Eduardo Gomez

Effect of mixed cadmium, copper, nickel and zinc at different pHs upon alfalfa growth and heavy metal uptake

Alfalfa plants were grown in soil-pots contaminated with a mixture of Cd(II), Cu(II), Ni(II), and Zn(II), (at 50 mg/kg each) at pHs of 4.5, 5.8, and 7.1. The plants were fertilized using a nutrient solution, which was adjusted appropriately to the same pH. Plants in the control treatment were grown in the absence of the heavy metals mixture. The growth of the control plants was the same at the three pHs studied and the heavy metal stressed plants also showed similar behavior at each pHs. There were statistically significant differences (P<0.05) between the shoot length of the control treatment plants and the length of plants grown in the presence of the heavy metal mixture. Under the effects of the heavy metal mixture, nickel was the most accumulated element in the shoot tissue, with 437, 333, and 308 ppm at pH 7.1, 5.8, and 4.5, respectively. Cadmium was found to be second in accumulated concentrations with 202 ppm, 124 ppm, and 132 ppm at pH 7.1, 5.8, and 4.5, respectively, while zinc was third, followed by copper. The maximum relative uptakes (element in plant/element in soil-water-solution) were found to be 26 times for nickel, 23 times for cadmium, 12 times for zinc. and 6 times for copper. We considered these relations as indicative of the ability of alfalfa plants to take up elements from a soil matrix contaminated with a mixture of cadmium, copper, nickel, and zinc.

Plant Growth‐Promoting Bacteria Promote Copper and Iron Translocation from Root to Shoot in Alfalfa Seedlings

Abstract Plant growth‐promoting microorganisms have been utilized to promote plant potentialities and it has been reported that some bacterial strains can help certain plants to acquire iron (Fe) via siderophores. In this investigation it has been demonstrated that certain bacterial strains that synthesize siderophores influence copper (Cu) and Fe accumulation in alfalfa (Medicago sativa) seedlings mainly because they are able to modulate metal translocation from root to shoot. The roots of inoculated seedlings, growing in a solution containing 10 mg L−1 of CuSO4·5H2O plus 10 mg L−1 of FeCl3·6H2O, accumulated in a period of 8 days from 97 (UAP154 and UAP40) to 120 (U) mg of Cu per kg of dry matter (mean 110.41) and Fe from 126 (UAP154 and UAP40) to 151 (U, Avm, and CPMex46) (mean 139.26) while the non‐inoculated ones accumulated 103.8 and 146.9 mg of Cu and Fe per kg of dry mass, respectively. The accumulated Cu in stems of seedlings inoculated with the strains CPMex46, Avm, and UAP154 was 33, 24, and 0.3% more than the amount of Cu accumulated in stems of non‐inoculated seedlings (33.7 mg of metal per kg of dry mass). In the case of Fe, the stems of seedlings inoculated with the strains Avm, CPMex46, UAP40, and UAP154 accumulated 37, 31, 4, and 2% more Fe, respectively, as compared with the non‐inoculated seedlings (78.8 mg of metal per kg of dry mass). These results demonstrate that the strains CPMex46 and Avm improve both Cu and Fe translocation potential from root to shoot in alfalfa seedlings, fact that may be consider to promote the use of alfalfa crop for bioremediation applications.

Alfalfa growth promotion by bacteria grown under iron limiting conditions

Abstract This investigation has been conducted to compare and contrast the impact of 18 potentially plant growth-promoting bacterial strains, cultured in rich and iron-deficient minimal media, on alfalfa seed germination and seedling vigor. Our results showed that seed germination was improved by all of the bacterial strains grown in iron-deficient minimal medium. We also found that all the seeds inoculated with the bacterial strains grown in iron-deficient minimal medium produced seedlings with larger roots (55–66 mm) than the roots of uninoculated control plants (54.9 mm). Furthermore, most of the strains cultivated in iron-deficient minimal medium generated seedlings with larger roots than those seeds inoculated with microbial cells grown in iron-rich medium (37–59 mm). Overall, seeds inoculated with the strain U cultivated in iron-deficient minimal medium gave rise to plantlets with the greatest length (81 mm). On the other hand, seeds inoculated with bacterial cells grown under iron-rich media show significantly higher stem and root dry weight, which is an indication of the influence of the growth conditions on the plant growth-promoting ability of these microorganisms.

