UV-B Radiation as Abiotic Elicitor to Enhance Phytochemicals and Development of Red Cabbage Sprouts

Background: The main objective of this study was to evaluate the effect of periodical UV-B illumination during red cabbage germination on morphological development and the phenolics and carotenoid accumulation. Methods: During a sprouting period of 10 days at 20 °C in darkness, seedlings received 5, 10, or 15 kJ m−2 UV-B (T5, T10, and T15) applied in four steps (25% on days 3, 5, 7, and 10). UV untreated sprouts were used as control (CTRL). After 10 days of germination, the sprouts were harvested and stored 10 days at 4 °C as a minimally processed product. Phenolic and carotenoid compounds were analysed 1 h after each UV-B application and on days 0, 4, 7, and 10 during cold storage. Results: The longest hypocotyl length was observed in T10-treated sprouts. The total phenolic content (TPC), total flavonoid content (TFC), and total antioxidant capacity (TAC) increased during germination following a sigmoidal kinetic, especially in the UV-B-treated samples, which reported a dose-dependent behaviour. In this way, T10-treated sprouts increased the TPC by 40% after 10 days at 4 °C compared to CTRL, while TAC and TFC increased by 35 and 30%, respectively. Carotenoids were enhanced with higher UV-B doses (T15). Conclusions: We found that UV-B stimulated the biosynthesis of bioactive compounds, and a dose of 10 kJ m−2 UV-B, proportionally applied on days 3, 5, 7, and 10 days, is recommended.

Ozone and Bioactive Compounds in Grapes and Wine

Ozone is widely used in the agri-food and food processing industries mainly as a sanitizing agent. However, it has recently become clear that ozone exposition leads to another important benefit: in living tissues, the induced-oxidative stress triggers the antioxidant response, and, therefore, it enhances the production of antioxidant and stress-related secondary metabolites. As such, ozone can be considered an abiotic elicitor. The goal of the present review was to critically summarize knowledge about the possibility of improving bioactive compounds and, consequently, the health-related properties of grapes and wine, by using ozone. The greatest interest has been given not only to the pre- and post-harvest treatment of table and wine grapes, but also to the explanation of the mechanisms involved in the ozone-related response and the main secondary metabolites biosynthetic pathways. From the literature available, it is clear that the effect of ozone treatment on health-related properties and secondary metabolites accumulation depends on many factors, such as the cultivar, but also the form (water or gaseous), doses, and application method of ozone. Most of the published papers report an increase in antioxidant compounds (e.g., polyphenols) and stress-related volatiles, confirming the hypothesis that ozone could be used to improve berry and wine compositional and sensory quality.

Electrical Stimulation Enhances Plant Defense Response in Grapevine through Salicylic Acid-Dependent Defense Pathway

Concern over environmental pollution generated by chemical fungicides has led to the introduction of alternative pest management strategies to chemical fungicide application. One of those strategies is the induction of plant defense response by an abiotic elicitor. In the present study, field-grown grapevines were subjected to electrical stimulation using a solar panel from two weeks before flowering to harvest in the 2016 and 2020 growing seasons. In both years, electrical stimulation decreased the incidence of gray mold and/or ripe rot on bunches and downy mildew on leaves of the field-grown grapevine. Transcription of a gene encoding β-1,3-glucanase but not class IV chitinase in leaves of potted grapevine seedlings was upregulated 20 days after electrical stimulation, suggesting that electrical stimulation acts as an abiotic elicitor of plant defense response to fungal diseases. The gene expression of PR1 but not PDF1.2 was upregulated in Arabidopsis plants subjected to electrical stimulation. On the other hand, PR1 gene expression was not induced in salicylic acid (SA)-insensitive Arabidopsis mutant npr1-5 subjected to electrical stimulation. Taken together, electrical stimulation is responsible for plant defense response through the SA-dependent defense pathway. These findings would help us develop a novel and innovative practical technique that uses electrical stimulation in integrated pest management.

NaCl-Induced Elicitation Alters Physiology and Increases Accumulation of Phenolic Compounds in Melissa officinalis L.

In nature, plants usually produce secondary metabolites as a defense mechanism against environmental stresses. Different stresses determine the chemical diversity of plant-specialized metabolism products. In this study, we applied an abiotic elicitor, i.e., NaCl, to enhance the biosynthesis and accumulation of phenolic secondary metabolites in Melissa officinalis L. Plants were subjected to salt stress treatment by application of NaCl solutions (0, 50, or 100 mM) to the pots. Generally, the NaCl treatments were found to inhibit the growth of plants, simultaneously enhancing the accumulation of phenolic compounds (total phenolics, soluble flavonols, anthocyanins, phenolic acids), especially at 100 mM NaCl. However, the salt stress did not disturb the accumulation of photosynthetic pigments and proper functioning of the PS II photosystem. Therefore, the proposed method of elicitation represents a convenient alternative to cell suspension or hydroponic techniques as it is easier and cheaper with simple application in lemon balm pot cultivation. The improvement of lemon balm quality by NaCl elicitation can potentially increase the level of health-promoting phytochemicals and the bioactivity of low-processed herbal products.

