The use of X-ray fluorescence analysis using synchrotron radiation to study the relationship between chemical elements and phenolic compounds in the blue honeysuckle plants
Presently studies of the role of trace and macro elements in the biogenesis of diverse biologically active phenolic compounds (PC) in medicinal plants have become increasingly actual due to PC great diversity and specific functions in physiological processes. Beneficial properties of blue honeysuckle Lonicera caerulea L. s.l. (Caprifoliaceae Juss.) are attributed to their PC pool, as well as to the trace and macro elements’ content. Earlier research carried out in the L. caerulea natural population on the Kurai Ridge of the Altai Mountains (Russia) revealed significant differences in PC content among the plants growing in similar environments. The aim of the study was to reveal the possible effect of soil elemental composition on trace and macro elements’ content and on the different PC classes in honeysuckle leaves. The soil and phytomass samples for analyses were collected in 4 sites of the L. caerulea population area in the Saryachik River valley on the Kurai Ridge of the Altai Mountains. The L. caerulea leaves were collected at the fruit ripening stage. The total content of trace and macro elements in soil and plants was determined by X-ray fluorescence analysis using synchrotron radiation (XRF SR) at the Elemental Analysis Station of the VEPP-3 storage ring at the Siberian Center for Synchrotron and Terahertz Radiation, Budker Institute of Nuclear Physics. Monochromatized synchrotron radiation with energy of 23 keV was used for fluorescence excitation. The irradiation time of each sample ranged from 150 to 400 s. Individual energy peaks corresponding to the measured elements and the peak area, which in turn corresponded to the concentrations of elements, were calculated for the resulting characteristic X-ray spectrum. Nineteen elements were identified in our studies (K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Rb, Sr, Zr, Nb, Mo, and Pb). The concentration of chemical elements in soil extracts was measured by atomic absorption. Chemical elements’ content in soils of the Saryachik River valley, as determined by XRF SR, showed considerable differences among blue honeysuckle habitats in the bulk contents of some macro (Ca, Fe) and trace (Ti, Mn, Sr, Zr, V, Zn, Rb, Ni, Cu, Pb, Co, As, Cr, Br and Mo) elements, as well as in labile forms of K, Ca, Fe, Mn, Sr, Zn, Ni, Cu, Pb and Co. Statistically significant correlation between bulk and labile forms of chemical elements was revealed only for Ca, Fe and Pb. Macro and trace elements’ content in honeysuckle leaves, as well as their physiologically informative ratios, also showed significant variation. Statistically significant correlation was found between hydroxycinnamic acids content and Cu, Rb, Mo and V in leaves, whereas decrease in K/Rb ratio in leaves was correlated with increased chlorogenic acid concentration. Significant increase in main PC classes was found in habitats with high soil Sr and Ca content, leading to decreased soil K/Ca ratio. The same habitats were characterized by increased Cu/Zn and Fe/Zn and decreased Fe/Cu и Fe/Ni raios. The obtained results suggest possible participation of biologically active polyphenols in regulating macro- and trace elements’ uptake by blue honeysuckle plants.