Abstract
The aim of this study was to assess the effect of symbiotic bacteria inoculation on the response of Medicago truncatula genotypes to iron deficiency. The present work was conducted on three Medicago truncatula genotypes: A17, TN8.20, and TN1.11. Three treatments were performed: control (C), direct Fe deficiency (DD), and induced Fe deficiency by bicarbonate (ID). Plants were nitrogen-fertilized (T) or inoculated with two bacterial strains: Sinorhizobium meliloti TII7 and Sinorhizobium medicae SII4. Biometric, physiological, and biochemical parameters were analyzed. Iron deficiency had a significant lowering effect on plant biomass and chlorophyll content in all Medicago truncatula genotypes. TN1.11 showed the highest lipid peroxidation and leakage of electrolyte under iron deficiency conditions, which suggest that TN1.11 was more affected than A17 and TN8.20 by Fe starvation. Iron deficiency affected symbiotic performance indices of all Medicago truncatula genotypes inoculated with both Sinorhizobium strains, mainly nodules number and biomass as well as nitrogen-fixing capacity. Nevertheless, inoculation with Sinorhizobium strains mitigates the negative effect of Fe deficiency on plant growth and oxidative stress compared to nitrogen-fertilized plants. The highest auxin producing strain, TII7, preserves relatively high growth and root biomass and length when inoculated to TN8.20 and A17. On the other hand, both TII7 and SII4 strains improve the performance of sensitive genotype TN1.11 through reduction of the negative effect of iron deficiency on chlorophyll and plant Fe content. The bacterial inoculation improved Fe-deficient plant response to oxidative stress via the induction of the activities of antioxidant enzymes.
Highlights
In plants, iron (Fe) plays an essential role in biochemical processes and plant metabolism such as respiration, photosynthesis, hydroxylation, nitrogen assimilation, symbiotic nitrogen fixation, and regulation of protein stability and as cofactors that carry out electron transfer functions [1, 2]
Both TII7 and SII4 were determined as siderophore producers
Our results show that rhizobial inoculation of Fe-deficient plants enhanced their biomass production
Summary
Iron (Fe) plays an essential role in biochemical processes and plant metabolism such as respiration, photosynthesis, hydroxylation, nitrogen assimilation, symbiotic nitrogen fixation, and regulation of protein stability and as cofactors that carry out electron transfer functions [1, 2]. Abundance of iron-deficient calcareous soils severely affects plant growth and crop yield adversely [5, 6]. Calcareous soils cover major cultivated land of south Mediterranean lands, which decreased crop growth and yield under low Fe availability. A lot of research showed that the most obvious effect of Fe deficiency is a decrease in the amount of chlorophyll pigments [7, 8]. There is a close relationship between plant growth and photosynthesis [7, 9]. Mann [8] and Ren [9] showed that plants responded strongly to iron deficiency in physiological traits where chlorophyll content and plant biomass were reduced [10]. In calcareous soils, cultivating Fe-efficient plants is important for maintaining yields while enhancing environmental sustainability
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