Chitosan enhances rosmarinic acid production in shoot cultures of Melissa officinalis L. through the induction of methyl jasmonate

Background Chitosan is a polycationic polysaccharide derived from chitin that has been recognized as an effective elicitor in the production of secondary metabolites of many medicinal plants. In this study, the effect of abiotic elicitor (chitosan) at various concentrations on rosmarinic acid (RA) and total phenolic accumulation in shoot cultures of lemon balm was investigated. Results Treatment of shoots by chitosan led to a noticeable induction of phenylalanine ammonia-lyase (PAL), catalase (CAT), guaiacol peroxidase (GPX) and lipoxygenase (LOX) activities. Besides, the expression of PAL1, TAT and RAS genes and accumulation of RA and phenolic compound increased in chitosan-treated lemon balm shoots. Chitosan treatment also increased H2O2 accumulation and the expression of RBOH, an essential gene implicated in ROS production. Also, the up-regulation of the OPR gene by exogenous chitosan was associated with the induction of endogenous JA determined by GC-MASS. Conclusion The present study showed that the induced production of rosmarinic acid by chitosan involves the trigger of defense-related enzymes, up-regulated expression of TAT and RAS genes, and stimulation of JA biosynthesis.

The Study of Artemisinin Content in Callus Artemisia annua L. Cultures Elicited with Endophytic Fungi Aspergillus sp.

Artemisinin, is a sesquiterpene lactone which is originally extracted from the medicinal plant Artemisia annua L. Artemisinin is a very effective antimalarial agent, however it is produced in very low amounts in plants. Chemical synthesis of artemisinin is complicated and not economically feasible. Researchers often use elicitation methods to increase artemisinin content in a laboratory scale with biotic or abiotic elicitor. This study examined the effect of elicitation using endophytic fungi Aspergillus sp on artemisinin content of callus A. annua cultures. Observations were made on its growth, texture and color, chlorophyll content and dry weight. Fungi were isolated from the stem tissue of A. annua and callus were grown on Murashige and Skoog medium. After 3 weeks of incubation, callus treated with four different elicitors concentration (0, 2, 4, 6 mg/mL). There were significant alterations on callus culture in terms of growth, texture, color and chlorophyll content after elicitation. The results clearly demonstrated that the endophytic fungal elicitor Aspergillus sp could increase artemisinin content but did not affect the callus dry weight of A. annua. The treatment of 4 mg/mL elicitor produced the highest artemisinin content, that increased 7.6 times compared to the control, from 0.0036% to 0.0275%.

The effect of biotic and abiotic elicitors on biomass and saponin production of secondary root cultivated in shake flasks Panax vietnamensis adventitious root

Panax vietnamensis Ha et Grushv. is an endemic ginseng of Vietnam which has highly nutraceutical, medicinal and comercial values. Many its special saponins provide resistance to stress, disease and exhaustion. In this study, the biotic elicitors (yeast extract and chitosan) at concentrations from 50 – 200 mg/l and abiotic elicitors (jasmonic acid, abscisic acid and salicylic acid) at concentrations from 50 – 200 µl/l were used to evaluate the possibility of increasing secondary root’s biomass and saponin in Panax vietnamensis adventitious root cultures. This cultures were maintained on Innova 2100 shaker shaker plantform at a speed of 100 rpm, and its modified MS medium (NH4+/NO3-: 7.19/18.5 mM/mM) were supplemented with 7 mg/l IBA, 0.5 mg/l BA and 3% sucrose. Results after 56 days of cultured showed that most elicitors significantly reduced dry biomass of secondary roots as compared to control (exception the addition of 50 – 100 mg/l yeast extract or 50 µl/l salicylic acid). However, all elicitors increased saponin-accumulation, and abiotic elicitor is more effective saponin-accumulation than those biotic elicitors. Jasmonic acid obviously gave the best results; with total amount of 3 saponins at 150 µl/l, Rg1 at 100 µl/l, Rb1 at 50 µl/l and MR2 at 200 µl/l and Rg1 (3.22%), significantly higher than other concentration of elicitor. However, for accumulating saponins and developing secondary root, 150 mg/l YE is the most real effective in all elicitors (0.88 mg).