Defense potential of secondary metabolites in medicinal plants under UV-B stress

Integration of silicon and secondary metabolites in plants: a significant association in stress tolerance

As sessile organisms, plants are unable to avoid being subjected to environmental stresses that negatively affect their growth and productivity. Instead, they utilize various mechanisms at the morphological, physiological, and biochemical levels to alleviate the deleterious effects of such stresses. Amongst these, secondary metabolites produced by plants represent an important component of the defense system. Secondary metabolites, namely phenolics, terpenes, and nitrogen-containing compounds, have been extensively demonstrated to protect plants against multiple stresses, both biotic (herbivores and pathogenic microorganisms) and abiotic (e.g. drought, salinity, and heavy metals). The regulation of secondary metabolism by beneficial elements such as silicon (Si) is an important topic. Silicon-mediated alleviation of both biotic and abiotic stresses has been well documented in numerous plant species. Recently, many studies have demonstrated the involvement of Si in strengthening stress tolerance through the modulation of secondary metabolism. In this review, we discuss Si-mediated regulation of the synthesis, metabolism, and modification of secondary metabolites that lead to enhanced stress tolerance, with a focus on physiological, biochemical, and molecular aspects. Whilst mechanisms involved in Si-mediated regulation of pathogen resistance via secondary metabolism have been established in plants, they are largely unknown in the case of abiotic stresses, thus leaving an important gap in our current knowledge.

Climate change shapes the future evolution of plant metabolism

Planet Earth has experienced many dramatic atmospheric and climatic changes throughout its 4.5-billion-year history that have profoundly impacted the evolution of life as we know it. Photosynthetic organisms, and specifically plants, have played a paramount role in shaping the Earth's atmosphere through oxygen production and carbon sequestration. In turn, the diversity of plants has been shaped by historical atmospheric and climatic changes: plants rose to this challenge by evolving new developmental and metabolic traits. These adaptive traits help plants to thrive in diverse growth conditions, while benefiting humanity through the production of food, raw materials, and medicines. However, the current rapid rate of climate change caused by human activities presents unprecedented new challenges to the future of plants. Here, we discuss the potential effects of modern climate change on plants, with specific attention to plant specialized metabolism. We explore potential avenues of future scientific investigations, powered by cutting-edge methods such as synthetic biology and genome engineering, to better understand and mitigate the consequences of rapid climate change on plant fitness and plant usage by humans.

Simultaneous determination of 49 amino acids, B vitamins, flavonoids, and phenolic acids in commonly consumed vegetables by ultra-performance liquid chromatography-tandem mass spectrometry

A sensitive and reliable method was developed and validated for the simultaneous determination of 49 amino acids, B vitamins, flavonoids, and phenolic acids based on a rapid metabolomic extraction procedure combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in a single chromatographic run and applied in analysis of 26 commonly consumed vegetables. The chromatographic and sample preparation conditions were optimized, given the high diversity of the target analytes. Eight isotope-labeled standards were applied to validate the method in terms of recovery, linearity, matrix effects, precision, and sensitivity. Most recoveries in four vegetable matrices ranged from 65.0% to 105.3% with associated RSDs < 20%. Low LOQs ranged from 0.06 to 17 µg/kg. Linear calibration curves with different ranges were established with R² > 0.993. Among the 26 vegetables, purple cabbage, broccoli, and red lettuce were found to contain the highest concentrations of free amino acids, B vitamins, and phenolic compounds.

Current developments in the nanomediated delivery of photoprotective phytochemicals

Natural products have been used to protect the skin from harmful UV radiation for decades. Due to the ecotoxicological implications of synthetic sunscreen exposure in aquatic ecosystems, there is a greater need to explore alternative sources of UV filters. Recent research has focused on discovering novel UV absorbing photoprotective molecules from nature. In response to the excessive damage caused by UVB rays, plants induce the production of high concentrations of phytoprotective secondary metabolites and anti-oxidative enzymes. Despite promising UV absorbing and photoprotective properties, plant secondary metabolites have been underutilized in topical delivery due to low solubility and high instability. Numerous phytochemicals have been effectively nanosized, incorporated in formulations, and studied for their sustained effects in photoprotection. The present review outlines recent developments in nanosizing and delivering photoprotective crude plant extract and phytochemicals from a phytochemical perspective. We searched for articles using keywords: "UV damage," "skin photoprotection," "photodamage," and "nano delivery" in varied combinations. We identified and reviewed literature from 43 original research articles exploring nanosized phytochemicals and crude plant extracts with photoprotective activity. Nanosized phytochemicals retained higher amounts of bioactive compounds in the skin and acted as depots for their sustained release. Novel approaches in nanosizing considerably improved the photostability, efficacy, and water resistance of plant secondary metabolites. We further discuss the need for broad-spectrum sunscreen products, potential challenges, and future growth in this area.

