Hypericin and pseudohypericin concentrations of a valuable medicinal plant Hypericum perforatum L. are enhanced by arbuscular mycorrhizal fungi

Hypericum perforatum L. (St. John’s-wort, Hypericaceae) is a valuable medicinal plant species cultivated for pharmaceutical purposes. Although the chemical composition and pharmacological activities of H. perforatum have been well studied, no data are available concerning the influence of arbuscular mycorrhizal fungi (AMF) on this important herb. A laboratory experiment was therefore conducted in order to test three AMF inocula on H. perforatum with a view to show whether AMF could influence plant vitality (biomass and photosynthetic activity) and the production of the most valuable secondary metabolites, namely anthraquinone derivatives (hypericin and pseudohypericin) as well as the prenylated phloroglucinol—hyperforin. The following treatments were prepared: (1) control—sterile soil without AMF inoculation, (2) Rhizophagus intraradices (syn. Glomus intraradices), (3) Funneliformis mosseae (syn. Glomus mosseae), and (4) an AMF Mix which contained: Funneliformis constrictum (syn. Glomus constrictum), Funneliformis geosporum (syn. Glomus geosporum), F. mosseae, and R. intraradices. The application of R. intraradices inoculum resulted in the highest mycorrhizal colonization, whereas the lowest values of mycorrhizal parameters were detected in the AMF Mix. There were no statistically significant differences in H. perforatum shoot mass in any of the treatments. However, we found AMF species specificity in the stimulation of H. perforatum photosynthetic activity and the production of secondary metabolites. Inoculation with the AMF Mix resulted in higher photosynthetic performance index (PItotal) values in comparison to all the other treatments. The plants inoculated with R. intraradices and the AMF Mix were characterized by a higher concentration of hypericin and pseudohypericin in the shoots. However, no differences in the content of these metabolites were detected after the application of F. mosseae. In the case of hyperforin, no significant differences were found between the control plants and those inoculated with any of the AMF applied. The enhanced content of anthraquinone derivatives and, at the same time, better plant vitality suggest that the improved production of these metabolites was a result of the positive effect of the applied AMF strains on H. perforatum. This could be due to improved mineral nutrition or to AMF-induced changes in the phytohormonal balance. Our results are promising from the biotechnological point of view, i.e. the future inoculation of H. perforatum with AMF in order to improve the quality of medicinal plant raw material obtained from cultivation

Drought-induced modifications of photosynthetic electron transport in intact leaves: Analysis and use of neural networks as a tool for a rapid non-invasive estimation

AbstractWater deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, QA–, is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of “unknown” samples with a correlation between calculated and gravimetrically determined RWC values of about R2≈0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Quenching of excited chlorophyll A in vivo by nitrobenzene.

Nitrobenzene exerts a dual effect on the excitation of chlorophyll a(Chl a) in vivo. (a) A 3(3,4-dichlorophenyl)-1,1-dimethylurea-inhibited quenching that manifests as a partial inhibition of variable chloroplast fluorescence and of 2,6-dichlorophenol indophenol (DCPIP) photoreduction and saturates at ca. 5-10 muM. Since nitrobenzene is not a Hill oxidant, this effect is attributed to a catalyzed back flow of electrons from intersystem intermediates to pre-photosystem II oxidants. (b) A direct quenching of the excited Chl a in vivo. This effect has a threshold of ca. 100 muM nitrobenzene; at higher concentrations it leads to almost complete suppression of chloroplast fluorescence and DCPIP photoreduction. Tris-washed chloroplast enriched in the photosystem II reaction center species Z+Q- and ZQ- are nearly four times more sensitive to nitrobenzene quenching than those enriched in Z+Q. On the other hand, normal chloroplasts are about 10 to the fourth times more sensitive. Hence, it is argued that the extreme sensitivity of normal chloroplast fluorescence is not due to a preferential association of nitrobenzene with a particular redox species of the reaction center