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Title: Emerging investigator series: entrapment of uranium–phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site
We investigated the mechanisms of uranium (U) uptake by Tamarix (salt cedars) growing along the Rio Paguate, which flows throughout the Jackpile mine near Pueblo de Laguna, New Mexico. Tamarix were selected for this study due to the detection of U in the roots and shoots of field collected plants (0.6–58.9 mg kg −1 ), presenting an average bioconcentration factor greater than 1. Synchrotron-based micro X-ray fluorescence analyses of plant roots collected from the field indicate that the accumulation of U occurs in the cortex of the root. The mechanisms for U accumulation in the roots of Tamarix were further investigated in controlled-laboratory experiments where living roots of field plants were macerated for 24 h or 2 weeks in a solution containing 100 μM U. The U concentration in the solution decreased 36–59% after 24 h, and 49–65% in two weeks. Microscopic and spectroscopic analyses detected U precipitation in the root cell walls near the xylems of the roots, confirming the initial results from the field samples. High-resolution TEM was used to study the U fate inside the root cells, and needle-like U–P nanocrystals, with diameter <7 nm, were found entrapped inside vacuoles in cells. EXAFS shell-by-shell fitting suggest that U is associated with carbon functional groups. The preferable binding of U to the root cell walls may explain the U retention in the roots of Tamarix , followed by U–P crystal precipitation, and pinocytotic active transport and cellular entrapment. This process resulted in a limited translocation of U to the shoots in Tamarix plants. This study contributes to better understanding of the physicochemical mechanisms affecting the U uptake and accumulation by plants growing near contaminated sites. more »« less
Hu, Ruifang; Limmer, Matthew A.; Seyfferth, Angelia L.(
, Plant and Soil)
AbstractBackground and aims
Rice is prone to Cd uptake under aerobic soil conditions primarily due to the OsNramp5 Mn transport pathway. Unlike Cd, Mn availability in rice paddies decreases as redox potential increases. We tested whether increasing Mn concentrations in solution would decrease Cd accumulation in rice through competition between Mn and Cd for uptake and/or suppression ofOsNramp5expression.
Methods
Rice was grown to maturity under Mn concentrations that spanned three orders of magnitude (0.30 to 37 μM) that corresponded to free Mn2+activities of 10–7.9to 10–5.0 M while free Cd2+activity was held as constant as achievable (10–10.2to 10–10.4 M). Plant biomass and elemental concentrations were measured in roots and shoots at each stage. Fold changes in the expression ofOsNramp5,OsCd1,OsHMA3,OsCCX2, andOsYSL6genes in vegetative and grain-filling stages of rice plants were determined.
Results
Competition between Mn and Cd for root uptake and accumulation in shoots was observed at the highest concentration of Mn tested.OsNramp5expression was significantly higher in rice plants at the vegetative stage compared to the grain-filling stage, whileOsCd1andOsHMA3showed the opposite. Solution Mn concentrations previously thought to be tolerable by rice grown to the vegetative stage led to Mn toxicity as plants matured.
Conclusions
Mn competes with Cd during uptake into rice withOsNramp5expression unaffected. Different translocation paths may occur for Mn and Cd within the rice plant and over the rice life cycle, withOsCCX2correlated with shoot Cd concentration.
Glutaredoxins (GRXs) are small oxidoreductase enzymes that can reduce disulfide bonds in target proteins. The class III GRX gene family is unique to land plants, andArabidopsis thalianahas 21 class III GRXs, which remain largely uncharacterized. About 80% ofA. thalianaclass III GRXs are transcriptionally regulated by nitrate, and several recent studies have suggested roles for these GRXs in nitrogen signaling. Our objective was to functionally characterize two nitrate‐induced GRX genes,AtGRXS5andAtGRXS8, defining their roles in signaling and development in theA. thalianaroot. We demonstrated thatAtGRXS5andAtGRXS8are primarily expressed in root and shoot vasculature (phloem), and that the corresponding GRX proteins display nucleo‐cytosolic subcellular localization. Ectopic expression ofAtGRXS8in transgenic plants caused major alterations in root system architecture: Normal primary root development, but a near absence of lateral roots. RNA sequencing demonstrated that the roots ofAtGRXS8‐overexpressing plants show strongly reduced transcript abundance for many primary nitrate response genes, including the major high‐affinity nitrate transporters. Correspondingly, high‐affinity nitrate uptake and the transport of nitrate from roots to shoots are compromised inAtGRXS8‐overexpressing plants. Finally, we demonstrated that the AtGRXS8 protein can physically interact with the TGA1 and TGA4 transcription factors, which are central regulators of early transcriptional responses to nitrate inA. thalianaroots. Overall, these results suggest thatAtGRXS8acts to quench both transcriptional and developmental aspects of primary nitrate response, potentially by interfering with the activity of the TGA1 and TGA4 transcription factors.
