Genetic diversity of Acacia tortilis ssp. raddiana rhizobia in Tunisia assessed by 16S and 16S-23S rDNA genes analysis.

AIMS: In order to understand the genetic diversity of Acacia tortilis ssp. raddiana-rhizobia in Tunisia, isolates from nine geographical locations were obtained and analysed. METHODS AND RESULTS: Characterization using restriction fragment length polymorphism analysis (RFLP) of PCR-amplified 16S rRNA gene and the intergenic spacer (IGS) between the 16S and 23S rRNA genes was undertaken. Symbiotic efficiency of the strains was also estimated. Analysis of the 16S rRNA by PCR-RFLP showed that the isolates were phylogenetically related to Ensifer ssp., Rhizobium tropicii-IIA, and Rhizobium tumefaciens species. Analysis of 16S-23S spacer by PCR-RFLP showed a high diversity of these rhizobia and revealed eleven additional groups, which indicates that these strains are genetically very diverse. Full 16S rRNA gene-sequencing showed that the majority of strains form a new subdivion inside the genera Ensifer, with Ensifer meliloti being its nearest neighbour. Nodulation test performed on the plant host demonstrated differences in the infectivity among the strains. CONCLUSION: Rhizobial populations that nodulate specifically and efficiently Acacia tortilis ssp. raddiana in representative soils of Tunisia is dominated by E. meliloti-like genomospecies. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper provides the first clear characterization and symbiotic efficiency data of rhizobia strains nodulating A. tortilis in Tunisia.

Effect of cadmium on lipid composition of pepper.

Seedlings (2 weeks old) of pepper (Capsicum annum) were grown in nutrient solution with added CdCl(2) (10 or 50 microM) for 7 days. In Cd-treated plants, changes in acyl lipids and fatty acid composition were investigated. Cd particularly lowered the amount of monogalactosyldiacylglycerol (MGDG) and enhanced accumulation of phospholipids [phosphatidylcholine (PC), phosphatidylethanolamine and phosphatidylglycerol] in leaves. In contrast, content of PC and galactolipids (MGDG and digalactosyldiacylglycerol) decreased in roots. Fatty acid composition of leaves was also changed by Cd addition to external medium, but no important changes occurred in roots. Levels of leaf polyunsaturated fatty acids, especially 18:3 and 16:3, were reduced. Lipid and fatty acid composition changes in roots are discussed in relation to Cd tolerance in pepper.

Cadmium- and copper-induced changes in tomato membrane lipids.

Cadmium and copper uptake and distribution, as well as their effects on growth and lipid composition were investigated in 17-day-old tomato seedlings (Lycopersicon esculentum Mill. cv. 63/5 F1) grown in culture solution supplied with two concentrations of Cd or Cu (0, 5 and 50 microM). The accumulation of Cd and Cu increased with external metal concentrations, and was considerably higher in roots than in primary leaves. Biomass production of the growing roots and primary leaves was strongly depressed at high metal levels. Also, significant decreases in the content of lipid classes and changes of fatty acid composition were recorded in heavy metal-stressed plants in comparison with controls. Glycolipid contents were decreased more in leaves than in roots by Cd-treatment, but copper decreased both to similar extents in both organs. Likewise, both metals reduced the phospholipid and neutral lipid contents more in roots than in leaves. In almost all lipid classes the proportion of palmitic acid (16:0) increased, and that of linoleic (18:2) or linolenic (18:3) acid decreased, suggesting that heavy metal treatment induced an alteration in the fatty acid desaturation processes. Furthermore, the accumulation of palmitate (16:0) rather than stearate (18:0) indicated an alteration in the ratio of products from the fatty acid synthase. Copper was found to be the most unfavourable for plant growth and lipid metabolism. The possible mechanisms by which heavy metals, especially Cu, induce a strong lipid shift are discussed.

[Zinc phytotoxicity and induction of stress proteins in bean (Phaseolus vulgaris L.)]. / Phytotoxicité du zinc et induction de protéine(s) de stress chez le haricot (Phaseolus vulgaris L.).

Bean seedlings (Phaseolus vulgaris L., cv. fin de Bagnol) were grown for ten days in nutrient solutions at 0, 50, 100, 500 and 1000 microM ZnS0(4). The results obtained show that Zn treatment is followed by a pathological behaviour, the precocity and intensity of which are dependent on the applied dose. In addition to the depressive effects on the biomass yield and the tissue water content, a decrease in the proteins contents was also observed. Zinc toxicity seems to induce synthesis of low molecular weight proteins in Zn-treated bean stems, but not in the roots and leaves. These peptides, in stems, may protect, hypothetically, the susceptibles metabolic sites in foliar parenchyma against the zinc deleterious effects.

Effects of NaCl on Flows of N and Mineral Ions and on NO3- Reduction Rate within Whole Plants of Salt-Sensitive Bean and Salt-Tolerant Cotton.

The effects of NaCl on the transport rates of cations, NO3-, and reduced N compounds between roots and shoot and on NO3- assimilation rate were examined on plants of two species differing in their sensitivity to salinity, bean (Phaseolus vulgare L. cv Gabriella) and cotton (Gossypium hirsutum L. cv Akala). Biomass production after 20 d in response to 50 and 100 mM NaCl decreased by 48 and 59% in bean, but only 6 and 14% in cotton. The comparison of the flow patterns obtained for control and NaCl-fed plants showed that salinity induced a general decrease in all the fluxes involved in partitioning of N and the various ions. This decrease was markedly higher in bean than in cotton. Within either species, the different flows (uptake, xylem flux, phloem flux) of a given element were affected by NaCl to the same extent with minor exceptions. No specific effect of salinity on any of the components of N partitioning were discerned. The greater sensitivity of nitrate reductase activity to NaCl in bean leaves compared to cotton leaves seems to be due to a decreased compartmentalization of ions rather than to a difference in salt tolerance of the enzyme itself. Overall, our data show that alteration of mineral nutrition is not solely the reflection of a decreased growth rate, but also is a general process that impairs uptake of all the minerals even at mild NaCl salinity.