Isoflavone accumulation and the metabolic gene expression in response to persistent UV-B irradiation in soybean sprouts

The Effect of Illumination Patterns during Mung Bean Seed Germination on the Metabolite Composition of the Sprouts

Mung bean (Vigna radiata (L.) Wilczek) sprouts are popular over the world because of their taste, nutritional value, well-balanced biochemical composition, and other properties beneficial for human health. Germination conditions affect the composition of metabolites in mung bean sprouts, so a detailed study into its variability is required. This article presents the results of a comparison of the metabolite composition in the leaves of mung bean sprouts germinated first in the dark (DS) and then in the light (LS). Gas chromatography with mass spectrometry (GC-MS) made it possible to identify more than 100 compounds representing various groups of phytochemicals. Alcohols, amino acids, and saccharides predominated in the total amount of compounds. The analysis of metabolomic profiles exposed a fairly high intra- and intervarietal variability in the metabolite content. DS and LS differed in the qualitative and quantitative content of the identified compounds. The intravarietal variability was more pronounced in DS than in LS. DS demonstrated higher levels of saccharides, fatty acids, acylglycerols, and phenolic compounds, while amino acids were higher in LS. Changes were recorded in the quantitative content of metabolites participating in the response of plants to stressors-ornithine, proline, GABA, inositol derivatives, etc. The changes were probably induced by the stress experienced by the sprouts when they were transferred from shade to light. The analysis of variance and principal factor analysis showed the statistically significant effect of germination conditions on the content of individual compounds in leaves. The identified features of metabolite variability in mung bean genotypes grown under different conditions will contribute to more accurate selection of an illumination pattern to obtain sprouts with desirable biochemical compositions for use in various diets and products with high nutritional value.

Recent developments in applications of physical fields for microbial decontamination and enhancing nutritional properties of germinated edible seeds and sprouts: a review

Germinated edible seeds and sprouts have attracted consumers because of their nutritional values and health benefits. To ensure the microbial safety of the seed and sprout, emerging processing methods involving physical fields (PFs), having the characteristics of high efficiency and environmental safety, are increasingly proposed as effective decontamination processing technologies. This review summarizes recent progress on the application of PFs to germinating edible seeds, including their impact on microbial decontamination and nutritional quality and the associated influencing mechanisms in germination. The effectiveness, application scope, and limitation of the various physical techniques, including ultrasound, microwave, radio frequency, infrared heating, irradiation, pulsed light, plasma, and high-pressure processing, are symmetrically reviewed. Good application potential for improving seed germination and sprout growth is also described for promoting the accumulation of bioactive compounds in sprouts, and subsequently enhancing the antioxidant capacity under favorable PFs processing conditions. Moreover, the challenges and future directions of PFs in the application to germinated edible seeds are finally proposed. This review also attempts to provide an in-depth understanding of the effects of PFs on microbial safety and changes in nutritional properties of germinating edible seeds and a theoretical reference for the future development of PFs in processing safe sprouted seeds.

A Review of Classification, Biosynthesis, Biological Activities and Potential Applications of Flavonoids

Flavonoids represent the main class of plant secondary metabolites and occur in the tissues and organs of various plant species. In plants, flavonoids are involved in many biological processes and in response to various environmental stresses. The consumption of flavonoids has been known to reduce the risk of many chronic diseases due to their antioxidant and free radical scavenging properties. In the present review, we summarize the classification, distribution, biosynthesis pathways, and regulatory mechanisms of flavonoids. Moreover, we investigated their biological activities and discuss their applications in food processing and cosmetics, as well as their pharmaceutical and medical uses. Current trends in flavonoid research are also briefly described, including the mining of new functional genes and metabolites through omics research and the engineering of flavonoids using nanotechnology. This review provides a reference for basic and applied research on flavonoid compounds.

The Classification, Molecular Structure and Biological Biosynthesis of Flavonoids, and Their Roles in Biotic and Abiotic Stresses

With the climate constantly changing, plants suffer more frequently from various abiotic and biotic stresses. However, they have evolved biosynthetic machinery to survive in stressful environmental conditions. Flavonoids are involved in a variety of biological activities in plants, which can protect plants from different biotic (plant-parasitic nematodes, fungi and bacteria) and abiotic stresses (salt stress, drought stress, UV, higher and lower temperatures). Flavonoids contain several subgroups, including anthocyanidins, flavonols, flavones, flavanols, flavanones, chalcones, dihydrochalcones and dihydroflavonols, which are widely distributed in various plants. As the pathway of flavonoid biosynthesis has been well studied, many researchers have applied transgenic technologies in order to explore the molecular mechanism of genes associated with flavonoid biosynthesis; as such, many transgenic plants have shown a higher stress tolerance through the regulation of flavonoid content. In the present review, the classification, molecular structure and biological biosynthesis of flavonoids were summarized, and the roles of flavonoids under various forms of biotic and abiotic stress in plants were also included. In addition, the effect of applying genes associated with flavonoid biosynthesis on the enhancement of plant tolerance under various biotic and abiotic stresses was also discussed.

