APPLICATION OF CHELATOR-BUFFERED NUTRIENT SOLUTION TECHNIQUE IN STUDIES ON ZINC NUTRITION IN RICE PLANT (ORYZA-SATIVA L)

It has been difficult to impose different degrees of Zn deficiency on Poaceae species in nutrient solution because most chelators which woul d control Zn to low activities also bind Fe3+ so strongly that Poaceae species cannot obtain adequate Fe. Recently, a method has been develo ped to provide buffered Fe2+ at levels adequate for rice using Ferrozi ne (FZ), and use of other chelators to buffer the other micronutrient cations. The use of Fe2+ buffered with FZ in nutrient solutions in whi ch Zn is buffered with HEDTA or DTPA was evaluated for study of Zn def iciency in rice compared to a conventional nutrient solution technique . The results showed that growth of rice plants in FZ + HEDTA-buffered nutrient solution was similar to that in the conventional nutrient so lution. Severe zinc deficiency symptoms were observed in 28-day-old ri ce seedlings cultured with HEDTA-buffered nutrient solution at Zn2+ ac tivities < 10(-10.6) M. With increasing free Zn2+ activities, concentr ations of Zn, Fe, Cu, and Mn in shoots and roots were quite similar fo r the FZ + HEDTA-buffered nutrient solution and the conventional nutri ent solution techniques. The percentages of water soluble Zn, Fe, Cu a nd Mn in shoots with HEDTA-buffered nutrient solution were also simila r to those with the conventional solution. However, with DTPA-buffered nutrient solution, the rice seedlings suffered severe Fe deficiency; adding more FeFZ(3) corrected the Fe-chlorosis but shifted microelemen t buffering. Further, much higher total Zn concentrations are required to provide adequate Zn2+ in DTPA-buffered solutions, and the contents of Mn and Cu in shoots and roots cultured with DTPA-buffered solution s were much higher than those with the conventional or HEDTA-buffered solutions. In conclusion, DTPA-buffered nutrient solutions are not sui table but the FZ/HEDTA-buffered nutrient solution technique can be use d to evaluate genotypic differences in zinc efficiency in rice.