Phytohormone Priming: Regulator for Heavy Metal Stress in Plants

Phytohormones act as chemical messengers and, under a complex regulation, allow plants to sustain biotic and abiotic stresses. Thus, phytohormones are known for their regulatory role in plant growth and development. Heavy metals (HMs) play an important role in metabolism and have roles in plant growth and development as micronutrients. However, at a level above threshold, these HMs act as contaminants and pose a worldwide environmental threat. Thus, finding eco-friendly and economical deliverables to tackle this problem is a priority. In addition to physicochemical methods, exogenous application of phytohormones, i.e., auxins, cytokinins, and gibberellins, can positively influence the regulation of the ascorbate–glutathione cycle, transpiration rate, cell division, and the activities of nitrogen metabolism and assimilation, which improve plant growth activity. Brassinosteroids, ethylene and salicylic acid have been reported to enhance the level of the anti-oxidant system, decrease levels of ROS, lipid peroxidation and improve photosynthesis in plants, when applied exogenously under a HM effect. There is a crosstalk between phytohormones which is activated upon exogenous application. Research suggests that plants are primed by phytohormones for stress tolerance. Chemical priming has provided good results in plant physiology and stress adaptation, and phytohormone priming is underway. We have reviewed promising phytohormones, which can potentially confer enhanced tolerance when used exogenously. Exogenous application of phytohormones may increase plant performance under HM stress and can be used for agro-ecological benefits under environmental conditions with high HMs level.

     

Heavy metal-induced oxidative damage, defense reactions, and detoxification mechanisms in plants

Heavy metal (HMs) contamination is widespread globally due to anthropogenic, technogenic, and geogenic activities. The HMs exposure could lead to multiple toxic effects in plants by inducing reactive oxygen species (ROS), which inhibit most cellular processes at various levels of metabolism. ROS being highly unstable could play dual role (1) damaging cellular components and (2) act as an important secondary messenger for inducing plant defense system. Cells are equipped with enzymatic and non-enzymatic defense mechanisms to counteract this damage. Some are constitutive and others that are activated only when a stress-specific signal is perceived. Enzymatic scavengers of ROS include superoxide dismutase, catalase, glutathione reductase, and peroxidase, while non-enzymatic antioxidants are glutathione, ascorbic acid, α-tocopherol, flavonoids, anthocyanins, carotenoids, and organic acids. The intracellular and extracellular chelation mechanisms of HMs are associated with organic acids such as citric, malic and oxalic acid, etc. The important mechanism of detoxification includes metal complexation with glutathione, amino acids, synthesis of phytochelatins and sequestration into the vacuoles. Excessive stresses induce a cascade, MAPK (mitogen-activated protein kinase) pathway and synthesis of metal-detoxifying ligands. Metal detoxification through MAPK cascade and synthesis of metal-detoxifying ligands will be of considerable interest in the field of plant biotechnology. Further, the photoprotective roles of pigments of xanthophylls cycle under HMs stress were also discussed.     

Lettuce flavonoids screening and phenotyping by chlorophyll fluorescence excitation ratio

Main conclusion

Environmentally induced variation and the genotypic differences in flavonoid and phenolic content in lettuce can be reliably detected using the appropriate parameters derived from the records of rapid non-invasive fluorescence technique.

The chlorophyll fluorescence excitation ratio method was designed as a rapid and non-invasive tool to estimate the content of UV-absorbing phenolic compounds in plants. Using this technique, we have assessed the dynamics of accumulation of flavonoids related to developmental changes and environmental effects. Moreover, we have tested appropriateness of the method to identify the genotypic differences and fluctuations in total phenolics and flavonoid content in lettuce. Six green and two red genotypes of lettuce (Lactuca sativa L.) grown in pots were exposed to two different environments for 50 days: direct sunlight (UV-exposed) and greenhouse conditions (low UV). The indices based on the measurements of chlorophyll fluorescence after red, green and UV excitation indicated increase of the content of UV-absorbing compounds and anthocyanins in the epidermis of lettuce leaves. In similar, the biochemical analyses performed at the end of the experiment confirmed significantly higher total phenolic and flavonoid content in lettuce plants exposed to direct sun compared to greenhouse conditions and in red compared to green genotypes. As the correlation between the standard fluorescence indices and the biochemical records was negatively influenced by the presence of red genotypes, we proposed the use of a new parameter named Modified Flavonoid Index (MFI) taking into an account both absorbance changes due to flavonol and anthocyanin content, for which the correlation with flavonoid and phenolic content was relatively good. Thus, our results confirmed that the fluorescence excitation ratio method is useful for identifying the major differences in phenolic and flavonoid content in lettuce plants and it can be used for high-throughput pre-screening and phenotyping of leafy vegetables in research and breeding applications towards improvement of vegetable health effects.

     

Effect of chlorocholine chlorid on phenolic acids accumulation and polyphenols formation of buckwheat plants

Background

Effect of chlorocholine chloride (CCC) on phenolic acids composition and polyphenols accumulation in various anatomical parts (stems, leaves and inflorescences) of common buckwheat (Fagopyrum esculentum Moench) in the early stages of vegetation period were surveyed.

