Metabolic profiling of Rhodiola rosea rhizomes by ¹H NMR spectroscopy.

INTRODUCTION: Rhodiola rosea is a broadly used medicinal plant with largely unexplored natural variability in secondary metabolite levels. OBJECTIVE: The aim of this work was to develop a non-target procedure for ¹H NMR spectroscopic fingerprinting of rhizome extracts for pattern recognition analysis and identification of secondary metabolites responsible for differences in sample composition. To achieve this, plants from three different geographic areas (Swiss Alps, Finland, and Altai region in Siberia) were investigated. RESULTS: A sample preparation procedure was developed in order to remove polymeric polyphenols as the ¹H NMR analysis of low-molecular-weight metabolites was hampered by the presence of tannins. Principal component analysis disclosed tight clustering of samples according to population. PCA models based on the aromatic region of the spectra showed that the first two components reflected changes in the content of salidroside and rosavin, respectively, the rosavin content being negatively correlated to that of rhodiocyanoside A and minor aromatics. Score plots and non-parametric variance tests demonstrated population-dependent changes according to harvest time. Data consistency was assessed using score plots and box-and-whisker graphs. In addition, a procedure for presenting loadings of PCA models based on bucketed data as high-resolution plots, which are reminiscent of real ¹H NMR spectra and help to identify latent biomarkers, is presented. CONCLUSION: This study demonstrated the usefulness of the established procedure for multivariate non-target ¹H NMR metabolic profiling of Rhodiola rosea.

NopL, an effector protein of Rhizobium sp. NGR234, thwarts activation of plant defense reactions.

Bacterial effector proteins delivered into eukaryotic cells via bacterial type III secretion systems are important virulence factors in plant-pathogen interactions. Type III secretion systems have been found in Rhizobium species that form symbiotic, nitrogen-fixing associations with legumes. One such bacterium, Rhizobium sp. NGR234, secretes a number of type III effectors, including nodulation outer protein L (NopL, formerly y4xL). Here, we show that expression of nopL in tobacco (Nicotiana tabacum) prevents full induction of pathogenesis-related (PR) defense proteins. Transgenic tobacco plants that express nopL and were infected with potato virus Y (necrotic strain 605) exhibited only very low levels of chitinase (class I) and beta-1,3-glucanase (classes I and III) proteins. Northern-blot analysis indicated that expression of nopL in plant cells suppresses transcription of PR genes. Treatment with ethylene counteracted the effect of NopL on chitinase (class I). Transgenic Lotus japonicus plants that expressed nopL exhibited delayed development and low chitinase levels. In vitro experiments showed that NopL is a substrate for plant protein kinases. Together, these data suggest that NopL, when delivered into the plant cell, modulates the activity of signal transduction pathways that culminate in activation of PR proteins.