Component Composition of Tonoplast Sterol Fractions under Conditions of Stress Caused by Copper Ions

Abstract

The influence of toxic concentrations of copper ions (100 and 500 μM) on the composition of sterols in the vacuolar membrane of beet roots was studied (Beta vulgaris L.). As a result of the studies, 12 compounds were identified in the free sterol (FS) fraction and 11 compounds in the sterol ester (ES) fraction. The ES contained compounds that were not found in the FS. Interestingly, the total content of these biologically active compounds increased at 500 µM Cu²⁺. A decrease in such triterpenes as lanosta-7,9(11)-diene-3β,18,20-triol, 3,18-diacetate, (20R)-(C₃₄N₅₄O₅) was observed in FS and ES. In the FS fraction, the content of the compound 7,8-epoxylanostan-11-ol, 3-acetoxy- increased under stress, while its amount decreased in the ES. It has been established that the total content ∆5-sterols, under normal conditions and under stress, amounted to no more than 33% in the fraction of free sterols and 21% in the fraction of sterol esters. The predominant sterol was β-sitosterol. Its content decreased under the stress conditions studied in both sterol fractions. The results obtained show that the fractions of tonoplast sterols (FS and ES) are represented not only by ∆5-sterols, which are mainly studied in works devoted to membranology and lipidology of plants, but also by triterpene compounds and other substances with biological activity. The discovered substances may possibly affect the biophysical parameters of the tonoplast and the metabolic processes of the cell in which the vacuolar membrane is involved. The identified compounds actively responded to the toxic effects of Cu²⁺ ions, which can be considered as one of the mechanisms for protecting the plant cell from stress.