A 1H NMR study of water flow in Phaseolus vulgaris L. roots treated with nitrate or ammonium

Abstract

The effect of N nutrition on root xylem (water) flow in Phaseolus vulgaris was studied by using the 1 H NMR flow imaging technique. Plants pre-cultivated on CaSO 4 -solution were transferred to NMR-compatible split-root cuvettes filled with halfstrength nitrate medium (2.5 mM). After 6 days fullstrength (5 mM) nitrate medium was supplied to both compartments (NN treatment), or only to one compartment, whereas the other one was perfused with full-strength (5 mM) ammonium medium (NA treatment). Imaging was performed 7-8 days later. Root growth, xylem flow velocity and xylem pressure (measured with the xylem pressure probe) were largely unaffected by N nutrition. Under NA conditions, volume flow was significantly lower in ammonium-compared to nitrate-fed roots due to a reduced number of functional xylem elements. This was apparently not related to anatomical differences nor to an enhanced number of cavitated vessels in ammonium-fed roots. Vessels in these roots may become dysfunctional by clogging to prevent cavitation.

Changes in 15NO3- Availability and Transpiration Rate Are Associated With a Rapid Diurnal Adjustment of Anion Contents as Well as 15N and Water Fluxes Between the Roots and Shoots

“…A better understanding of the dynamic interactions between nitrate and water fluxes submitted to different transpiration rates is becoming critical for agriculture because of the worldwide increase in food demand, climate change and the increase in fertilizer costs (Good et al, 2004). Unraveling these interactions requires the development of non-invasive methods avoiding excised roots and/or pressurization of the root system, in order to analyze simultaneously the dynamic interactions of water and nitrate fluxes in intact transpiring plants during a day–night cycle (Windt et al, 2006; Schulze-Till et al, 2009; Wegner, 2015). Indeed, the invasive approaches used to date on excised roots lead to the breakdown of water relations in the plant and destroy the signal flows between shoots and roots.…”

“…So far, these methods have been used in intact plants with a low temporal resolution (day-to-week) and without the aid of 13 NO 3 - or 15 NO 3 - tracers (Shaner and Boyer, 1976; Schulze and Bloom, 1984). However, the techniques such as psychrometry, gravimetry, potometer and nuclear magnetic resonance imaging (MRI and 1 H NMR) allow the measurements of water flow by using high temporal resolution (Van Ieperen and Madery, 1994; Kockenberger et al, 1997; Peuke et al, 2001; Li and Shao, 2003; Windt et al, 2006; Schulze-Till et al, 2009). Likewise, the use of 13 NO 3 - and 15 NO 3 - tracers and PETIS method (Positron Emitting Tracer Imaging System) allows to measure the 15 N translocation and nitrate flow in the xylem of intact plants over short periods of time (Clarkson et al, 1996; Kawachi et al, 2002).…”

“…The root hydraulic properties dependence on nitrate availability must also be reconsidered because of the nitrate effect on the total volume flow of water through xylem elements observed by 1 H NMR method in split-root experiments (Schulze-Till et al, 2009). Indeed, NMR studies showed that nitrate treatment significantly increases the water flow rates, due to an increase in the number of xylem functional elements for water transport in the root cross section.…”

Interplay of Water and Nutrient Transport: A Whole-Plant Perspective

“…However, when linking this effect to the response of the whole plant, complexity increases. In split-root experiments on bean with part of the root supplied with nitrate and the other provided with ammonium, Schulze-Till et al (2009) using the MRT technology, observed higher rates of water flow in the nitrate-fed roots due to a larger number of vessels per root contributing to flow than in those provided with ammonium. Flow velocity and xylem pressure of conducting xylem elements did not differ much, though, and anatomical properties were also unaffected by the N-form.…”

“…From the data, a flow velocity can be calculated; by multiplication with the conducting area (that can be obtained from flow images) volume flow becomes accessible (e.g. Schulze-Till et al 2009). …”