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SUMMARY Root systems are uniquely adapted to fluctuations in external nutrient availability. In response to suboptimal nitrogen conditions, plants adopt a root foraging strategy that favors a deeper and more branched root architecture, enabling them to explore and acquire soil resources. This response is gradually suppressed as nitrogen conditions improve. However, the root hairless mutantbuzzinBrachypodium distachyonshows a constitutive nitrogen‐foraging phenotype with increased root growth and root branching under nitrate‐rich conditions. To investigate how this unique root structure and root hair morphology in thebuzzmutant affects nitrate metabolism, we measured the expression of nitrate‐responsive genes, nitrate uptake and accumulation, nitrate reductase activity, and nitrogen use efficiency. We found that nitrate responses were upregulated by low nitrate conditions inbuzzrelative to wild type and correlated with increased expression of nitrate transport genes. In addition,buzzmutants showed increased nitrate uptake and a higher accumulation of nitrate in shoots. Thebuzzmutant also showed increased nitrate reductase activity in the shoots under low nitrate conditions. However, developmentally mature wild‐type andbuzzplants grown under low nitrate had similar nitrogen use efficiencies. These findings suggest thatBUZZinfluences nitrate signaling and that enhanced responsiveness to nitrate is required inbuzzseedlings to compensate for the lack of root hairs. These data question the importance of root hairs in enhancing nitrate uptake and expand our understanding of how root hairs in grasses affect physiological responses to low nitrate availability.
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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.
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- PAR ID:
- 10213522
- Date Published:
- Journal Name:
- Environmental Science: Processes & Impacts
- Volume:
- 23
- Issue:
- 1
- ISSN:
- 2050-7887
- Page Range / eLocation ID:
- 73 to 85
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0EM00306A
