Analysis of cadmium translocation, partitioning and tolerance in six barley (Hordeum vulgare L.) cultivars as a function of thiol metabolism

Six barley cultivars widely differing for cadmium (Cd) tolerance, partitioning, and translocation were analyzed in relation to their thiol metabolism. Results indicated that Cd tolerance was not clearly related to the total amount of Cd absorbed by plants, resulting instead closely dependent on the capacity of the cultivars to trap the metal into the roots. Such behaviors suggested the existence of root mechanisms preserving shoots from Cd-induced oxidative damages, as indicated by the analysis of thiobarbituric acid-reactive substances \u2014diagnostic indicators of oxidative stress\u2014whose increases in the shoots were negatively related to Cd root retention and tolerance. Cd exposure differentially affected glutathione (GSH) and phytochelatin (PC) levels in the tissues of each barley cultivar. The capacity to produce PCs appeared as a specific characteristic of each barley cultivar, since it did not depend on Cd concentration in the roots and resulted negatively related to the concentration of the metal in the shoots, indicating the existence of a cultivar-specific interference of Cd on GSH biosynthesis, as confirmed by the existence of close positive linear relationships between the effect of Cd on GSH levels and PC accumulation in both roots and shoots. The six barley cultivars also differed for their capacity to load Cd ions into the xylem, which was negatively related to PC content in the roots. Taken as a whole, these data indicated that the different capacity of each cultivar to maintain GSH homeostasis under Cd stress may strongly affect PC accumulation and, thus, Cd tolerance and translocation

Comparative responses to water deficit stress and subsequent recovery in the cultivated beet Beta vulgaris and its wild relative B. macrocarpa

The effects of water deficit stress and recovery on growth, photosynthesis, physiological and biochemical parameters were investigated in the cultivated Beta vulgaris and in two Tunisian provenances (Soliman and Enfidha) of its wild relative B. macrocarpa. Seedlings were cultivated for 4 weeks under optimal or limiting water supply (respectively, 100% and 25% of field capacity, FC). After 2 weeks of treatment, a lot of stressed plants were rehydrated to 100% FC. In the Control, B. vulgaris was more productive than B. macrocarpa, whereas Enfidha provenance showed the highest biomass production (1.6- and 3-fold compared with B. vulgaris and Soliman, respectively), under water deficit stress. A partial re-establishment of growth occurred in both species upon recovery at 100% FC. The sensitivity of B. vulgaris and Soliman provenance to drought was associated with the disturbance of leaf water status and the sharp decrease in net CO2 assimilation (–66% and –82% as compared with the Control, respectively). On the contrary, the better behaviour of Enfidha provenance was related to its better photosynthetic capacity and leaf relative water content, along with a higher accumulation of amino acids (proline, glycine, and glutamine) implied in the osmotic adjustment. Leaf hexose concentration increased significantly under drought stress in both species whereas leaf sucrose concentration declined only in drought-stressed B. vulgaris and Soliman provenance. Leaf glutamate dehydrogenase activity increased under water deficit in both species despite to a higher extent in B. vulgaris. As glutamate dehydrogenase is implied in catabolism of glutamate to oxoglutarate, it might contribute to provide stressed plants with carbon skeletons. Enfidha provenance of the spontaneous species B. macrocarpa could be used in the marginal arid ecosystems in order to limit the deficit in fodder and to improve the pastoral value of these regions. In addition, this species could serve as a source of genes for genetic improvement to water deficit stress

Cross-tolerance to abiotic stresses in halophytes: Application for phytoremediation of organic pollutants

International audienceHalopytes are plants able to tolerate high salt concentrations but no clear definition was retained for them. In literature, there are more studies that showed salt-enhanced tolerance to other abiotic stresses compared to investigations that found enhanced salt tolerance by other abiotic stresses in halophytes. The phenomenon by which a plant resistance to a stress induces resistance to another is referred to as cross-tolerance. In this work, we reviewed cross-tolerance in halophytes at the physiological, biochemical, and molecular levels. A special attention was accorded to the cross-tolerance between salinity and organic pollutants that could allow halophytes a higher potential of xenobiotic phytoremediation in comparison with glycophytes

Implication of citrate, malate and histidine in the accumulation and transport of nickel in Mesembryanthemum crystallinum and Brassica juncea

