Effect of phosphorus deficiency induced in calcareous soil on plant growth, phosphorus use efficiency and acid phosphatase activity of Medicago truncatula.

Calcareous soils, characterized by a higher pH, are frequent in the North West of Tunisia. Large concentrations of calcium carbonate in calcareous soils result in accumulation of high levels of bicarbonate ions, which complex with phosphate, resulting in phosphorus deficiency (induced P deficiency) for plants. The impact of calcareous soil on plant growth, photosynthetic activity and acid phosphatase activity was explored in two lines of Medicago truncatula: TN6.18 and Jemalong. Calcareous soil significantly restricted shoot growth only in Jemalong (-45 % of the control). When grown on calcareous soil, root length was stimulated, this effect being more pronounced in TN6.18. Under calcareous soil, net CO2 assimilation declined more in Jemalong (-40 % of the control) than in TN6.18 (-20 % of the control). CO2 accumulation was increased in Jemalong (+35% of the control) plants grown in calcareous soil. The acid phosphatase activity was higher in plants cultivated under calcareous soil. This increased phosphatase activity was more pronounced in TN6.18, which showed higher accumulation of Pi in shoots and roots than Jemalolng.  In the light of these results, the present study proposes acid phosphatase as a useful candidate for improving Pi acquisition and utilization under calcareous soil

Effect of iron deficiency on the localization of phosphoenolpyruvate carboxylase in common bean nodules

Phosphoenolpyruvate carboxylase (PEPC) plays an important role in nodules, when there is an increase in the demand for energy. This enzyme provides carbon skeletons to sustain amino acid synthesis and malate to support energy required to fix nitrogen. Since PEPC is important for nodules, and there is lack of information about the effect of some nutrient deficiency in the expression and localization of this enzyme in legume nodules, this work focused on the localization of PEPC in nodules under iron deficiency of two common bean cultivars: Flamingo tolerant and Coco blanc sensitive to iron (Fe) deficiency. The results of immunolocalization using polyclonal antibody showed that this enzyme was detected in all regions of nodule sections; but the signal intensity was increased in Fe-deficient nodules as compared to Fe-sufficient ones in the tolerant cultivar, whereas the intensity was less pronounced in nodules of Fe-deficient plants than in those of Fe-sufficient plants for the sensitive cultivar Coco blanc. This work showed that the symbiotic tolerance of Flamingo to iron deficiency was linked to the increase of PEPC enzymes expression. However, the activity of these enzymes supported the energy required in bacteroids to maintain the nitrogenase activity.Keywords: Common bean, immunolocalization, iron deficiency, nodules, phosphoenol pyruvate carboxylas

Eco-physiological responses and symbiotic nitrogen fixation capacity of salt-exposed Hedysarum carnosum plants

Nitrogen nutrition of Hedysarum carnosum, a pastoral legume common in Tunisian central and southern rangelands, largely depends on atmospheric nitrogen fixation. Yet, this process is greatly affected by environmental factors such as salinity. This study aimed to characterize the tolerance limits and the physiological responses of H. carnosum to salinity under symbiotic nitrogen fixation. Salt treatment was imposed by adding NaCl at different concentrations (0, 50, 100 and 200 mM) to the nutrient solution. Na+ content generally increased in the plant organs with increasing salinity in the culture medium. Especially, an excess accumulation of this cation was observed in leaves. Despite the fact that Na+ accumulation decreased plant growth, both nodulation and symbiotic nitrogen fixation capacity of H. carnosum appeared to be relatively salt-tolerant, owing to the plant capacity to maintain tissue hydration, control Na+ accumulation in shoots, and to conserve nodule efficiency to fix N2. Taken together, our findings indicate that H. carnosum is a glycophyte that can tolerate moderate salinity (100 mM), suggesting its possible utilization (i) in the improvement of soil fertility and (ii) in saline pastures, where the survival of other fodder species is critical.Key words: Hedysarum carnosum, nodulation, salinity, symbiotic nitrogen fixation

