Raman spectroscopy: a tool for the characterization of plant mineral deposits

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Kontoyannis, Christos
Orkoula, Malvina
Karabourniotis, Georgios
Katri, Magda
Dimitrakopoulou, Aikaterini
Lourida, Vasiliki
Nikolopoulos, Dimosthenis
Tooulakou, Georgia
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Calcium salts of oxalate and carbonate are common crystalline mineral deposits in plant tissues. Calcium oxalate occurs in the vacuoles of specialized idioblastic cells (crystal cells) while calcium carbonate usually forms amorphous deposits called cystoliths. Characterization of the substances present in a crystal cell or in a lithocyst is an important step in deciphering the metabolic interactions between these mineral deposits and the plant cells. Different methods have been used for their characterization including scanning electron microscopy techniques, powder diffraction X-ray analysis, X-ray absorption spectroscopy, and infrared spectroscopy. Application of the above-mentioned techniques is usually complicated and destructive for the specimen. In the present work, Raman spectroscopy, a non-destructive vibrational technique, was applied on cystoliths that were isolated from Morus alba leaves and crystals isolated from Amaranthus hybridus. It was found that the cystoliths from Morus contained mainly calcium carbonate while the crystals from Amaranthus were made almost exclusively of calcium oxalate monohydrate. Differences in the Raman spectra were observed during leaf development, indicating that Raman spectroscopy can be a valuable tool in the search for the role of cystoliths.
Cystoliths, Calcium oxalate, Raman spectroscopy, Calcium carbonate