Histochemistry and cell wall specialization of oil cells related to the essential oil accumulation in the bark of Cinnamomum cassia Presl. (Lauraceae)

Abstract

Chinese cinnamon (Cinnamomum cassia) has economic value as an aromatic and medicinal plant, and its bark oil has a very high trans-cinnamaldehyde content. To gain insight into the accumulation of bark oil and the biological mechanisms which permit the accumulation of a high level of aldehydes in C. cassia bark, the morphology and histochemistry of oil cells and the specialization in its walls were assessed by light and fluorescence microscopy. The histochemical tests localized in situ the main chemical classes of metabolites in oil cells, which included aldehydes, lipids and terpenoids. In oil cells the aldehydes distributed in the area surrounding the oil sac were compartmentalized from lipid compounds in the center; the oil sac in an oil cell was attached by multiple cupules rather than one cupule. The autofluorescence of oil-cell walls was attributed to the presence of suberin and lignin, and was confirmed by different methods. The lignified and suberized walls probably serve as protective barriers against the cytotoxicity of high contents of trans-cinnamaldehyde to the surrounding active cells. These results contribute to our knowledge of the structure of oil cells and accumulation of essential oil in Chinese cinnamon bark.