Effect of nitrogen supply on iron accumulation in maize kernels

Iron(Fe) nutrition of cereal grains has substantial influence on human and animal health.This trait can be determined by many physiological processes such as Fe uptake,transport in xylem,storage in vegetative organs,retranslocation via phloem to grains and deposition in grains.Much progress has been achieved in understanding of iron uptake.Nevertheless,less is known about the physiological basis for Fe nutrition in grains.Nitrogen(N) has substantial influence on iron nutrition in plants in many aspects.For example iron availability to plants is higher with ammonium compared with nitrate.Regarding to iron accumulation in grains,N supply may affect Fe concentration of grains by changing the export of Fe from vegetative organs.In the present study,after silking Fe uptake and export from different vegetative organs of maize and their potential contribution to kernel Fe accumulation was investigated under high and low N supplies.It was showed that N levels had no significant influence on Fe concentration in kernels.Under both N levels,stem(including sheathes and tassels) had the highest Fe export amount,Fe export percentage(40.4%48.2%) and the potential contribution percentage(50.9%69.8%) to kernel Fe.The middle leaves(ear-leaf and the 2 leaves above,the 2 leaves below),on the contrary,showed net increase of Fe content.Compared with high N,Fe export amount and percentage from vegetative organs was lower,while Fe uptake was higher under low N.The total Fe source,including post-silking Fe uptake and Fe export from vegetative organs,was more than the amount of Fe accumulated in kernels under both N levels,which indicated that Fe uptake and transport were not the limiting factors for kernel Fe accumulation.It is suggested that loading and metabolism of Fe in kernels may be the limiting factor for Fe accumulation.