Maria da Conceição Rangel, Associate Professor at ICBAS_University of Porto and REQUIMTE-LAQV details an aspect of plant nutrition that concerns the design of efficient Fe-shuttles to prevent iron-deficiency chlorosis (IDC)
Iron (Fe) is one of the most abundant elements in Earth’s crust, and the most abundant transition metal, being an essential micronutrient for all living organisms, with the exceptions of Lactobacilli and Borrelia burgdorferi. Despite its abundance, the geological availability of Fe is compromised by the fact that the element exists in insoluble chemical forms making its uptake extremely difficult to living organisms. Bacteria and plants obtain iron from the environment by chelation, whereby the element is chemically bound to another substance making the whole complex (Fe-chelate) soluble and available. Chelation is the chemical tool used by living organisms for metal ion absorption, transport, storage and biological function and a judicious choice of a chelator allows tuning physicochemical properties of the metal ion chelate.
The absence of a proper amount of Fe puts plants health at risk since such lack has implications in several functions namely the biosynthesis of chlorophyll. Iron deficiency chlorosis (IDC) is a severe condition in which Fe-deficient plants develop yellowing of the younger trifoliate leaves, reduced leaf areas and shoot and root dry weight leading to reduced crop’s yield and serious economic losses.
The problems raised by low iron availability are reflected not only in plant´s growth but also in the Fe content of the seeds and fruits. Consequently, this problem affects animal nutrition and health since vegetables, cereals and fruits are common sources of the element. Plants represent a huge part of the human diet and in certain regions account for up to 80% of the daily Fe intake. This makes healthy plants with the appropriate concentrations of Fe an important health issue because iron-deficient diets are a significant contributor to iron deficiency anaemia, a disorder that affects large numbers of the population in both the developed and developing world.
In addition, livestock rations are also mostly comprised of plant material we produce. Thus, the cultivation of cereals, vegetables and fruits with better nutritional properties will have an enormous impact on human health. The successful cultivation of crops with the finest nutritional properties is an issue of paramount importance in agriculture and health and consequently determinant for a sustainable development.
Iron deficiency chlorosis is particularly severe in alkaline soils, which constitute approximately 30% of the world’s arable land. Consequently, farmers must rely on supplementing their crops with iron to avoid serious growth deficiencies and disorders, such as IDC. Soil or foliar application of synthetic Fe-chelates is one of the common measures to correct IDC. Fe-chelates derived from polyaminocarboxylic acids, namely Fe-EDTA and Fe-EDDHA, are the available commercial products used in an agricultural context and some drawbacks have already been reported in this respect. The limited number of distinct Fe chelates that are used as fertilizers calls for the identification of new ligands capable of producing Fe-complexes with properties that allow more efficient pathways for root uptake, root to shoot translocation and the maintenance of metal homeostasis.
The long-term objective of the project is to design better (Fe)rrying vehicles to shuttle iron into plants and to understand how these new Fe shuttles work in planta. To achieve this purpose, research is developed following three main vectors:
Design of Fe-chelates;
- Evaluation of Fe-chelate efficiency in a model plant soybean (Glycine max L.) and;
- Investigation of the mechanisms of uptake and root-to-shoot translocation of the Fe-chelates at a physiological, biochemical and molecular level.
The innovation and key idea of this proposal is the formulation of Fe-chelates based on a distinctive family of chelators that permits the design of compounds with a variety of chemical properties that can be fine-tuned according to the results obtained on the evaluation of their biological properties. Such a possibility allows not only the improving of the performance of the fertilizer but also the investigation of the mechanisms underlying their activity.
In the first study regarding the hydroponic growth of soybean (Glycine max L.), we tested a new family of Fe-chelates and found that they have great potential as new IDC correctors since plants were significantly greener and had increased biomass when compared to plants supplied with the commercial fertilizers. In particular, plants supplied with one of the compounds were able to translocate more iron from the roots to the shoots. Moreover, the feedback from the study already inspired the modification of the chelator’s structures and new ones are currently on trial.
Having identified one lead compound that shows very promising characteristics we will proceed to: (a) an understanding of which physicochemical properties are crucial; (b) the establishment of structure-activity relationships and (c) an investigation into the mechanisms of uptake and root-to-shoot translocation of the Fe-chelates at a physiological, biochemical and molecular level.
In a recent pilot study performed in artificial soil, the lead compound was compared with the commercially available fertilizer and, the compound also revealed to be advantageous in such conditions.
The PI of the project1, Maria Rangel, is a Bioinorganic Chemist whose lab focuses on designing molecules that can bind and deliver metal ions to address biomedical and environmental issues. During the past decade, there has been a particular interest in the design of iron chelators to address infection and iron overload disorders. The evolution of the field of plant nutrition seemed quite challenging within the Fe biology area. The Co-PI, Marta Vasconcelos heads the PlanTech group and is devoted to the fields of plant nutrition and plant physiology with the major goal of reducing human malnutrition.
The multidisciplinary and complementary research team is composed by 14 members working in two research units LAQV@REQUIMTE (University of Porto) and CBQF@ESB-UCP (Portuguese Catholic University).
A strong collaboration between the fields of bioinorganic chemistry and plant biology is not so often visible and has been very enriching and a big success. The two research groups had not interacted before and learned a lot from each other. Quite a few young scientists and students became very interested in this topic, and have joined the team to work as PhD students and project trainees.
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Maria da Conceição Rangel
ICBAS-University of Porto
Tel: +351 220 402 593