Inclusion of urea in a 59FeEDTA solution stimulated leaf penetration and translocation of 59Fe within wheat plants

The role of urea in the translocation of Fe-59 from (59)FeEDTA-treated leaves was studied in durum wheat (Triticum durum) grown for 2 weeks in nutrient solution and until grain maturation in soil culture. Five-cm long tips of the first leaf of young wheat seedlings or flag leaves at the early milk stage were immersed twice daily for 10s in (59)FeEDTA solutions containing increasing amounts of urea (0, 0.2, 0.4 and 0.8% w/v) over 5 days. In the experiment with young wheat seedlings, urea inclusion in the (59)FeEDTA solution increased significantly translocation of Fe-59 from the treated leaf into roots and the untreated part of shoots. When Fe-59-treated leaves were induced into senescence by keeping them in the dark, there was a strong Fe-59 translocation from these leaves. Adding urea to the Fe-59 solution did not result in an additional increase in Fe translocation from the dark-induced senescent leaves. In the experiment conducted in the greenhouse in soil culture until grain maturation, translocation of Fe-59 from the flag leaves into grains was also strongly promoted by urea, whereas Fe-59 translocation from flag leaves into the untreated shoot was low and not affected by urea. In conclusion, urea contributes to transportation of the leaf-absorbed Fe into sink organs. Probably, nitrogen compounds formed after assimilation of foliar-applied urea (such as amino acids) contributed to Fe chelation and translocation to grains in wheat.