Abstract
Time domain nuclear magnetic resonance (TD–NMR) has been widely applied in plant science in the last four decades. Several TD–NMR instruments and methods have been developed for laboratory, green-house, and field studies. This mini-review focuses on the recent TD–NMR pulse sequences applied in plant science. One of the sequences measures the transverse relaxation time (T2) with minimal sample heating, using a lower refocusing flip angle and consequently lower specific absorption rate than that of conventional CPMG. Other sequences are based on a continuous wave free precession (CWFP) regime used to enhance the signal-to-noise ratio, to measure longitudinal (T1) and transverse relaxation time in a single shot experiment, and as alternative 2D pulse sequences to obtain T1–T2 and diffusion-T1 correlation maps. This review also presents some applications of these sequences in plant science.
Highlights
The fast and non-invasive methods to determine oil content in oilseeds were the first applications of time domain nuclear magnetic resonance (TD–NMR) in plant science, and they have since been used in germplasm evaluation and plant breeding programs [1]
Most TD–NMR studies in plants are based on the measurement of T2 relaxation time obtained by the CPMG pulse sequence, which consists of a π/2 pulse in the x axis followed obtained by the CPMG pulse sequence, which consists of a π/2 pulse in the x axis folby time (τ) and a train of refocusing π pulses in the y axis separated by time 2τ (Figure 1 lowed by time (τ) and a train of refocusing π pulses in the y axis separated by time 2τ using θ = π ) [5]
The magnitude of the continuous wave free precession (CWFP) signal (|Mss|) is constant (dashed red line on top of the constructive (B) or destructive (C), depending on the precession angle ψ = $0 Tp ($0 is the CWFP signal in Figure 6B) and for ψ = (2n+1)π, it is dependent on M0, T1, and T2 according frequency offset from resonance), flip angle θ, and T1 and T2 relaxation times according to Equation (2)
Summary
The fast and non-invasive methods to determine oil content in oilseeds were the first applications of time domain nuclear magnetic resonance (TD–NMR) in plant science, and they have since been used in germplasm evaluation and plant breeding programs [1]. The analyses of oilseeds, with low moisture content, are performed by measuring the intensity of free induction decay (FID) after a radiofrequency (rf) pulse. Pulse sequences to measure longitudinal (T1 ) and transverse (T2 ) relaxation times, the self-diffusion coefficient (D), and flow [3] have been used in plant science for approximately four decades. In the lasts two decades, one-dimensional (1D) and two-dimension (2D) pulses sequences have been proposed for TD–NMR [3,12,13,14,15]. This mini-review focuses on sequences, such as CPMG with low refocusing pulses, which minimize the sample-heating. 22of of problem, 2D2D sequences based on aon special regime of steady state free precession, problem,and and1D
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