Citrate, malate and histidine have been involved in many processes including metal tolerance and accumulation in plants. These molecules have been frequently reported to be the potential nickel chelators, which most likely facilitate metal transport through xylem. In this context, we assess here, the relationship between organics acids and histidine content and nickel accumulation in Mesembryanthemum crystallinum and Brassica juncea grown in hydroponic media added with 25, 50 and 100 µM NiCl2. Results showed that M. crystallinum is relatively more tolerant to Ni toxicity than B. juncea. For both species, xylem transport rate of Ni increased with increasing Ni supply. A positive correlation was established between nickel and citrate concentrations in the xylem sap. In the shoot of B. juncea, citric and malic acids concentrations were significantly higher than in the shoot of M. crystallinum. Also, the shoots and roots of B. juncea accumulated much more histidine. In contrast, a higher root citrate concentration was observed in M. crystallinum. These findings suggest a specific involvement of malic and citric acid in Ni translocation and accumulation in M. crystallinum and B. juncea. The high citrate and histidine accumulation especially at 100 µM NiCl2, in the roots of M. crystallinum might be among the important factors associated with the tolerance of this halophyte to toxic Ni levels

Why does the halophyte Mesembryanthemum crystallinum better tolerate ni toxicity than brassica juncea : Implication of antioxidant defense systems

IThe implication of enzymatic and non-enzymatic antioxidative systems in response to Ni was evaluated in the halophyte Mesembryanthemum crystallinum in comparison with the metal tolerant glycophyte species Brassica juncea. Seedlings of both species were hydroponically subjected during 21 days to 0, 25, 50, and 100 \ub5M NiCl2. Growth parameters showed that the halophyte M. crystallinum was more tolerant to Ni than B. juncea. Malondialdehyde (MDA) content increased to a higher extent in B. juncea than in M. crystallinum. Antioxidant enzymesactivities were differently affected by Ni in both species. Nickel increased shoot superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities in B. juncea, whereas these activities were reduced in M. crystallinumwhen exposed to metal stress. The root SOD, APX and guaiacol peroxidase (GPX) activities increased upon Ni treatments for both species. The content of non-enzymatic antioxidative molecules such as glutathione, non-protein thiols and proline increased in Ni-treated plants, except for GSH content in the shoot of B. juncea. Based on the oxidative balance, our findings confirm the higher tolerance of the halophyte M. crystallinum to Ni-induced oxidative stress comparatively to B. juncea. We suggest that M. crystallinum is able to overcome the produced ROS using the non-enzymatic system, while Ni-induced oxidative stress was more acute in B. juncea, leading this species to mainly use the enzymatic system to protect against reactive oxygen species

Efficient rhizobacteria promote growth and alleviate NaCl-induced stress in the plant species Sulla carnosa

Peer reviewe

Comparative Ni tolerance and accumulation potentials between Mesembryanthemum crystallinum (halophyte) and Brassica juncea : metal accumulation, nutrient status and photosynthetic activity

Saline soils often constitute sites of accumulation of industrial and urban wastes contaminated by heavy metals. Halophytes, i.e. native salt-tolerant species, could be more suitable for heavy metal phytoextraction from saline areas than glycophytes, most frequently used so far. In the framework of this approach, we assess here the Ni phytoextraction potential in the halophyte Mesembryanthemum crystallinum compared with the model species Brassica juncea. Plants were hydroponically maintained for 21 days at 0, 25, 50, and 100\u3bcM NiCl2. Nickel addition significantly restricted the growth activity of both species, and to a higher extent in M. crystallinum, which did not, however, show Ni-related toxicity symptoms on leaves. Interestingly, photosynthesis activity, chlorophyll content and photosystem II integrity assessed by chlorophyll fluorescence were less impacted in Ni-treated M. crystallinum as compared to B. juncea. The plant mineral nutrition was differently affected by NiCl2 exposure depending on the element, the species investigated and even the organ. In both species, roots were the preferential sites of Ni2+ accumulation, but the fraction translocated to shoots was higher in B. juncea than in M. crystallinum. The relatively good tolerance of M. crystallinum to Ni suggests that this halophyte species could be used in the phytoextraction of moderately polluted saline soils