C. A. Sanchez

Genetic Manipulation of a "Vacuolar" H+ -PPase: From Salt Tolerance to Yield Enhancement under Phosphorus-Deficient Soils

Plant scientists face the difficult challenge of increasing food production without further degradation of the environment. In order to protect drinking water resources and prevent the proliferation of harmful algal blooms and “dead zones” in coastal marine ecosystems, it is imperative to reduce

Escherichia coli survival in lettuce fields following its introduction through different irrigation systems

Aims:  This study aimed to assess the contamination risk of Escherichia coli in commercial lettuce grown under three different irrigation systems (overhead sprinkler, subsurface drip and surface furrow).

Point sources of emerging contaminants along the Colorado River Basin: Source water for the arid Southwestern United States

Emerging contaminants (ECs) (e.g., pharmaceuticals, illicit drugs, personal care products) have been detected in waters across the United States. The objective of this study was to evaluate point sources of ECs along the Colorado River, from the headwaters in Colorado to the Gulf of California. At selected locations in the Colorado River Basin (sites in Colorado, Utah, Nevada, Arizona, and California), waste stream tributaries and receiving surface waters were sampled using either grab sampling or polar organic chemical integrative samplers (POCIS). The grab samples were extracted using solid-phase cartridge extraction (SPE), and the POCIS sorbents were transferred into empty SPEs and eluted with methanol. All extracts were prepared for, and analyzed by, liquid chromatography-electrospray-ion trap mass spectrometry (LC-ESI-ITMS). Log D(OW) values were calculated for all ECs in the study and compared to the empirical data collected. POCIS extracts were screened for the presence of estrogenic chemicals using the yeast estrogen screen (YES) assay. Extracts from the 2008 POCIS deployment in the Las Vegas Wash showed the second highest estrogenicity response. In the grab samples, azithromycin (an antibiotic) was detected in all but one urban waste stream, with concentrations ranging from 30ng/L to 2800ng/L. Concentration levels of azithromycin, methamphetamine and pseudoephedrine showed temporal variation from the Tucson WWTP. Those ECs that were detected in the main surface water channels (those that are diverted for urban use and irrigation along the Colorado River) were in the region of the limit-of-detection (e.g., 10ng/L), but most were below detection limits.

Enhanced Proton Translocating Pyrophosphatase Activity Improves Nitrogen Use Efficiency in Romaine Lettuce

A simple genetic manipulation triggers enhanced nitrogen use efficiency in lettuce. Plant nitrate (NO3−) acquisition depends on the combined activities of root high- and low-affinity NO3− transporters and the proton gradient generated by the plasma membrane H+-ATPase. These processes are coordinated with photosynthesis and the carbon status of the plant. Here, we present the characterization of romaine lettuce (Lactuca sativa ‘Conquistador’) plants engineered to overexpress an intragenic gain-of-function allele of the type I proton translocating pyrophosphatase (H+-PPase) of Arabidopsis (Arabidopsis thaliana). The proton-pumping and inorganic pyrophosphate hydrolytic activities of these plants are augmented compared with control plants. Immunohistochemical data show a conspicuous increase in H+-PPase protein abundance at the vasculature of the transgenic plants. Transgenic plants displayed an enhanced rhizosphere acidification capacity consistent with the augmented plasma membrane H+-ATPase proton transport values, and ATP hydrolytic capacities evaluated in vitro. These transgenic lines outperform control plants when challenged with NO3− limitations in laboratory, greenhouse, and field scenarios. Furthermore, we report the characterization of a lettuce LsNRT2.1 gene that is constitutive up-regulated in the transgenic plants. Of note, the expression of the LsNRT2.1 gene in control plants is regulated by NO3− and sugars. Enhanced accumulation of 15N-labeled fertilizer by transgenic lettuce compared with control plants was observed in greenhouse experiments. A negative correlation between the level of root soluble sugars and biomass is consistent with the strong root growth that characterizes these transgenic plants.

Perchlorate in the Feed-Dairy Continuum of the Southwestern United States

Perchlorate has the potential to cause thyroid dysfunction by inhibiting iodide uptake by the sodium iodide symporter. Perchlorate-contaminated waters may lead to human exposure through drinking water and food chain transfer in crops by way of irrigation water. Perchlorate has been found in dairy milk collected nationally and internationally. This study was conducted to evaluate perchlorate in the feed-dairy continuum in the southwestern United States. All feed products collected at dairies in this study had detectable levels of perchlorate as analyzed by ion chromatography-tandem mass spectrometry. The calculated total perchlorate intake across dairies ranged from 1.9 to 12.7 mg/cow per day. The variation in total perchlorate intake across dairies was largely associated with variation in forage and silage products. Alfalfa products were the single most important source of perchlorate intake variability among dairies. The estimated perchlorate intake from drinking water ranged from 0.01 mg per cow per day and was generally less than 2% of the total perchlorate intake. The perchlorate content of milk ranged from 0.9 to 10.3 microg/L and was similar to levels reported by the Food and Drug Administrations Total Diet Study. The perchlorate content of milk was significantly related to the presence of perchlorate in feed but the variation of perchlorate in milk could not be explained by feed intake alone.

