Abstract
Iron (Fe) is an essential element for plant growth and development. The cultivation of leguminous plants has generated strong interest because of their growth even on poor soils. Calcareous and saline soils with poor mineral availability are wide-spread in Tunisia. In an attempt to select better forage crops adapted to Tunisian soils, we characterized Fe deficiency responses of three different isolates of Hedysarum carnosum, an endemic Tunisian extremophile species growing in native stands in salt and calcareous soil conditions. H. carnosum is a non-model crop. The three isolates, named according to their habitats Karkar, Thelja, and Douiret, differed in the expression of Fe deficiency symptoms like morphology, leaf chlorosis with compromised leaf chlorophyll content and photosynthetic capacity and leaf metal contents. Across these parameters Thelja was found to be tolerant, while Karkar and Douiret were susceptible to Fe deficiency stress. The three physiological and molecular indicators of the iron deficiency response in roots, Fe reductase activity, growth medium acidification and induction of the IRON-REGULATED TRANSPORTER1 homolog, indicated that all lines responded to -Fe, however, varied in the strength of the different responses. We conclude that the individual lines have distinct adaptation capacities to react to iron deficiency, presumably involving mechanisms of whole-plant iron homeostasis and internal metal distribution. The Fe deficiency tolerance of Thelja might be linked with adaptation to its natural habitat on calcareous soil.
Highlights
Iron (Fe) is an essential micronutrient with numerous cellular functions, e.g., in photosynthesis, respiration, DNA synthesis, and N2 fixation
We were interested in obtaining an ecotype with high tolerance to prolonged Fe deficiency growth conditions, a trait expected to be beneficial upon growth on calcareous soil
Since we found no differences in the amino acid sequences of IRT1 between the three H. carnosum lines, we compared the sequence to ZIP sequences from Arabidopsis and other legumes
Summary
Iron (Fe) is an essential micronutrient with numerous cellular functions, e.g., in photosynthesis, respiration, DNA synthesis, and N2 fixation. Plants are frequently challenged by Fe deficiency, especially on alkaline and calcareous soils due to poor Fe solubility under these conditions. In Tunisia, the exploration of such kinds of natural habitats and saline environments revealed that they are colonized by a native leguminous vegetation which might have specific adaptations to both, salinity and nutrient deficiencies, especially Fe (Ben Abdallah et al, 2017). Leguminous plants take up reduced Fe using mainly the so-called Strategy. I. The main feature of Strategy I plants, e.g., in Arabidopsis thaliana and leguminous plants, is that they acidify the soil via proton extrusion through an ATPase, reduce ferric to ferrous Fe by a ferric chelate reductase and take up the divalent Fe via divalent metal IRON-REGULATED TRANSPORTER1 (Brumbarova et al, 2015), being a member of the ancient ZIP ( = ZRT/IRT1) protein family (Eng et al, 1998). IRT1 homologs were found Fe-regulated in roots of multiple legumes like Pisum sativum (Cohen et al, 2004), Medicago truncatula (Lopez-Millan et al, 2004), Arachis hypogaea (Ding et al, 2010), Glycine max (Brear et al, 2013), and Vigna radiata (Muneer et al, 2014)
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