Spatial and temporal evolution of quantitative magnetic resonance imaging parameters of peach and apple fruit – relationship with biophysical and metabolic traits

Abstract

SUMMARYFruits are complex organs that are spatially regulated during development. Limited phenotyping capacity at cell and tissue levels is one of the main obstacles to our understanding of the coordinated regulation of the processes involved in fruit growth and quality. In this study, the spatial evolution of biophysical and metabolic traits of peach and apple fruit was investigated during fruit development. In parallel, the multi‐exponential relaxation times and apparent microporosity were assessed by quantitative magnetic resonance imaging (MRI). The aim was to identify the possible relationships between MRI parameters and variations in the structure and composition of fruit tissues during development so that transverse relaxation could be proposed as a biomarker for the assessment of the structural and functional evolution of fruit tissues during growth. The study provides species‐specific data on developmental and spatial variations in density, cell number and size distribution, insoluble and soluble compound accumulation and osmotic and water potential in the fruit mesocarp. Magnetic resonance imaging was able to capture tissue evolution and the development of pericarp heterogeneity by accessing information on cell expansion, water status and distribution at cell level, and microporosity. Changes in vacuole‐related transverse relaxation rates were mostly explained by cell/vacuole size. The impact of cell solute composition, microporosity and membrane permeability on relaxation times is also discussed. The results demonstrate the usefulness of MRI as a tool to phenotype fruits and to access important physiological data during development, including information on spatial variability.

MRI investigation of internal defects in potato tubers with particular attention to rust spots induced by water stress

“…The optimum adjustment of transverse relaxation curves was obtained using a bi-exponential model for the rust spots and for the healthy perimedullary regions, indicating that cell membranes acted, at least to some extent, as barriers to diffusive exchanges of water molecules between cell compartments. In both cases, two water pools with similar relative signal amplitudes were detected, probably corresponding to cytoplasm and vacuole compartments (Hills and Le Floc'h, 1994) or to the vacuoles of two cell populations with distinct volume distributions, as has been observed in peaches (Musse et al, 2021). Both T2s of the bi-exponential relaxation signal were higher in the rust spots than the healthy tissues.…”

“…Based on longitudinal (T1) and transverse (T2) NMR relaxation times, the contrast in MRI images can be adjusted to give a visual image of the internal structure of plant organs. Besides its great potential for the morphological study of fruit and vegetables, MRI is also highly relevant for the evaluation of microstructural changes at the cellular level (Musse et al, 2021;Van As, 2007). In fact, T1 and T2 of water are sensitive to metabolites content (sugar, starch, etc.…”

Sensors and Instruments for Brix Measurement: A Review

“…They could relate the soluble solids content of pomegranate with Spin–spin relaxation time, T2, measured using a low magnetic field (0.04 T). Similarly, a detailed study of biophysical, histological, and metabolic traits of fruit development was reported by Musse et al [ 69 ] with a dependable explanation of the changes in relaxation parameters. Hence, MRI can be used to provide information on cell expansion in a noninvasive manner.…”

Quantitative MRI analysis of structural changes in tomato tissues resulting from dehydration

“…However, as stated above, it is important to note that the reasoning applied can only be an approximation as the pericarp did not consist only of large cells and because their relative size appears to be affected by drying. In order to elucidate this further, the results of the present study were compared with the relaxation time measurements in apple and peach fruit [ 14 ] under very similar experimental conditions (using the same B 0 and TE), by setting the diameter of the cell tomato parenchyma at 280 μm, in line with the value reported in Legland et al [ 31 ] Here, the T 23 values measured in fresh and dried tomato pericarps (Regime 1‐A, 727 and 526 ms, respectively) are consistent with the variations expected from the relationship between 3/R and 1/T 2 , with R‐radius, from Musse et al [ 14 ] This shows that, although the variation in cell size is not the only mechanism that could explain the T 2 variations, cell size seems to have a dominant impact on T 2 values for tissues with little porosity.…”