Effect of P on nodule formation and N fixation in bean

The present study compares the demands for P of the initial nodule formation, and of the later growth and functioning of the nodulated root system in two inoculated lines of common bean (Coco blanc and BAT477). After germination and inoculation, seedlings were divided into two lots. One lot was grown under constant P supply, either 15 (low) or 250 (high) µM P, corresponding to provision of 120 and 2000 µmol P, respectively. In the second, seedlings were cultivated on the same medium supplied with 15 µM P for 24 days after germination, and then with 60 or 250 µM (total provision of P: respectively, 390 and 1530 µmol). Nodule number and biomass were significantly diminished by the low P (120 µmol) treatment, as compared with the other treatments. However, the intrinsic characteristics of the nodules (individual biomass and size, P concentration and efficiency of N fixation) did not depend on P availability. Although the bean line BAT477 was distinguished from the Coco blanc line through higher nodule number, size, biomass, and nitrogen fixation, both lines displayed analogous responses to P availability

Effect of phosphorus deficiency induced in calcareous soil on plant growth, phosphorus use efficiency and acid phosphatase activity of Medicago truncatula.

Calcareous soils, characterized by a higher pH, are frequent in the North West of Tunisia. Large concentrations of calcium carbonate in calcareous soils result in accumulation of high levels of bicarbonate ions, which complex with phosphate, resulting in phosphorus deficiency (induced P deficiency) for plants. The impact of calcareous soil on plant growth, photosynthetic activity and acid phosphatase activity was explored in two lines of Medicago truncatula: TN6.18 and Jemalong. Calcareous soil significantly restricted shoot growth only in Jemalong (-45 % of the control). When grown on calcareous soil, root length was stimulated, this effect being more pronounced in TN6.18. Under calcareous soil, net CO2 assimilation declined more in Jemalong (-40 % of the control) than in TN6.18 (-20 % of the control). CO2 accumulation was increased in Jemalong (+35% of the control) plants grown in calcareous soil. The acid phosphatase activity was higher in plants cultivated under calcareous soil. This increased phosphatase activity was more pronounced in TN6.18, which showed higher accumulation of Pi in shoots and roots than Jemalolng.  In the light of these results, the present study proposes acid phosphatase as a useful candidate for improving Pi acquisition and utilization under calcareous soil

Genetic variability of morpho-physiological response to phosphorus deficiency in Tunisian populations of Brachypodium hybridum

Brachypodium hybridum (Poaceae) is widely distributed in the dry environments in Mediterranean basin, due to its high tolerance to drought. Investigating the natural variation of B. hybridum in response to environmental stresses is crucial for unraveling the genetic network of its stress tolerance. 79 B. hybridum lines from eight Tunisian populations were screened for their performance to low P availability using morpho-physiological parameters. ANOVA showed that treatment and population*treatment factors were the most contributors in the explained variance for the majority of parameters. A considerable population differentiation was detected in control and under P level (Qst = 0.77 vs Qst = 0.62). This suggests that B. hybridum exhibit an adaptive differential response to P deficiency related environmental conditions. Results revealed that Raouad and Sejnen lines were the most tolerant to P deficiency followed by Haouaria and Enfidha lines. The remaining populations were classified as sensitive. This pattern suggests that coastal populations were more tolerant to P deficiency than the inland ones. A slightly higher heritability was evidenced under low P level for most of traits, indicating that the direct selection under P deficiency is more reliable than an indirect one under optimal P supply.SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Nodule acid phosphatase and phytase activity of common bean (<em>Phaseolus vulgaris</em> L.) under phosphorus deficiency

