Abstract
BackgroundNitrogen is a principal limiting nutrient in plant growth and development. Among factors that may limit NO3- assimilation, Fe potentially plays a crucial role being a metal cofactor of enzymes of the reductive assimilatory pathway. Very few information is available about the changes of nitrogen metabolism occurring under Fe deficiency in Strategy I plants. The aim of this work was to study how cucumber (Cucumis sativus L.) plants modify their nitrogen metabolism when grown under iron deficiency.ResultsThe activity of enzymes involved in the reductive assimilation of nitrate and the reactions that produce the substrates for the ammonium assimilation both at root and at leaf levels in Fe-deficient cucumber plants were investigated. Under Fe deficiency, only nitrate reductase (EC 1.7.1.1) activity decreased both at the root and leaf level, whilst for glutamine synthetase (EC 6.3.1.2) and glutamate synthase (EC 1.4.1.14) an increase was found. Accordingly, the transcript analysis for these enzymes showed the same behaviour except for root nitrate reductase which increased. Furthermore, it was found that amino acid concentration greatly decreased in Fe-deficient roots, whilst it increased in the corresponding leaves. Moreover, amino acids increased in the xylem sap of Fe-deficient plants.ConclusionsThe data obtained in this work provided new insights on the responses of plants to Fe deficiency, suggesting that this nutritional disorder differentially affected N metabolism in root and in leaf. Indeed under Fe deficiency, roots respond more efficiently, sustaining the whole plant by furnishing metabolites (i.e. aa, organic acids) to the leaves.
Highlights
Nitrogen is a principal limiting nutrient in plant growth and development
In this work the change in the N metabolism in response to Fe deficiency has been studied at root and leaf levels
In order to guarantee that Fe-deficient plants developed clear responses in agreement with Fedeficient condition, a preliminary time course experiment on the expression of the Strategy I genes was performed at the root level (Figure 1C)
Summary
Nitrogen is a principal limiting nutrient in plant growth and development. Among factors that may limit NO3- assimilation, Fe potentially plays a crucial role being a metal cofactor of enzymes of the reductive assimilatory pathway. Very few information is available about the changes of nitrogen metabolism occurring under Fe deficiency in Strategy I plants. Nitrogen is often a limiting factor for plant growth and development. Among the factors which may limit NO3- assimilation, iron (Fe) plays a crucial role, being a metal cofactor of enzymes of the reductive assimilatory pathway [nitrate reductase (NR), nitrite reductase (NiR) and glutamate synthase (GOGAT), all requiring Fe as Fe-heme group or Fe-S cluster] [1]. Strategy I plants (dicotyledonous and non-graminaceous monocots) are able to respond to a shortage of Fe in the soil by increasing: (i) the Fe reduction capacity of root tissues [Fe3+-chelate reductase (EC 1.16.1.7] (FC-R), (ii) the acidification of the rhizosphere to increase Fe solubility [P-type H+-ATPase (EC 3.6.3.6)] and (iii) uptake activity in rhizodermal root cells
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