Physiologic and Metabolic Changes in Crepidiastrum denticulatum According to Different Energy Levels of UV-B Radiation

Ultraviolet B (UV-B) light, as a physical elicitor, can promote the secondary metabolites biosynthesis in plants. We investigated effects of different energy levels of UV-B radiation on growth and bioactive compounds of Crepidiastrum denticulatum. Three-week-old seedlings were grown in a plant factory for 5 weeks. Plants were subjected to different levels of UV-B (0, 0.1, 0.25, 0.5, 1.0, and 1.25 W m⁻²), 6 h a day for 6 days. All UV-B treatments had no negative effect on the shoot dry weight; however, relatively high energy treatments (1.0 and 1.25 W m⁻²) inhibited the shoot fresh weight. UV-B light of 0.1, 0.25, and 0.5 W m⁻² did not affect total chlorophyll and H₂O₂ contents; however, they increased total carotenoid content. On 4 days, 0.25 W m⁻² treatment increased antioxidant capacity, total hydroxycinnamic acids (HCAs) content, and several sesquiterpenes. Treatments with 1.0 and 1.25 W m⁻² increased total carotenoid, total HCAs, and H₂O₂ contents, and destroyed chlorophyll pigments, reducing maximum quantum yield of photosystem II and causing visible damage to leaves. Partial least squares discrimination analysis (PLS-DA) showed that secondary metabolites were distinguishably changed according to energy levels of UV-B. The potential of 0.25 W m⁻² UV-B for the efficient production of bioactive compounds without growth inhibition in C. denticulatum was identified.

Food-derived bioactive compounds with anti-aging potential for nutricosmetic and cosmeceutical products

Besides providing essential nutrients for humans, food contains bioactive compounds that exert diverse biological activities such as anti-microbial, anti-cancerogenic, anti-viral, anti-inflammatory and antioxidant. The cosmetic industry is interested in natural bioactive compounds for their use in nutricosmetic and cosmeceutical products. These products aimed to reduce skin aging, inflammation or provide photoprotection against UV radiation. As a result, nutricosmetics and cosmeceuticals are becoming innovative self-care products in the beauty market. These products contain phytochemicals as active compounds obtained from fruits, vegetables, legumes, medicinal herbs and plants with anti-aging potential. This review summarizes the information within the last 5 years related to bioactive compounds present in fruits, vegetables, herbs and spices commonly used for human consumption. Their antioxidant and biological potential for modulating molecular markers involved in the aging process, as well as their mechanism of action. Diverse natural foods and their byproducts could be used as a source of bioactive compounds for developing cosmeceutical and nutricosmetic products.

Suppression of chorismate synthase, which is localized in chloroplasts and peroxisomes, results in abnormal flower development and anthocyanin reduction in petunia

In plants, the shikimate pathway generally occurs in plastids and leads to the biosynthesis of aromatic amino acids. Chorismate synthase (CS) catalyses the last step of the conversion of 5-enolpyruvylshikimate 3-phosphate (EPSP) to chorismate, but the role of CS in the metabolism of higher plants has not been reported. In this study, we found that PhCS, which is encoded by a single-copy gene in petunia (Petunia hybrida), contains N-terminal plastidic transit peptides and peroxisomal targeting signals. Green fluorescent protein (GFP) fusion protein assays revealed that PhCS was localized in chloroplasts and, unexpectedly, in peroxisomes. Petunia plants with reduced PhCS activity were generated through virus-induced gene silencing and further characterized. PhCS silencing resulted in reduced CS activity, severe growth retardation, abnormal flower and leaf development and reduced levels of folate and pigments, including chlorophylls, carotenoids and anthocyanins. A widely targeted metabolomics analysis showed that most primary and secondary metabolites were significantly changed in pTRV2-PhCS-treated corollas. Overall, the results revealed a clear connection between primary and specialized metabolism related to the shikimate pathway in petunia.