Albano, Lucas J.; Turetsky, Merritt R.; Mack, Michelle C.; Kane, Evan S.(
, Plant and Soil)
null
(Ed.)
Aims
Climate warming in northern ecosystems is triggering widespread permafrost thaw, during which deep soil nutrients, such as nitrogen, could become available for biological uptake. Permafrost thaw shift frozen organic matter to a saturated state, which could impede nutrient uptake. We assessed whether soil nitrogen can be accessed by the deep roots of vascular plants in thermokarst bogs, potentially allowing for increases in primary productivity.
Methods
We conducted an ammonium uptake experiment on Carex aquatilis Wahlenb. roots excavated from thermokarst bogs in interior Alaska. Ammonium uptake capacity was compared between deep and shallow roots. We also quantified differences in root ammonium uptake capacity and plant size characteristics (plant aboveground and belowground biomass, maximum shoot height, and maximum root length) between the actively-thawing margin and the centre of each thermokarst bog as a proxy for time-following-thaw.
Results
Deep roots had greater ammonium uptake capacity than shallow roots, while rooting depth, but not belowground biomass, was positively correlated with aboveground biomass. Although there were no differences in aboveground biomass between the margin and centre, our findings suggest that plants can benefit from investing in the acquisition of resources near the vertical thaw front.
Conclusions
Our results suggest that deep roots of C. aquatilis can contribute to plant nitrogen uptake and are therefore able to tolerate anoxic conditions in saturated thermokarst bogs. This work furthers our understanding of how subarctic and wetland plants respond to warming and how enhanced plant biomass production might help offset ecosystem carbon release with future permafrost thaw.
Su, Shih-Heng; Levine, Howard G.; Masson, Patrick H.(
, Life)
Plants have been recognized as key components of bioregenerative life support systems for space exploration, and many experiments have been carried out to evaluate their adaptability to spaceflight. Unfortunately, few of these experiments have involved monocot plants, which constitute most of the crops used on Earth as sources of food, feed, and fiber. To better understand the ability of monocot plants to adapt to spaceflight, we germinated and grew Brachypodium distachyon seedlings of the Bd21, Bd21-3, and Gaz8 accessions in a customized growth unit on the International Space Station, along with 1-g ground controls. At the end of a 4-day growth period, seedling organ’s growth and morphologies were quantified, and root and shoot transcriptomic profiles were investigated using RNA-seq. The roots of all three accessions grew more slowly and displayed longer root hairs under microgravity conditions relative to ground control. On the other hand, the shoots of Bd21-3 and Gaz-8 grew at similar rates between conditions, whereas those of Bd21 grew more slowly under microgravity. The three Brachypodium accessions displayed dramatically different transcriptomic responses to microgravity relative to ground controls, with the largest numbers of differentially expressed genes (DEGs) found in Gaz8 (4527), followed by Bd21 (1353) and Bd21-3 (570). Only 47 and six DEGs were shared between accessions for shoots and roots, respectively, including DEGs encoding wall-associated proteins and photosynthesis-related DEGs. Furthermore, DEGs associated with the “Oxidative Stress Response” GO group were up-regulated in the shoots and down-regulated in the roots of Bd21 and Gaz8, indicating that Brachypodium roots and shoots deploy distinct biological strategies to adapt to the microgravity environment. A comparative analysis of the Brachypodium oxidative-stress response DEGs with the Arabidopsis ROS wheel suggests a connection between retrograde signaling, light response, and decreased expression of photosynthesis-related genes in microgravity-exposed shoots. In Gaz8, DEGs were also found to preferentially associate with the “Plant Hormonal Signaling” and “MAP Kinase Signaling” KEGG pathways. Overall, these data indicate that Brachypodium distachyon seedlings exposed to the microgravity environment of ISS display accession- and organ-specific responses that involve oxidative stress response, wall remodeling, photosynthesis inhibition, expression regulation, ribosome biogenesis, and post-translational modifications. The general characteristics of these responses are similar to those displayed by microgravity-exposed Arabidopsis thaliana seedlings. However, organ- and accession-specific components of the response dramatically differ both within and between species. These results suggest a need to directly evaluate candidate-crop responses to microgravity to better understand their specific adaptability to this novel environment and develop cultivation strategies allowing them to strive during spaceflight.