Results

Treatment of buckwheat seeds with 2% of CCC has been increased content of total phenolics in the stems, leaves and inflorescences. On analyzing the different parts of buckwheat plants, 9 different phenolic acids – vanilic acid, ferulic acid, trans-ferulic acid, chlorogenic acid, salycilic acid, cinamic acid, p-coumaric acid, p-anisic acid, methoxycinamic acid and catechins were identified. The levels of identified phenolic acids varied not only significantly among the plant organs but also between early stages of vegetation period. Same changes as in contents of chlorogenic acid, ferulic acid, trans-ferulic acid were found for content of salycilic acid. The content of these phenolic acids has been significant increased under effect of 2% CCC treatment at the phase I (formation of buds) in the stems and at the phase II (beginning of flowering) in the leaves and then inflorescences respectively. The content of catechins as potential buckwheat antioxidants has been increased at the early stages of vegetation period after treatment with 2% CCC.

Conclusions

The obtained results suggest that influence of CCC on the phenolics composition can be a result of various mechanisms of CCC uptake, transforming and/or its translocation in the buckwheat seedlings.     

The application of multiplex fluorimetric sensor for the analysis of flavonoids content in the medicinal herbs family Asteraceae,Lamiaceae, Rosaceae

Background

The aim of our research work was to quantify total flavonoid contents in the leaves of 13 plant species family Asteraceae, 8 representatives of family Lamiaceae and 9 plant species belonging to family Rosaceae, using the multiplex fluorimetric sensor. Fluorescence was measured using optical fluorescence apparatus Multiplex(R) 3 (Force-A, France) for non-destructive flavonoids estimation. The content of total flavonoids was estimated by FLAV index (expressed in relative units), that is deduced from flavonoids UV absorbing properties.

Results

Among observed plant species, the highest amount of total flavonoids has been found in leaves of Helianthus multiflorus (1.65 RU) and Echinops ritro (1.27 RU), Rudbeckia fulgida (1.13 RU) belonging to the family Asteraceae. Lowest flavonoid content has been observed in the leaves of marigold (Calendula officinalis) (0.14 RU) also belonging to family Asteraceae. The highest content of flavonoids among experimental plants of family Rosaceae has been estimated in the leaves of Rosa canina (1.18 RU) and among plant species of family Lamiaceae in the leaves of Coleus blumei (0.90 RU).

Conclusions

This research work was done as pre-screening of flavonoids content in the leaves of plant species belonging to family Asteraceae, Lamiaceae and Rosaceae. Results indicated that statistically significant differences (P > 0.05) in flavonoids content were observed not only between families, but also among individual plant species within one family.     

Anatomical,Morphological, and Chemical Characterizations and Biological Activities of Gagea taurica Steven (Liliaceae): A New Record for the Turkish Flora

Gagea genus, which is native to the Mediterranean and Black Sea regions, has attracted significant attention due to its biodiversity and potential health benefits. In this study, the biochemical composition and biological activities of methanol extracts from various parts of G. taurica were investigated, along with their anatomical and morphological characteristics. The best antimicrobial activity was found to be MeOH extracts of corm and leaf against several Candida strains with MIC=640 μg/mL. The highest level of phenolics together with significant results of antioxidant activities were observed in flowers extracts. The α-amylase inhibition assay results showed that the highest inhibition percentage was observed with acarbose (59 %), followed by leaf extract (43 %). Leaf exhibited the most effective inhibitory activity in AChE inhibition assay, whereas flower demonstrated the most significant inhibitory activity in BChE inhibition assay. Hesperidin was found as 1621.0001 ng/ml value in flower extract and 283.9339 ng/ml value leaf.     

Comparative analysis of bioactive phenolic compounds composition from 26 medicinal plants

Bioactive phenolic compounds are powerful antioxidants in traditionally used medicinal and industrial crop plants and have attracted increased interest in the last years in their application and role in non-destructive methodology for pre-screening analysis of some stress factors. In this study the qualitative target was linked with future possible applications of received data for improving non-destructive methodology as well as for improving existing knowledge regarding antioxidant content in some plant species. Comparative analysis of total phenolics, flavonoid contents, phenolic acid composition, and antioxidant activity in known east central Europe medicinal and industrial crop plants of 26 species of families Asteraceae, Rosaceae and Lamiaceae was done. Among the investigated leaf extracts the highest total phenolic, total flavonoid contents and antioxidant activity have been seen for Stachys byzantine L. (Lamiaceae), Calendula officinalis L. (Asteraceae) and for Potentilla recta L. (Rosaceae). The highest syringic acid content has been found in the leaf extracts of plant family Asteraceae – in the range from 0.782 to 5.078 mg g^?1 DW. The representative’s family Rosaceae has a higher content of p-anisic acid in the range 0.334–3.442 mg g^?1DW compared to the leaf extracts of families Lamiaceae and Asteraceae. The comparative study showed significant differences of content of phenolic acids in the leaf extracts of different representative’s families Rosaceae, Asteraceae and Lamiaceae. We suggest that the presence of some phenolic acids can be used as a possible marker for family botanical specifications of representative families Asteraceae and Rosaceae. It was supposed that some pharmacological effects can be connected with the analyzed data.     

Low PSI content limits the photoprotection of PSI and PSII in early growth stages of chlorophyll b-deficient wheat mutant lines

Photosynthesis Research - In vivo analyses of electron and proton transport-related processes as well as photoprotective responses were carried out at different stages of growth in chlorophyll b...     

The anatomical,morphological features,and biological activity of Scilla siberica subsp. armena (Grossh.) Mordak (Asparagaceae)

Protoplasma - Scilla siberica subsp. armena is known as Siberian Squill which is naturally distributed in Lebanon-Syria, Transcaucasus, and Turkey. It is a perennial bulbous plant with a short...