National audiencePhosphorus (P) is one of the least available major nutrients to the plants in many cropping environments. P deficiency is more critical in highly weathered soils of tropics and subtropics, as well as calcareous/alkaline soils of Mediterranean basin. The production of acid phosphatase and phytase is a potential way for plants to enhance P availability, as a large proportion of soil P (up to 80%) occurs in organic forms. The effect of phosphorus availability on nodule acid phosphatase and phytase activity was studied in 2 lines of common bean (BAT 477 and Coco blanc) under symbiotic nitrogen fixation. Acid phosphatase activities were increased by P deficiency (15 µmol P) in 2 lines, this increase was more pronounced in BAT 477 than in Coco. Under P deficiency, phytase activity was higher in BAT 477 than in Coco, despite this parameter representing only 5 % of that of acid phosphatases, in the 2 lines studied, independent of the P regime. These findings suggest that phytases may be a group of enzymes that constitute acid phosphatases. Regardless of P supply in the culture medium, the content of total P was higher in nodules than in shoots for 2 lines, BAT showed the higher values. P deficiency affected this parameter in nodules, this effect was more pronounced in Coco than in BAT 477 respectively (-30%) and (-20%). Under 15 µmol P, the nodule acid phosphatase activity and the content of total P in nodule were positively correlated. These results suggest that acid phosphatases are involved in hydrolysis of organic phosphorus resulting in elevation of the (Pi) phosphorus pool

How to visualisation and localisation of acid phosphatase transcripts in common bean nodules (Phaseolus vulgaris) by in situ RT-PCR

National audienceThe symbiotic nitrogen fixation process requires phosphorus. In order to test whether acid phosphatase is involved in the phosphorus use efficiency for N2 fixation an in situ RT-PCR technology was applied to common bean nodules. The recombinant line 115 of Phaseolus vulgaris, obtained from a cross between BAT477 and DOR364, was inoculated with Rhizobium tropici CIAT 899 and grown in hydroponic cultures for 5 weeks under P deficiency. The in situ RT-PCR was carried out with 50 µm nodule sections using specific primers to amplify a 250 bp sequence in the acid phosphatase mRNA. The amplified gene product was visualized with fluorescence microscopy using the ELF-97 kit which allowed detection of the alkaline phosphatase conjugated anti-digoxigenin Fab fragments. The signal corresponding to acid phosphatase could clearly be observed except in samples without RT (control). Transcripts were distributed specifically in: i) non infected cells of the infected zone; ii) the vascular trace localised in the cortex surrounding the infected zone; iii) the inner cortex (i.e. cell-layers localised between the vascular trace and the infected zone); iv) the external cortex (i.e. layers beyond the endodermis). By contrast, no signal was detected in the mid-cortex and the infected cells. It is concluded that the in situ RT-PCR methodology can be applied to localise plant transcripts in nodules. The expression of acid phosphatase in the inner cortex suggests that this enzyme may be involved in the osmoregulation of nodule permeability to O2 and consequently in the adaptation of the legume- rhizobia symbiosis to low P suppl

Visualisation and localisation of acid phosphatase transcripts in common bean (<em>Phaseolus vulgaris</em>) nodules by in situ RT-PCR

National audienceThe symbiotic nitrogen fixation process requires much phosphorus. In order to test whether acid phosphatase is involved in the phosphorus use efficiency for N2 fixation an in situ RT-PCR approach was applied to common bean nodules. The recombinant line 115 of Phaseolus vulgaris, obtained from a cross between BAT477 and DOR364, was inoculated with Rhizobium tropici CIAT 899 and grown in hydroponic cultures for 5 weeks under P deficiency. The in situ RT-PCR was carried out with 50 µm nodule sections using specific primers to amplify a 250 bp sequence in the acid phosphatase mRNA. The amplified gene product was visualized with fluorescence microscopy using the ELF-97 kit detection of the alkaline phosphatase conjugated anti-digoxigenin Fab fragments. The signal corresponding to acid phosphatase could clearly be observed except in samples without RT (control). Transcripts were distributed specifically in: (i) non infected cells of the infected zone; (ii) the vascular trace localised in the cortex surrounding the infected zone; (iii) the inner cortex (i.e. cell-layers localised between the vascular trace and the infected zone); (iv) the external cortex (i.e. layers beyond the endodermis). By contrast, no signal was detected in the mid-cortex and the infected cells. It is concluded that the in situ RT-PCR methodology can be applied to localise plant transcripts in nodules. The expression of acid phosphatase in the inner cortex suggests that this enzyme may be involved in the osmoregulation of nodule permeability to O2 and consequently in the adaptation of the legume-rhizobia symbiosis to low P supply