Gradient NMR Method for Studies of Water Translational Diffusion in Plants

Abstract

The review of a retrospective nature shows the stages of development of the spin-echo NMR method with constant and pulsed gradient of the magnetic field (gradient NMR) for the study of water diffusion in plant roots. The history of the initial use of gradient NMR for plants, in which it was not possible to experimentally confirm the bound state of water in cells, is described. The work presents the main ideas on which the technology of measuring diffusion by the spin-echo NMR method is built. Special attention is paid to the manifestations and record of the restricted diffusion phenomenon, permeability of membranes, along with the finite formulae used in real experiments. As examples, it gives the non-trivial results of studies of water transfer in roots through the symplastic system, from cell to cell through intercellular contacts with plasmodesmata, through aquaporins, transfer under the influence of changes in external pressure, and the composition of the gas atmosphere.

Keywords: gradient spin-echo NMR method; plant roots; water diffusion.

Figure 6

Tandem inclusion of pulse sequences of measurement of relaxation (zero-method) and diffusion (adapted from [51]).

Figure 1

Scheme of water movement between root cells in the radial direction: (1) Apoplasmic way through the cell walls; (2) symplasmic way on plasmodesmata, cytoplasm; (3) cell-to-cell way through tonoplast, cytoplasm, plasmalemma, cell walls.

Figure 2

Two-pulse Hahn method with a pulsed magnetic field gradient (PGSE—pulse gradient spin-echo).

Figure 3

Sequence of stimulated echo with pulsed magnetic field gradient (PGSTE).

Figure 4

Schematic behavior of R factor from $\left({\delta }^2{g}^2\right)$ for the case of diffusion in a free volume (straight line (4)) and through narrow pores with variation of diffusion time (10).

Figure 5

Dependence of relative self-diffusion coefficient on observation time 2$\tau$ for Zea mays (1) and for frog liver (2) at 25 °C (Adapted from [4]).

Figure 7

Schematic image of a simple plasmodesma. ([57]).

Figure 8

Dependence of water flow I_v through plasmodesma depending on the opening of the cervical constriction from the position of full coverage of the desmotubule, r_min = 0 to full opening, r_max. The dotted line corresponds to the situation of the adsorption potential of plasmodesmata walls [58].

Figure 9

Typical dependence R ($b$ ($b={\gamma }^2{\delta }^2{g}^2{t}_d$) for root segments normally and under the influence of Gd DTPA and GdCl₃.

Figure 10

Schematic representation of the cell chain divided into zones: I—plasmodesmata; II—tonoplast; III—vacuole [65].

Figure 11

Diffusion decay of echo in wheat roots in the normal conditions (decomposition into three exponents, (q² t_d =${\gamma }^2{\delta }^2{g}^2{t}_{d },$ t_d = 100 mc) [71].

Figure 12

Dependencies D₁, D₂, D₃ on diffusion time if there are manganese paramagnetic ions in root apoplast (MnCl₂, 10 mМ, 15 min) [71].

Figure 13

Model of transfer by a vacuolar symplast through desmotubule: (1) Apoplasmic way through the cells walls; (2) symplast way on cytoplasm plasmodesmata; (3) cell-to-cell way through tonoplast, cytoplasma, plasmalemma, and cell walls; (4) symplast vacuolar way through desmotubula plasmadesmata and vacuole.

Figure 14

Def dependencies on time (in minutes) of PEG-6000 osmotic action for roots in normal conditions (1) and (2) roots pre-treated with aquaporin blocker (15 min, 0.1 Mm HgCl₂ at t_d =100 mc), [80].

Figure 15

The dip in the curve decay of magnetization near 0.8 min after a fast (pulse) supply of the PEG-6000 osmotic to the meristem of the root, (${\delta }^2{g}^2{t}_d=const)$ [80].

Figure 16

Temperature dependence of the diffusion coefficient of cytoplasmic water in the control (■) and under the effect of gadolinium (○), BDM (Δ), and of bulk water (●) [53].

Figure 17

Temperature dependence of Δx in the control (■) and under the effect of gadolinium (○), BDM (Δ) [53].

Figure 18

The increase (in per cent) in root segment length 4.5 h after cutting off at 23 °C and the atmosphere pressure (control) and under the treatment with the air pressure of MPa [94].

Figure 19

Time course of elongation (in percent) of the intact roots at 23 °C under the atmosphere pressure (solid squares) and under the impact of external air pressure of 2 MPa (open circles). After 6h of 2 MPa pressure impact (region 1) the pressure was released to the level of atmosphere (region 2) [94].

Figure 20

Diffusion decay for root segments: Control (solid square), 20 min treatment with sodium azide of different concentration: 0.01 M (open square), 0.001 M (open circle), 0.0005 M (open triangle) [94].

Figure 21

The dependence of the effective diffusion coefficient on the diffusion time for intact seedling roots (solid squares) and the result of the renormalization of D_ef(t_d) into the dependence D_ef2(t_d) as a function of t_d⁻¹ [94].

Figure 22

Time dependence of the ratio of effective self-diffusion coefficient (D_ef) in maize roots under impact of different concentrations of CO₂ to the control value of D_ef (D_{ef control} before CO₂ enrichment): Open squares—dynamics of D_ef/D_{ef control} under impact of CO₂ 800 ppm; open circles—dynamics of D_ef/D_{ef control} under impact of CO₂ 1200 ppm [96].

Figure 23

Diffusional decays for roots of intact maize plants in control (ambient CO₂ 400 ppm) (open squares), after 2 h of roots incubation in 25 mM solute of GdDTPA (open circles) and following an increasing CO₂ concentration to 800 ppm (open triangles), $(b={ \mathsf{\gamma }}^2{\mathsf{\delta }}^2{\mathrm{g}}^2{\mathrm{t}}_{\mathrm{d}}$) [96].

Figure 24

Diffusion decays of water magnetization in cells of intact corn roots in control and 2 h after increasing the nitrogen concentration N₂ in the leaf zone up to 100% under normobaric conditions in the atmosphere ($b={ \mathsf{\gamma }}^2{\mathsf{\delta }}^2{\mathrm{g}}^2{\mathrm{t}}_{\mathrm{d}}$) [96].

Figure 25

Diffusion decays of water magnetization in cells of intact corn roots in control and 30 min after an increase in the O₂ concentration in the leaf zone up to 40% and 60% under normobaric conditions in the atmosphere ($b={ \mathsf{\gamma }}^2{\mathsf{\delta }}^2{\mathrm{g}}^2{\mathrm{t}}_{\mathrm{d}}$) [96].