Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/7/2006
Publication Date: 7/7/2006
Citation: Alcaniz, S., Cerdan, M., Sanchez-Sanchez, A., Jorda, J.D., Grusak, M.A. 2006. Iron uptake from FeEDDHA isomers by pea plants at different pH values. In: Proceedings of the Thirteenth International Symposium on Iron Nutrition and Interactions in Plants, July 3-7, 2006, Montpellier, France. p. 115.
Technical Abstract: Iron deficiency is a worldwide agricultural problem that decreases the yield and the quality of crops. Nowadays, the most effective fertilizer to solve this problem is based on ferric ethylenediamine-N,N'-bis(2-hydroxy)phenylacetic acid (FeEDDHA). This iron chelate is an efficient iron source for calcareous and alkaline soils, making iron available in the soil solution over a wide range of pH values. Commercial iron chelates derived from FeEDDHA yield two geometric isomers of this ferric chelate with differing stabilities: ferric ethylenediamine-N,N-bis(o-hydroxyphenylacetic) acid [Fe(o,o-EDDHA)] and ferric ethylenediamine-N-(o-hydroxyphenylacetic)-N'-(p-hydroxyphenylacetic) acid [Fe(o,p-EDDHA)], with Fe(o,o-EDDHA) being more stable than Fe(o,p-EDDHA). Because of the distinct stabilities and forms of these isomers at diverse pH values, there are potential differences between these isomers as iron providers to plants. In this work we studied the effectiveness of FeEDDHA as an iron source, by assessing the ability of pea plants (Pisum sativum; cv Sparkle) to reduce and take iron from Fe(o,o-EDDHA) or Fe(o,p-EDDHA). Experiments were conducted to measure either iron reductase activity or iron uptake, in response to differing isomers and/or pH. Firstly, plants were grown in aerated nutrient solution with 5 µM chelated Fe (Fe sufficiency) or without iron (Fe deficiency) to analyse the action of Fe concentration on the reductase activity. The reduction of Fe from Fe(o,o-EDDHA) was higher in Fe deficiency than Fe sufficiency. Next, the effect of pH was tested at Fe sufficiency by growing plants in aerated nutrient solution with 3 µM Fe(o,o-EDDHA). With this growth regime the reductase activity was lower at pH 6 than pH 8. Finally, we determined the iron uptake of pea roots from both isomers of FeEDDHA at pH 6 or pH 8 and from FeEDTA at pH 6, by using 59Fe-labeled chelates with roots of iron-stressed plants. Fe influx into roots was dramatically lower for both Fe(o,p-EDDHA) and Fe(o,o-EDDHA) isomers at pH 8 relative to pH 6, with the influx of iron being similar for Fe(o,p-EDDHA) at pH 8 and Fe(o,o-EDDHA) at pH 6. The quantity of Fe taken up from either isomer of FeEDDHA was significantly higher than for FeEDTA, with the highest Fe uptake being for Fe(o,p-EDDHA). Based on these results, the reductase activity of Pisum sativum (cv Sparkle) is higher for plants grown at low concentrations of Fe and it is lower in the Fe sufficiency situation for pH 6 than pH 8. Additionally, the iron influx at pH 6 is significantly higher for Fe(o,p-EDDHA) than from Fe(o,o-EDDHA) and FeEDTA, and the quantity of absorbed iron was significantly lower at pH 8 than pH 6. Our results suggest that Fe(o,p-EDDHA) is a better source of iron than Fe(o,o-EDDHA) for the assimilation of this nutrient by pea roots at pH 6. This work was supported in part by funds from the University of Alicante to S.A. and from the HarvestPlus Biofortification Project under Agreement Number 58-6250-4-F029 to M.A.G.