Rodriguez-Freire, Lucia, DeVore, Cherie L., El Hayek, Eliane, Berti, Debora, Ali, Abdul-Mehdi S., Lezama Pacheco, Juan S., Blake, Johanna M., Spilde, Michael N., Brearley, Adrian J., Artyushkova, Kateryna, and Cerrato, José M. Emerging investigator series: entrapment of uranium–phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site. Retrieved from https://par.nsf.gov/biblio/10213522. Environmental Science: Processes & Impacts 23.1 Web. doi:10.1039/D0EM00306A.
Rodriguez-Freire, Lucia, DeVore, Cherie L., El Hayek, Eliane, Berti, Debora, Ali, Abdul-Mehdi S., Lezama Pacheco, Juan S., Blake, Johanna M., Spilde, Michael N., Brearley, Adrian J., Artyushkova, Kateryna, & Cerrato, José M. Emerging investigator series: entrapment of uranium–phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site. Environmental Science: Processes & Impacts, 23 (1). Retrieved from https://par.nsf.gov/biblio/10213522. https://doi.org/10.1039/D0EM00306A
Rodriguez-Freire, Lucia, DeVore, Cherie L., El Hayek, Eliane, Berti, Debora, Ali, Abdul-Mehdi S., Lezama Pacheco, Juan S., Blake, Johanna M., Spilde, Michael N., Brearley, Adrian J., Artyushkova, Kateryna, and Cerrato, José M.
"Emerging investigator series: entrapment of uranium–phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site". Environmental Science: Processes & Impacts 23 (1). Country unknown/Code not available. https://doi.org/10.1039/D0EM00306A.https://par.nsf.gov/biblio/10213522.
@article{osti_10213522,
place = {Country unknown/Code not available},
title = {Emerging investigator series: entrapment of uranium–phosphorus nanocrystals inside root cells of Tamarix plants from a mine waste site},
url = {https://par.nsf.gov/biblio/10213522},
DOI = {10.1039/D0EM00306A},
abstractNote = {We investigated the mechanisms of uranium (U) uptake by Tamarix (salt cedars) growing along the Rio Paguate, which flows throughout the Jackpile mine near Pueblo de Laguna, New Mexico. Tamarix were selected for this study due to the detection of U in the roots and shoots of field collected plants (0.6–58.9 mg kg −1 ), presenting an average bioconcentration factor greater than 1. Synchrotron-based micro X-ray fluorescence analyses of plant roots collected from the field indicate that the accumulation of U occurs in the cortex of the root. The mechanisms for U accumulation in the roots of Tamarix were further investigated in controlled-laboratory experiments where living roots of field plants were macerated for 24 h or 2 weeks in a solution containing 100 μM U. The U concentration in the solution decreased 36–59% after 24 h, and 49–65% in two weeks. Microscopic and spectroscopic analyses detected U precipitation in the root cell walls near the xylems of the roots, confirming the initial results from the field samples. High-resolution TEM was used to study the U fate inside the root cells, and needle-like U–P nanocrystals, with diameter <7 nm, were found entrapped inside vacuoles in cells. EXAFS shell-by-shell fitting suggest that U is associated with carbon functional groups. The preferable binding of U to the root cell walls may explain the U retention in the roots of Tamarix , followed by U–P crystal precipitation, and pinocytotic active transport and cellular entrapment. This process resulted in a limited translocation of U to the shoots in Tamarix plants. This study contributes to better understanding of the physicochemical mechanisms affecting the U uptake and accumulation by plants growing near contaminated sites.},
journal = {Environmental Science: Processes & Impacts},
volume = {23},
number = {1},
author = {Rodriguez-Freire, Lucia and DeVore, Cherie L. and El Hayek, Eliane and Berti, Debora and Ali, Abdul-Mehdi S. and Lezama Pacheco, Juan S. and Blake, Johanna M. and Spilde, Michael N. and Brearley, Adrian J. and Artyushkova, Kateryna and Cerrato, José M.},
editor = {null}
}
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