Direct evidence for dynamics of cell heterogeneity in watercored apples: turgor-associated metabolic modifications and within-fruit water potential gradient unveiled by single-cell analyses

Abstract

Watercore is a physiological disorder in apple (Malus × domestica Borkh.) fruits that appears as water-soaked tissues adjacent to the vascular core, although there is little information on what exactly occurs at cell level in the watercored apples, particularly from the viewpoint of cell water relations. By combining picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS) with freezing point osmometry and vapor pressure osmometry, changes in cell water status and metabolisms were spatially assayed in the same fruit. In the watercored fruit, total soluble solid was lower in the watercore region than the normal outer parenchyma region, but there was no spatial difference in the osmotic potentials determined with freezing point osmometry. Importantly, a disagreement between the osmotic potentials determined with two methods has been observed in the watercore region, indicating the presence of significant volatile compounds in the cellular fluids collected. In the watercored fruit, cell turgor varied across flesh, and a steeper water potential gradient has been established from the normal outer parenchyma region to the watercore region, retaining the potential to transport water to the watercore region. Site-specific analysis using picoPPESI-MS revealed that together with a reduction in turgor, remarkable metabolic modifications through fermentation have occurred at the border, inducing greater production of watercore-related volatile compounds, such as alcohols and esters, compared with other regions. Because alcohols including ethanol have low reflection coefficients, it is very likely that these molecules would have rapidly penetrated membranes to accumulate in apoplast to fill. In addition to the water potential gradient detected here, this would physically contribute to the appearance with high tissue transparency and changes in colour differences. Therefore, it is concluded that these spatial changes in cell water relations are closely associated with watercore symptoms as well as with metabolic alterations.

Dynamics and stabilization mechanism of mitochondrial cristae morphofunction associated with turgor-driven cardiolipin biosynthesis under salt stress conditions

“…By adopting an ESI–MS emitter electrode embedded in the microfabricated capillary tip used for CPP filled with silicone + ionic solution 25 , it is noteworthy that the system is capable of determining numerous cell metabolites after knowing the water status of the cells, where the tip was impaled. The robustness of picoPPESI-MS has been demonstrated in the snap-shot analysis in various plant cells 25 , 27 , 28 , 31 , 56 , but not for time-course analysis. Retaining the function of a CPP, the method can be applied to the cells attached to the plants to avoid possible artifacts that might occur at tissue preparation including cutting.…”

“…It was shown that picoPPESI-MS was capable for discriminating metabolites between the neighboring cells 25 , 26 as well as at single rice pollen grains enclosed in the growing anthers in the attached plants 27 . As shown previously 28 , this approach also allows real-time investigation of the inherent heterogeneity in single-cells, providing in-situ biological information including the cell water status that had never been attainable in the past. Moreover, using a ‘transparent’ microcapillary allows to determine the volume of fluids by the mean of pressure control.…”

“…In picoPPESI-MS, cell sap collection can be completed within 0.5 s, quicker than the half time (typically, > 2 s) for water permeability in plant cells 29 , 30 , implying that potential dilution and contamination effects caused by water and/or solute movements between the impaled cells and neighboring cells might be negligible. While a snap-shot picoPPESI-MS analysis has been succeeded in various plant cells 25 – 28 , 31 , no attempt has been made for the time-course picoPPESI-MS analysis coupled with the volume determination.…”

Applications of ambient ionization mass spectrometry in 2021: An annual review

“…105 Finally, exploring the metabolome of plants and agricultural products can provide insight into factors affecting growth and quality. Picolitre pressure-probe electrospray-ionization MS (picoPPESI) MS has been used to study the effects of temperature on rice yield and quality, 106 in addition to, profiling apple metabolites 107 and DESI have been used to image plant hormones during development. 108 F I G U R E 3 Representative MasSpec Pen mass spectra from meat products, PCA plot differentiating samples, and image showing direct analysis of beef sample using the MasSpec Pen.…”

'Roly-poly toy' motion during pollen exudation promotes rapid pollen adhesion in rice

“…On-site chemical identi cation in the nanolitre uids exudated from plant organs has been hampered by the technical di culty in site-speci cally characterizing the molecules in the uids (or cellular uids) in real-time. Recent studies have shown the robustness of an on-site single-cell metabolomics, picolitre pressure-probe electrospray-ionisation mass spectrometry (picoPPESI-MS) 6 in various living plant cells 6,9,[25][26][27][28][29][30] . In this work, we revisit pollen exudation during rice pollination.…”