Active thermography for real time monitoring of UV-B plant interactions

Although Ultraviolet-B (UV-B)-plant interactions have been extensively analysed in the past years, many physiological aspects of the complex plant response mechanisms still need to be elucidated. Depending on the energy dose, this part of the electromagnetic spectrum can induce detrimental or beneficial effects in plant and fruit. In the present work, active thermography is used to analyse in real time the response of plants under different doses of artificial UV-B. In particular, we investigated the temporal variations of the leaf surface temperature (LST) to UV-B exposure by Long Pulse and Lock-in thermography in Epipremnum aureum and in Arabidopsis plants overexpressing or knockout mutants of UVR8, the known UV-B photoreceptor. In both cases, UV-B irradiation triggers a cooling effect, namely a thermal response characterised by a LST lower respect to the initial value. Lock-in thermography demonstrated that the cooling effect is associated with an immediate mobilization and accumulation of water in the leaves. Also, we demonstrated that thermographic responses change according to the different capability of plants to tolerate high UV-B radiation. Our study highlights new physiological and physical aspects of the plants response to UV-B radiation and, more in general, it opens new opportunities for the use of the thermography as smart tool for real-time monitoring of plant environmental interactions.

Effect on essential oil components and wedelolactone content of a medicinal plant Eclipta alba due to modifications in the growth and morphology under different exposures of ultraviolet-B

In the present study sensitivity of a medicinal plant Eclipta alba L. (Hassk) (False daisy) was assessed under intermittent (IT) and continuous (CT) doses of elevated ultraviolet-B (eUV-B). Eclipta alba is rich in medicinally important phytochemical constituents, used against several diseases. The hypothesis of this study is that alterations in UV-B dose may modify the quantity and quality of medicinally valuable components with changes in the morphological and physiological parameters of test plant. To fulfill our hypothesis IT and CT of eUV-B (ambient ± 7.2 kJ m^-2 day^-2) was given for 130 and 240 h respectively to assess the impact of UV-B stress. Growth and physiological parameters were adversely affected under both the treatments with varying magnitude. The observation of leaf surfaces showed increase in stomatal and trichome densities suggesting the adaptive resilience of the plants against UV-B. Besides, biosynthesis of wedelolactone, a major medicinal compound of E. alba was observed to be stimulated under UV-B exposure. The essential oil content was reduced under IT while increased under CT. A total of 114 compounds were identified from oil extract of E. alba. n-Pentadecane (25.79%), n-Octadecane (12.98%), β-Farnesene (9.43%), α-Humulene (4.95%) (E)-Caryophyllene (4.87%), Phytol (4.25%), α-Copaene (2.26%), Humulene epoxide (1.46%), β-Pinene (1.07) and β-Caryophyllene oxide (1.06%) were identified as major components of oil. CT induced the synthesis of some medicinally important compounds such as α-terpineol, δ-cadinene, linolenic acid, methyl linoleate and myristic acid amide. Hence, the study revealed that continuous UV-B exposure of low intensity could be helpful for commercial exploitation of essential oil in E. alba.

Transgenesis as a Tool for the Efficient Production of Selected Secondary Metabolites from in Vitro Plant Cultures

The plant kingdom abounds in countless species with potential medical uses. Many of them contain valuable secondary metabolites belonging to different classes and demonstrating anticancer, anti-inflammatory, antioxidant, antimicrobial or antidiabetic properties. Many of these metabolites, e.g., paclitaxel, vinblastine, betulinic acid, chlorogenic acid or ferrulic acid, have potential applications in medicine. Additionally, these compounds have many therapeutic and health-promoting properties. The growing demand for these plant secondary metabolites forces the use of new green biotechnology tools to create new, more productive in vitro transgenic plant cultures. These procedures have yielded many promising results, and transgenic cultures have been found to be safe, efficient and cost-effective sources of valuable secondary metabolites for medicine and industry. This review focuses on the use of various in vitro plant culture systems for the production of secondary metabolites.

Nitrogen in the defense system of Annona emarginata (Schltdl.) H. Rainer

The concentration of nitrogen can generate different strategies in plants in response to stress. In this study, we investigated how nitrogen concentration interferes with the defense system of Annona emarginata. Low concentrations of nitrogen increased the allocation of photosynthetic resources to carbon metabolism, resulting in an increase in the synthesis of volatile substances involved in signaling and defense that contributed to antioxidant enzymes in overcoming stress. The availability of nitrogen at 5.62 mM concentration might have helped to induce increased resistance in the plants because at this concentration, signaling substances and defense substances (monoterpenes and sesquiterpenes) were observed. Plants cultivated with the highest nitrate concentration displaced energy for the reduction of this ion, likely forming nitric oxide, a signaling molecule. This condition, together with the decrease in carbon skeletons, may have contributed to the lower synthesis of volatile substances of the specialized metabolism that are also involved with signaling. Varying the nitrogen in Annona emarginata cultivation revealed that depending on the concentration, volatile substances show higher or lower synthesis and participation in the system of signaling and defense in the plant. These results may suggest that volatile substances participate in resistance to pests and diseases, which is a necessary condition for Annona emarginata to be preferentially used as rootstock for Annona x atemoya.