Resurrection Plants-A Valuable Source of Natural Bioactive Compounds: From Word-of-Mouth to Scientifically Proven Sustainable Use.

Resurrection plant species are a group of higher plants whose vegetative tissues are able to withstand long periods of almost full desiccation and recover quickly upon rewatering. Apart from being a model system for studying desiccation tolerance, resurrection plant species appear to be a valuable source of metabolites, with various areas of application. A significant number of papers have been published in recent years with respect to the extraction and application of bioactive compounds from higher resurrection plant species in various test systems. Promising results have been obtained with respect to antioxidative and antiaging effects in various test systems, particularly regarding valuable anticancer effects in human cell lines. Here, we review the latest advances in the field and propose potential mechanisms of action of myconoside-a predominant secondary compound in the European members of the Gesneriaceae family. In addition, we shed light on the possibilities for the sustainable use of natural products derived from resurrection plants.

Chemical Profiling, Antiproliferative and Antimigratory Capacity of Haberlea rhodopensis Extracts in an In Vitro Platform of Various Human Cancer Cell Lines.

Haberlea rhodopensis is a Balkan endemic plant that belongs to the Gesneriaceae family, and is believed to have medicinal use and health-promoting properties. This study aimed to (i) prepare aqueous (HAE) and ethanolic (HEE) extracts from the leaves of H. rhodopensis from in vitro propagated plants, (ii) screen for their potential antiproliferative and antimigratory activities, and (iii) chemically characterize both HAE and HEE by identifying compounds which may contribute to their observed bioactivity thereby further supporting their potential use in biomedical applications. The antiproliferative activity of both extracts was assessed against six human cancer cell lines by employing the sulforhodamine-B (SRB) assay. HEE was found to be more potent in inhibiting cancer cell growth as compared to HAE. Therefore, HEE's antimigratory effects were further studied in hepatocellular carcinoma (HepG2) and non-small cell lung adenocarcinoma (A459) cell lines as they were among the most sensitive ones to its antiproliferative activity. HEE was found to exert significant antimigratory concentration-dependent effects in both cell lines assessed with the wound healing assay. Chemical characterization by UPLC-MS/MS analysis identified that HEE contains higher levels of flavonoids, phenolic compounds, pigments (chlorophyll-/-b, lycopene, and ß-carotene), monoterpenoids, and condensed tannins compared to HAE, while HAE, contains higher levels of soluble protein and sugars. Furthermore, HEE demonstrated remarkable antioxidant activity evaluated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH●), 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS●+) and ferric reducing/antioxidant power (FRAP) assays. We have obtained comprehensive results highlighting the potential of HEE as a source of bioactive compounds with anticancer properties. Future studies should aim at identifying the chemical constituents responsible for the bioactivities observed, and focus on investigating HEE's effects, in in vivo preclinical cancer models.

Myconoside interacts with the plasma membranes and the actin cytoskeleton and provokes cytotoxicity in human lung adenocarcinoma A549 cells.

Studies have been carried out on the effects of the phenyl glycoside myconoside, extracted from the relict, Balkan endemic resurrection plant Haberlea rhodopensis on the plasma membrane structural organization and the actin cytoskeleton. Because the plasma membrane is the first target of exogenous bioactive compounds, we focused our attention on the influence of myconoside on the membrane lipid order and actin cytoskeleton in human lung adenocarcinoma A549 cells, using fluorescent spectroscopy and microscopy techniques. We found that low myconoside concentration (5 µg/ml) did not change cell viability but was able to increase plasma membrane lipid order of the treated cells. Higher myconoside concentration (20 µg/ml) inhibited cell viability by decreasing plasma membrane lipid order and impairing actin cytoskeleton. We hypothesize that the observed changes in the plasma membrane structural organization and the actin cytoskeleton are functionally connected to cell viability. Biomimetic membranes were used to demonstrate that myconoside is able to reorganize the membrane lipids by changing the fraction of sphingomyelin-cholesterol enriched domains. Thus, we propose a putative mechanism of action of myconoside on A549 cells plasma membrane lipids as well as on actin filaments in order to explain its cytotoxic effect at high myconoside concentration.

In vivo spectroscopy and NMR metabolite fingerprinting approaches to connect the dynamics of photosynthetic and metabolic phenotypes in resurrection plant Haberlea rhodopensis during desiccation and recovery.

The resurrection plant Haberlea rhodopensis was used to study dynamics of drought response of photosynthetic machinery parallel with changes in primary metabolism. A relation between leaf water content and photosynthetic performance was established, enabling us to perform a non-destructive evaluation of the plant water status during stress. Spectroscopic analysis of photosynthesis indicated that, at variance with linear electron flow (LEF) involving photosystem (PS) I and II, cyclic electron flow around PSI remains active till almost full dry state at the expense of the LEF, due to the changed protein organization of photosynthetic apparatus. We suggest that, this activity could have a photoprotective role and prevent a complete drop in adenosine triphosphate (ATP), in the absence of LEF, to fuel specific energy-dependent processes necessary for the survival of the plant, during the late states of desiccation. The NMR fingerprint shows the significant metabolic changes in several pathways. Due to the declining of LEF accompanied by biosynthetic reactions during desiccation, a reduction of the ATP pool during drought was observed, which was fully and quickly recovered after plants rehydration. We found a decline of valine accompanied by lipid degradation during stress, likely to provide alternative carbon sources for sucrose accumulation at late stages of desiccation. This accumulation, as well as the increased levels of glycerophosphodiesters during drought stress could provide osmoprotection to the cells.

Surface electric charge of thylakoid membranes from genetically modified tobacco plants under freezing stress.

In the present study we characterize for the first time electrokinetic and light scattering properties of thylakoids from freezing-tolerant tobacco plants, transformed to accumulate osmoprotectants (proline: AtP5Cs, VacP5Cs; fructan: SacB; glycine betaine: codA). Tobacco plants of wild type (WT) and transformed variants were cultivated at 2°C (cold acclimated) and -2°C (freezing stressed). "Lower salt" thylakoids (I=0.0006) of WT and SacB plants exhibited a decrease in electrophoretic mobility (EPM) after (2°C) treatment. AtP5Cs thylakoids (22°C) show a substantial increase in negative electrical charge (σ) upon illumination. We observed that "low salt"SacB thylakoids at 22°C and 2°C increased the σ on their membrane surfaces during the process of acclimation. WT (22°C) and AtP5Cs thylakoids (2°C) in "low salt" media (I=0.0156) showed a substantial increase in surface electrical charge upon illumination. Cold acclimation on WT and freezing stress on transformed plants resulted in a decrease in aggregation of thylakoids at both ionic strengths. There was a large enhancement in the relaxation capacity of reverse photosynthetic reactions in codA and SacB tobacco after freezing stress. Maximal intensity of the delayed light emission following low temperature stimuli was decreased, revealing a path for tobacco transformants to improve their cold stress tolerance. Here, we suggest the EPM value as an indicator for stability of thylakoids undergone genetic transformation.