- NSF-PAR ID:
- 10031113
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- Volume:
- 15
- Issue:
- 9
- ISSN:
- 1541-5856
- Page Range / eLocation ID:
- 766 to 781
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
null (Ed.)Symbiotic nitrogen fixation is a complex and regulated process that takes place in root nodules of legumes and allows legumes to grow in soils that lack nitrogen. Nitrogen is mostly acquired from the soil as nitrate and its level in the soil affects nodulation and nitrogen fixation. The mechanism(s) by which legumes modulate nitrate uptake to regulate nodule symbiosis remain unclear. In Medicago truncatula , the MtNPF1.7 transporter has been shown to control nodulation, symbiosis, and root architecture. MtNPF1.7 belongs to the nitrate/peptide transporter family and is a symporter with nitrate transport driven by proton(s). In this study we combined in silico structural predictions with in planta complementation of the severely defective mtnip-1 mutant plants to understand the role of a series of distinct amino acids in the transporter’s function. Our results support hypotheses about the functional importance of the ExxE(R/K) motif including an essential role for the first glutamic acid of the motif in proton(s) and possibly substrate transport. Results reveal that Motif A, a motif conserved among major facilitator transport (MFS) proteins, is essential for function. We hypothesize that it participates in intradomain packing of transmembrane helices and stabilizing one conformation during transport. Our results also question the existence of a putative TMH4-TMH10 salt bridge. These results are discussed in the context of potential nutrient transport functions for MtNPF1.7. Our findings add to the knowledge of the mechanism of alternative conformational changes as well as symport transport in NPFs and enhance our knowledge of the mechanisms for nitrate signaling.more » « less
-
more » « less
ABSTRACT Cell-division-plane orientation is critical for plant and animal development and growth. TANGLED1 (TAN1) and AUXIN-INDUCED IN ROOT CULTURES 9 (AIR9) are division-site-localized microtubule-binding proteins required for division-plane positioning. The single mutants tan1 and air9 of Arabidopsis thaliana have minor or no noticeable phenotypes, but the tan1 air9 double mutant has synthetic phenotypes including stunted growth, misoriented divisions and aberrant cell-file rotation in the root differentiation zone. These data suggest that TAN1 plays a role in non-dividing cells. To determine whether TAN1 is required in elongating and differentiating cells in the tan1 air9 double mutant, we limited its expression to actively dividing cells using the G2/M-specific promoter of the syntaxin KNOLLE (pKN:TAN1–YFP). Unexpectedly, in addition to rescuing division-plane defects, expression of pKN:TAN1–YFP rescued root growth and cell file rotation defects in the root-differentiation zone in tan1 air9 double mutants. This suggests that defects that occur in the meristematic zone later affect the organization of elongating and differentiating cells.
-
more » « less
Abstract Riparian zones, the interfaces between land and stream, perform vital ecosystem functions including transformation and retention of nutrients and sediment moving across the landscape. Although many studies assess transport through and transformation of materials in riparian zones, less is known about the direct influence of precipitation falling on these zones on material retention and transport. Additionally, few experiments can compare riparian retention to stream‐channel retention.
We present a novel experimental approach to assess retention of nitrate entering as precipitation in riparian zones and compare riparian retention and movement of nitrate, other ions, sediments to and within the adjacent stream channel. We simulated an intense precipitation event with15N‐labelled nitrate as a bioactive solute and bromide as an inert tracer. This method extends tracer release approaches applied to streams worldwide and links it to processes at the aquatic/ terrestrial interface. It further allows determination of movement of materials into streams from bankside precipitation.
The riparian zone removed or retained a greater proportion of nitrate than the stream relative to bromide; over half the added bromide reached the stream through a few metres of riparian zone, compared to only 0.2% of the added nitrate. Of the 0.2% that reached the stream, 30% of that nitrate was removed or retained by instream processes after travelling 60 downstream. Roughly 10% of the total15N addition ended up sequestered in the above‐ground portions of the riparian grasses by the end of the growing season, and very little of it was recovered from the soil. We saw little evidence of bulk transport of other ions or sediment from this riparian soil to the stream.
Our data are consistent with the concept of high nitrate retention in vegetated riparian zones, even for nitrate falling directly upon them in the form of atmospheric deposition in precipitation.