UV-B radiation enhances isoflavone accumulation and antioxidant capacity of soybean calluses

Isoflavones are a class of flavonoids that belong to a large family of polyphenols and synthesized predominantly in legume, and they play important roles including acting as antioxidant, preventing osteoporosis, reducing the risk of atherosclerosis, and protecting against cardiovascular disease. This study focused on the accumulation and synthetic metabolism of isoflavone in soybean hypocotyl and cotyledon calluses under UV-B radiation. The results showed that UV-B radiation significantly up-regulated the gene expression of phenylalanine ammonia lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), chalcone ketone synthase (CHS), chalcone isomerase (CHI), and isoflavone synthase (IFS), and enhanced their activity in soybean hypocotyl and cotyledon calluses. As a result, isoflavones content increased by 21.23 and 21.75% in soybean hypocotyl and cotyledon calluses, respectively. Among the isoflavones produced, malonyldaidzin was the dominant one in hypocotyl callus, while malonylglycitin and daidzein were the main isoflavones in cotyledon calluses. This study revealed that UV-B radiation induced isoflavone accumulation in soybean calluses, which could be an efficient strategy to improve the nutritional value of food and produce high levels of bioactive secondary metabolites.

Tissue-Specific Antioxidant Activities of Germinated Seeds in Lentil Cultivars during Thermal Processing

Nongerminated seeds (NGS) and germinated seeds (GS) of lentils are regularly eaten after thermal processing. However, the effect of these high temperatures on the beneficial antioxidants present in seeds is unknown. This study examined the effects of thermal processing on the color, polyphenol content, and antioxidant activity (AA) of the seeds of three different cultivars of lentils, including two with seed coats, French green (FG) and Lentil green (LG), and one without a seed coat, Lentil red (LR). Regardless of the cultivars and processing temperatures, the GS tended to be clearer and less yellow than the NGS. The GS of the FG and LG showed lower levels of total phenolic content, major flavonoid content (kaempferol, luteolin, and myricetin), and AA than the NGS. On the other hand, the LR displayed the opposite trend, with the above indicators being higher in the GS than in the NGS. As the values in the germinated endosperm tended to increase, it was concluded that the decrease in AA in the FG and LG was caused by the reduction in antioxidants in the seed coat. Although the temperature had nonsignificant effects on the majority of the antioxidants in the NGS and GS of different lentil cultivars, an 80 °C treatment yielded the highest value of AA in the GS of FG and LG. The results of a correlation coefficient analysis demonstrated the significance of the content of kaempferol, total flavonoids, and total phenolics examined for this experiment as contributors to AA in lentil tissues.

Red and blue light-specific metabolic changes in soybean seedlings

Red and blue artificial light sources are commonly used as photosynthetic lighting in smart farm facilities, and they can affect the metabolisms of various primary and secondary metabolites. Although the soybean plant contains major flavonoids such as isoflavone and flavonol, using light factors to produce specific flavonoids from this plant remains difficult because the regulation of light-responded flavonoids is poorly understood. In this study, metabolic profiling of soybean seedlings in response to red and blue lights was evaluated, and the isoflavone-flavonol regulatory mechanism under different light irradiation periods was elucidated. Profiling of metabolites, including flavonoids, phenolic acids, amino acids, organic acids, free sugars, alcohol sugars, and sugar acids, revealed that specific flavonol, isoflavone, and phenolic acid showed irradiation time-dependent accumulation. Therefore, the metabolic gene expression level and accumulation of isoflavone and flavonol were further investigated. The light irradiation period regulated kaempferol glycoside, the predominant flavonol in soybeans, with longer light irradiation resulting in higher kaempferol glycoside content, regardless of photosynthetic lights. Notably, blue light stimulated kaempferol-3-O-(2,6-dirhamnosyl)-galactoside accumulation more than red light. Meanwhile, isoflavones were controlled differently based on isoflavone types. Malonyl daidzin and malonyl genistin, the predominant isoflavones in soybeans, were significantly increased by short-term red light irradiation (12 and 36 h) with higher expressions of flavonoid biosynthetic genes, which contributed to the increased total isoflavone level. Although most isoflavones increased in response to red and blue lights, daidzein increased in response only to red light. In addition, prolonged red light irradiation downregulated the accumulation of glycitin types, suggesting that isoflavone's structural specificity results in different accumulation in response to light. Overall, these findings suggest that the application of specific wavelength and irradiation periods of light factors enables the regulation and acquisition of specialized metabolites from soybean seedlings.

