dithionite-citrate-bicarbonate (DCB) solution containing 0.03 M sodium
citrate (Na3C6H5O7 2H2O), 0.125 M sodium bicarbonate (NaHCO3)
and 0.06 M sodium dithionite (Na2S2O4). The whole root system
per pot was dipped into DCB solution (40 mL) at 25 C for
60 min, and then rinsed three times with deionized water. Rinsed
water was poured into the DCB extracts and the total volume
was made up to 50 mL with deionized water. The final solution
was passed through a 0.45- lm nylon filter and refrigerated at
2 C for subsequent analysis (Liu et al., 2004).