Evaluation of pesticide residues in fruits and vegetables from Algeria.

A total of 160 samples of 13 types of fresh fruits and vegetables from domestic production and import were analysed to detect the presence of pesticide residues. Analysis was performed by multi-residual extraction followed by gas chromatography-mass spectrometry. In 42.5% of the tested samples, no residues were found and 12.5% of samples contained pesticide residues above maximum residue limits. Risk assessment for long-term exposure was done for all pesticides detected in this study. Except chlorpyrifos and lambda-cyhalothrin, exposure to pesticides from vegetables and fruits was below 1% of the acceptable daily intake. Short-term exposure assessment revealed that in seven pesticide/commodity combinations, including three pesticides (chlorpyrifos, deltamethrin and lambda-cyhalothrin), the acute reference dose had been exceeded.

Localization of phytase transcripts in germinating seeds of the common bean (Phaseolus vulgaris L.).

MAIN CONCLUSION: The work provides the first-time evidence of tissue-specific expression of a phytase gene in the germinating seeds of Phaseolus vulgaris. Phytase enzyme plays a major role in germinating seeds. It is also active during N2 fixation within nodules of legumes. The effect of phosphorus (P) deficiency on phytase gene expression and localization in N2-fixing root nodules has been recently studied in hydroaeroponic culture of Phaseolus vulgaris. In this study, phytase gene transcripts within the germinating seed tissues of the P-inefficient P. vulgaris recombinant inbred line RIL147 were in situ localized with a similar RT-PCR recipe as that used for nodules. Our results show that the phytase gene expression was mainly localized in the outer layers, vascular cells and parenchyma of germinating seeds whereas it was localized in the inner and middle cortex of nodules. Image analysis quantified higher fluorescence intensity of the phytase transcript signal in the seed embryo than in radicles, cotyledons or the nodule cortex. Furthermore, the phytase activity was 22-fold higher in cotyledons (43 nmol min(-1) g(-1) dry weight) than in nodules (2 nmol min(-1) g(-1) dry weight). The K m and V m values of phytase activity in cotyledons were also significantly higher than in nodules. Interestingly, the amplified sequence of cDNA phytase exhibited highest homology with the Glycine max purple acid phosphatase (NM_001289274) 90 % for germinating seed as compared to nodule phytase cDNA displaying 94 % homology with the Glycine max phytase (GQ422774.1). It is concluded that phytase enzymes are likely to vary from seeds to nodules and that phytase enzymes play key roles in the use of organic P or N2 fixation, as it is well known for germination.

A phytase gene is overexpressed in root nodules cortex of Phaseolus vulgaris-rhizobia symbiosis under phosphorus deficiency.

Phosphorus is an essential nutrient for rhizobial symbioses to convert N2 into NH4 usable for N nutrition in legumes and N cycle in ecosystems. This N2 fixation process occurs in nodules with a high energy cost. Phytate is the major storage form of P and accounts for more than 50 % of the total P in seeds of cereals and legumes. The phytases, a group of enzymes widely distributed in plant and microorganisms, are able to hydrolyze a variety of inositol phosphates. Recently, phytase activity was discovered in nodules. However, the gene expression localization and its role in N2-fixing nodules are still unknown. In this work, two recombinant inbred lines (RILs) of common bean (Phaseolus vulgaris L.), selected as contrasting for N2 fixation under P deficiency, namely RILs 115 (P-efficient) and 147 (P-inefficient) were inoculated with Rhizobium tropici CIAT 899, and grown under hydroaeroponic conditions with sufficient versus deficient P supply. With in situ RT-PCR methodology, we found that phytase transcripts were particularly abundant in the nodule cortex and infected zone of both RILs. Under P deficiency, phytase transcripts were significantly more abundant for RIL115 than for RIL147, and more in the outer cortex than in the infected zone. Additionally, the high expression of phytase among nodule tissues for the P-deficient RIL115 was associated with an increase in phytase (33 %) and phosphatase (49 %) activities and efficiency in use of the rhizobial symbiosis (34 %). It is argued that phytase activity in nodules would contribute to the adaptation of the rhizobia-legume symbiosis to low-P environments.

Is genotypic variation of H⁺ efflux under P deficiency linked with nodulated-root respiration of N2 fixing common-bean (Phaseolus vulgaris L.)?

To examine genotypic variation of common bean in growth, phosphorus uptake, nodulated-root proton release, and nodule gas permeability, seven common bean recombinant inbred lines (RIL) from the cross of BAT477×DOR364 were inoculated by Rhizobium tropici CIAT 899 and grown in hydroaeroponic culture under glasshouse conditions. A positive correlation was observed between shoot and nodule biomass for most of the studied RILs. Under P deficiency, the tolerant common bean RILs acidified more of their rhizosphere than the sensitive ones. The proton release of the RILs 147, 124, 104, 75 and RIL34 was positively correlated with nodule O2 permeability. We conclude that nodulated common bean plants release a substantial amount of H⁺ into the rhizosphere that is linked to the symbiotic N2 fixation. It depends upon the nodule permeability to O2 diffusion, and varies with genotype.