College of Agriculture & Biotechnology/Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology/The State Agriculture Ministry Laboratory of Horticultural Plant Growth, Development and Quality Improvement, Zhejiang University, Zijingang Campus, Hangzhou 310058, China.
State Key Laboratory of Surface Physics and Department of Physics, Human Phenome Institute, Multiscale Research Institute of Complex Systems, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China.
Cells. 2020 Mar 20;9(3):761. doi: 10.3390/cells9030761.
Softening of fruit during the postharvest storage, which is mainly associated with both compositional and spatial changes of polysaccharides within cell wall, affects the texture and quality of fruit. Current research on the fruit softening mechanism lacks an understanding of the overall softening at the cell level. The objective of this work was to investigate the change in the spatial distribution of cell wall polysaccharides in peach flesh cells at both single- and multiple-cell levels in a label-free way during the postharvest storage. Nonmelting peaches ( L. Batsch cv."Zhonghuashoutao") at commercial maturity were stored at 0 °C and 20 °C. Firmness measurement and chemical analysis were performed at each storage time. In addition, three molecular imaging techniques, namely confocal Raman microspectroscopy (CRM), Fourier transform infrared microspectroscopy (FTIRM), and stimulated Raman scattering microscopy (SRS) were used to visualize changes in the spatial distribution of cell wall polysaccharides of peach fruit in a label-free way during the postharvest storage. The combination of CRM and FTIRM provided complementary spectral information to visualize the spatial changes of cellulose, hemicellulose, and pectin in the cell wall of peach flesh during softening at the single-cell level, and found that the cell wall polysaccharides tended to be concentrated in the cell corner of parenchymal cells at the late stage. Furthermore, SRS, which is an ultrafast Raman imaging technique (approximately three or four orders of magnitude faster than CRM), was used for high-throughput cell wall phenotypes measurement. Different degradation degrees of parenchymal cells during fruit softening were found based on the gray-scale statistical analysis of SRS data. In general, cell wall polysaccharides decreased during softening and tended to be concentrated in the cell corner for most parenchymal cells at the late stage, but there were also some cells not in line with the whole softening trends. The results show that there were differences in the content and spatial changes of cell wall polysaccharides among parenchymal cells of peach fruit during the softening process, and the hybrid use of CRM, FTIRM, and SRS is a promising method for simultaneous visualization of changes in cell wall polysaccharides of peach.
果实采后贮藏过程中的软化主要与细胞壁多糖的组成和空间变化有关，会影响果实的质地和品质。目前对果实软化机制的研究缺乏对细胞水平整体软化的认识。本工作旨在以非破坏性方式研究桃果肉细胞在单个和多个细胞水平上细胞壁多糖在采后贮藏过程中的空间分布变化。将商业成熟的非融解桃（L. Batsch cv."Zhonghuashoutao"）在 0°C 和 20°C 下贮藏。在每个贮藏时间点进行硬度测量和化学分析。此外，使用三种分子成像技术，即共聚焦拉曼显微镜（CRM）、傅里叶变换红外显微镜（FTIRM）和受激拉曼散射显微镜（SRS），以非破坏性方式可视化桃果实细胞壁多糖在采后贮藏过程中的空间分布变化。CRM 和 FTIRM 的结合提供了互补的光谱信息，可在单细胞水平上可视化软化过程中细胞壁中纤维素、半纤维素和果胶的空间变化，并发现细胞壁多糖在果肉细胞的细胞角处趋于集中。此外，SRS（一种超快拉曼成像技术，比 CRM 快约三个或四个数量级）用于高通量细胞壁表型测量。根据 SRS 数据的灰度统计分析，发现了果实软化过程中不同程度的质体细胞降解。总的来说，细胞壁多糖在软化过程中减少，并在后期趋于在大多数质体细胞的细胞角处集中，但也有一些细胞不符合整体软化趋势。结果表明，在软化过程中，桃果肉质体细胞的细胞壁多糖含量和空间变化存在差异，CRM、FTIRM 和 SRS 的混合使用是一种同时可视化桃细胞壁多糖变化的有前途的方法。
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