Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2005
Publication Date: 9/5/2006
Citation: Lucena, J.J., Chaney, R.L. 2006. Response of cucumber plants to low doses of different synthetic iron chelates in hydroponics. Journal of Plant Nutrition. 30:795-809. Interpretive Summary: Iron chelates are applied for high value fruit crops grown on calcareous soils. These soil conditions inhibit iron uptake by plants. The present study was undertaken to test properties of known commercial chelating agents with regard to how they are used by plants. We used iron-stressed cucumber plants which use a combination of reduction of ferric to ferrous, and acidification of the rhizosphere to remove iron from iron-chelates. Previously most researchers had not considered the ability of the chelating agent to compete for ferrous ion and inhibit use of iron from different chelating agents. Both the rate of reduction at pH 7.5 (similar to calcareous soils), and uptake and transfer of iron from the chelate to xylem exudate of the cucumber plants to test a diverse collection of chelating agents which have been used to fertilize crops, or are being considered for commercialization. This work showed the much higher rate of reduction than uptake of iron. And certain chelating agents were much less effective iron sources for uptake by these plants. Comparison of different chelating agents indicated that some were less useful because the compound competes to well for ferrous with the root, and catalyzes reoxidation to ferric. With these results the biological basis for value of commercial iron chelates is clarified. One new product appears to offer promise to reduce the cost of useful iron chelates for farmers.
Technical Abstract: The factors that control the use of the iron provided by iron chelates in strategy I plants are not well known. In this paper we study the effectiveness of low concentrations of a series of pure Fe chelates to supply iron to cucumber plants in hydroponics. The Fe Chelate Reductase (FCR) of the roots was measured using Fe-EDTA as substrate. Despite of the differences found in SPAD and biometric indexes among the treatments, FCR and iron in xylem sap were only significantly larger for the Fe-EDDHMA treatment. Nutritional indexes followed the opposite trend than the stability of the chelates, except for Fe-EDTA that gave the poorest results. A mechanism describing the uptake process, considering the reoxydation of the Fe(II) reduced by the FCR and the formation of the Fe(II) complex is proposed.