Chemical Imaging of the Microstructure of Chickpea Seed Tissue within a Cellular Dimension Using Synchrotron Infrared Microspectroscopy: A Preliminary Study.

Synchrotron radiation-based infrared microspectroscopy (SR-IMS) is a nondestructive bioanalytical technique with a high signal-to-noise ratio and high ultraspatial resolution (3-10 μm). It is capable to explore the microstructures of plant tissues in a chemical sense and provide information on the composition, structure, and distribution of chemical compounds/functional groups. The objective of this study was to illustrate how SR-IMS can be used to image the internal microstructures of chickpea seed tissue within a cellular level. Chickpea seeds (CDC Cory) were collected from the Crop Development Center (University of Saskatchewan, Saskatoon, SK). The seeds were frozen at -20 °C on object disks in a cryostatic microtome and then were cut into thin cross sections (ca. 8 μm thick). The experiment was carried out on the mid-infrared beamline (01B1-1) at the Canadian Light Source (Saskatoon, SK). We obtained the ultraspatial images of the chickpea tissue with pixel-sized increments of imaging steps. The results showed that, with the extremely bright synchrotron light, spectra with high signal-to-noise ratios can be obtained from an area as small as 3.3 μm × 3.3 μm, allowing us to observe the seed tissue within a cellular level. Chemical distribution of chickpea such as lipids, protein, and carbohydrates could be mapped, revealing the chemical information of the chickpea internal microstructure. In conclusion, SR-IMS can rapidly characterize the molecular structure of protein, carbohydrates, and lipids at an ultraspatial resolution.