Formation of hydroxyapatite in soils using calcium citrate and sodium phosphate for control of strontium migration

Summary 90Sr contamination is a major problem at several U.S. sites. At some sites, 90Sr has migrated deep underground making site remediation difficult. In this paper, we describe a novel method for precipitation of hydroxyapatite, a strong sorbent for 90Sr, in soil. The method is based on mixing a solution of calcium citrate and sodium phosphate in soil. As the indigenous soil microorganisms mineralize the citrate, the calcium is released and forms hydroxyapatite. Soil, taken from the Albuquerque desert, was treated with a sodium phosphate solution or a sodium phosphate/calcium citrate solution. TEM and EDS were used to identify hydroxyapatite with CO32- substitutions, with a formula of (Ca4.8Na0.2)[(PO4)2.8(CO3)0.2](OH), in the soil treated with the sodium phosphate/calcium citrate solution. Untreated and treated soils were used in batch sorption experiments for Sr uptake. Average Sr uptake was 19.5, 77.0 and 94.7% for the untreated soil, soil treated with sodium phosphate, and soil with apatite, respectively. In desorption experiments, the untreated soil, phosphate treated soil and apatite treated soil released an average of 34.2, 28.8 and 4.8% respectively. The results indicate the potential of forming apatite in soil using soluble reagents for retardation of radionuclide migration.

Sorption of Np(V) by synthetic hydroxyapatite

Abstract The sorption of Np(V) to synthetic hydroxyapatite was determined in batch experiments in a 0.1M NaClO4 solution. The hydroxyapatite used was of high purity as determined by SEM, EDS, XRD, FT-IR and ICP-MS analysis. Results from kinetic experiments with an initial Np(V) concentration of 1×10-7 to 1×10-6M indicate the sorption process is relatively fast with more than 90 of the Np(V) being sorbed in approximately 3 hours. Equilibrium experiments performed over the pH range of 6 to 11 indicated sorption is strongly pH dependent with distribution coefficients, Kd values (mL/g), increasing from 123L/mole at pH 6 to 69200L/mole at pH 8.5. Kd values are observed to decrease as pH further increases. Data points over a range of Np(V) concentrations were collected at pH 8 and fitted to the Langmuir isotherm model for simple adsorption. The Langmuir equation gave an excellent representation of the data. Langmuir parameters were determined to be Ca=0.032mole/mole and K=1.22×106L/mole, indicating the high affinity of hydroxyapatite for Np(V) adsorption.

Perchlorate exposure from food crops produced in the lower Colorado River region.

The Colorado River shows low levels of perchlorate derived from aerospace- and defense-related fuel industries once located near the Las Vegas Wash. At sufficiently high dosages perchlorate can disrupt thyroid function by inhibiting uptake of iodide. The Colorado River is the primary source of irrigation water for most food crops grown in Southern California and Southwestern Arizona. The objective of this study was to evaluate potential perchlorate exposure from food crops produced in the lower Colorado River region (LCRR). The major food commodities produced in the region were sampled and perchlorate levels were determined by ion chromatography followed by detection using either conductivity or tandem mass spectrometry, depending on analyte levels. The Monte Carlo module of the Dietary Exposure Evaluation Model (DEEM™) was used to derive an estimate of the 2-day average perchlorate intakes. Data were derived assuming that individuals residing in the LCRR get their fruits and vegetables from within the LCRR as well as from other areas in the United States, or assuming individuals living in the LCRR get their fruits and vegetables from the LCRR only. Perchlorate exposure estimates derived in this study are comparable to exploratory estimates by the US Food and Drug Administration. For infants and children, over 50% of the estimated perchlorate exposure was from milk. The relative impact of vegetables and fruit toward perchlorate exposure increased by age through adulthood. Cumulative perchlorate exposure estimates based on this hypothetical analysis could approach or exceed the NAS reference dose (RfD) for some population groups as drinking water levels exceeded 6 μg/l. However, few individuals are exposed to perchlorate in drinking water at levels above 4 μg/l in the United States and very few would be exposed to perchlorate levels exceeding the RfD, whether consuming food crops from within or outside the LCRR.

Effects of nitrogen and foliar biomass on population parameters of cabbage insects

The effects of different nitrogen (N) fertilization rates (0, 45, 90, and 168 kg N/ha), plant nitrogen concentration, and plant biomass on abundance and population growth of diamondback moth, Plutella xylostella (L.), cabbage looper, Trichoplusia ni (Hübner), cabbage budworm, Hellula phidilealis (Walker), imported cabbageworm, Artogeia rapae (L.), and cross‐striped cabbageworm, Evergestis rimosalis (Guenée), were investigated in Homestead and Sanford, Florida in 1987. The effects of these factors on the parasitization of P. xylostella were also examined. In Homestead, abundance of most insect pests and parasitized P. xylostella increased with an increase in the level of N applied and with an increase in plant biomass. Similar results were found in Sanford, although results were not consistently significant. Abundance of most insect pests was significantly positively correlated with plant N concentration. Multiple regression analyses indicated that foliar biomass was significantly more important than N fertilization rate and subsequent plant N concentration at predicting abundance of insect pests and parasitized P. xylostella on cabbage.

Comparison of various soil drying techniques on extractable nutrients

Abstract Changes that take place in soil samples as they are dried and stored may pose serious problems in predicting plant responses compared to moist soils under field conditions. The effects of drying and storage techniques (air, microwave, oven‐drying, and frozen) on the levels of Mehlich‐I‐extractable nutrients were evaluated in six diverse soils. The use of microwave‐drying as a rapid soil drying method prior to chemical analysis was also evaluated. Drying and freezing caused large changes in the levels of extractable nutrients in all soils. The effects of drying were dependent on drying intensity and the initial physical and chemical properties of the soil. Many of the changes in the levels of extractable nutrients resulting from drying the soil appear to be associated with the oxidation of organic matter (OM) and changes in hydration state and redox status of different soil components. Results from this study also indicate that microwave drying of soils has potential for rapid drying of soil sampl...