Modulation of uptake and translocation of iron and copper from root to shoot in common bean by siderophore-producing microorganisms

ABSTRACT Microbes have developed high-affinity uptake mechanisms to assimilate iron (Fe) and other metals such as aluminum (Al), gallium (Ga), chromium (Cr), and copper (Cu). Siderophores, which are metal chelating compounds, and membrane receptor proteins are involved in these specialized mechanisms. A few siderophore-producing microorganisms associated with plant roots also influence the uptake of some metals. In this study, the potential microbial-assisted Cu and Fe uptake by Phaseolus vulgaris (common bean) plants was evaluated. Seedlings of cultivated common bean varieties Bayo-INIFAP (B) and Negro-150 (N) and wild types yellowish (WY) and black (WB) were developed in the presence of a Cu and Fe solution and associated with the siderophore-producing microorganisms R. leguminosarumbv. Phaseoli (strains 19, 44, and 46); Pseudomonas fluorescens(strain Avm), and Azospirillum brasilense (strain 154). Seedlings of cultivated variety N and black wild type WB inoculated with the strain CPMex.44 accumulated 71% and 30% more Fe than the un-inoculated plants, respectively; however, the wild black bean accumulated the highest absolute amount of Fe (221.56 mg/kg of dry matter) as compared with the cultivated black variety N (126.16 mg/kg of dry matter) (P < 0.05). In the wild type WY seedlings, the highest Fe accumulation was observed when the seeds were inoculated with the Pseudomonas strain Avm (206 mg/kg of dry matter) (P < 0.05). The interaction of Pseudomonas strain Avm with seedlings of the cultivated B variety and the wild type WB promoted the highest accumulation of Cu (51 and 54 mg/kg of dry matter, respectively), 7 and 14 mg more than in the respective non-inoculated seedlings. No promotion of Fe accumulation was observed in the seedlings of the cultivated B variety and in roots; instead, less Fe was accumulated. The wild type WY did not show any improvement in Cu accumulation. In this study, Rhizobiumstrains promoted Fe but not Cu uptake in P. vulgaris seedlings while Pseudomonas strains promoted the uptake of both Cu and Fe.

Absorption and emission spectroscopic investigation of the phyto-extraction of europium(III) nitrate from aqueous solutions by alfalfa biomass

Abstract Europium(III) is a common product found in nuclear wastes. Recent investigations into the use of europium compounds as cancer therapy treatments have proven promising. In this study, europium(III) nitrate binding studies were performed using unmodified and esterified alfalfa biomass. Batch experiments included pH profile studies and X-ray absorption spectroscopy (XAS) inspection to determine the functional groups responsible for the binding of europium(III) nitrate on alfalfa. Results from the pH profile study showed that approximately 80% of the europium(III) nitrate bound to the native alfalfa biomass while the esterified biomass showed approximately 40% binding at pH 5. XAS consists of two complementary components: X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XAS experiments were performed using the europium L III edge which had an energy of 6.977 KeV. The XANES spectra showed that there were some changes in the characteristics of the europium(III) nitrate when bound to the modified and unmodified alfalfa biomass. No change in the europium(III) oxidation state was observed after europium(III) binding to the alfalfa biomass. EXAFS spectra showed that europium(III) nitrate binds to the alfalfa biomass via a nitrogen or oxygen ligand with bond lengths ranging from 2.44 to 2.49 A. However, chemical esterification experiments show that oxygen may be the primary ligand for coordination. The coordination numbers for all samples and compounds tested were approximately 9.