Micronutrient uptake and translocation in Mn-treated rice

The absorption and translocation of copper (Cu), zinc (Zn), and iron (Fe) were investigated in manganese (Mn)-treated rice (Oryza sativa L. cv. Safari) before and after the end of the mobilization of grain reserves. Rice plants were grown over a 15, 21, and 28-day period in nutrient solutions containing Mn concentrations varying between 0.125 and 32 mg 1(-1). It was found that root concentrations of Cu and Mn increased during all the experimental periods, but in 15-day-old-plants Zn decreased from the first Mn treatment onwards. In the shoots of 15-day-old plants, increasing Mn concentrations triggered an antagonistic effect on the contents of Fe, Cu, and Zn, but a synergistic tendency was found thereafter. During all the experimental periods Mn and Cu net uptake increased until the last treatment, but the absorption of Zn and Fe increased only 21 and 28 days after germination. Total shoot accumulation of these micronutrients displayed similar patterns from the 21-day onwards. After this experimental period the translocation rates also showed a synergistic increase for all metals, but in 15-day-old plants an antagonism was found between Mn and Zn. It was concluded that before and after the end of the mobilization of seed reserves, rice adaptation to high Mn concentrations is associated with significant changes of micronutrient accumulation in the tissues.