Chickpea and Lupin Sprouts, Stimulated by Different LED Lights, As Novel Examples of Isoflavones-Rich Functional Food, and Their Impact on Breast and Prostate Cells

Among all legumes sprouts' active compounds, isoflavones seem to be the most important; nevertheless, their high content is not always associated with beneficial effects. These compounds may prevent or stimulate hormone-dependent cancers due to their estrogen-like activity. Different LED light quality can change the synthesis of active compounds and significantly influence the biological activity of the sprouts. This study aimed to evaluate the effects of LED light (red, blue, green, yellow), as well as total darkness, and natural light conditions (as reference), on isoflavones content, determined by HPLC-UV-VIS, during 10 days of harvesting of chickpea and lupin sprouts. Due to the ambiguous estrogenic potential of isoflavones, the impact of these sprouts on normal and cancer prostate and breast cells was evaluated. Yellow LED light resulted in the highest sum of isoflavones in chickpea sprouts (up to 1 g/100 g dw), while for green LED light, the isoflavones sum was the lowest. The exact opposite effect was noted for lupin sprouts, with the predominance of green over the yellow LED light. The examined sprouts were of high safety to non-neoplastic breast and prostate cells, with interesting cytotoxic effects on breast MCF7 and prostate DU145 cancer cells. No clear relationship was observed between the activity and isoflavones content.

Nitric oxide mediates melatonin-induced isoflavone accumulation and growth improvement in germinating soybeans under NaCl stress

The involvement of nitric oxide (NO) in exogenous melatonin (MT)-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans was investigated in this study. The results demonstrated that MT increased the activity of nitrate reductase (NR) and upregulated the relative expression of NR1, NR2, and nitric oxide synthase1, which subsequently led to an increase in NO content. MT and sodium nitroprusside (SNP, as an NO donor) markedly increased isoflavone content by enhancing the activities of cinnamic acid 4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL), and by upregulating gene expression of C4H, Isoflavone synthase, PAL, and Chalcone isomerase 1A, which are involved in isoflavone biosynthesis. Moreover, MT, as well as SNP, improved the growth and biomass of NaCl-treated soybeans by increasing the activities of superoxide dismutase, catalase, and peroxidase, and reducing the accumulation of H₂O₂ and O₂^•- in soybeans under NaCl stress. These MT-induced responses were entirely reversed by the supply of 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a specific scavenger of NO), which in turn considerably decreased endogenous NO content. These results suggest that NO acts as an important downstream signal molecule, mediating MT-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans.

Changes in Quercetin Derivatives and Antioxidant Activity in Marigold Petals (Tagetes patula L.) Induced by Ultraviolet-B Irradiation and Methyl Jasmonate

Marigold petals contain numerous antioxidative flavonoids and carotenoids that can be affected by environmental stressors. There is yet no detailed study on the relationship between phytochemical accumulation and stressors in marigold petals. This study evaluated quercetin derivatives and antioxidant activity in marigold petals in response to ultraviolet-B (UV-B) irradiation and methyl jasmonate (MeJA) treatment. The limiting UV-B radiation intensity and MeJA dose that caused no wilting damage under 1-h daily treatment for 10 days were <2 W∙m−2∙s−1 and <10 mM, respectively. Marigold petals contained three major flavonoids, quercetin-7-O-glucoside (Q7G, 6.6 mg∙g−1dw), quercetin-3-O-glucoside (Q3G, 62.7 mg), and quercetin (26.6 mg), possessing different antioxidant potential and exhibiting the highest power in quercetin and next value in Q7G. Single UV-B irradiation exerted a limited effect on the changes in the content of the three quercetin derivatives, whereas combined treatment with 1 W UV-B radiation and 5 mM MeJA resulted in the highest total quercetin content, showing >20% increase compared to that without treatment. This increase primarily resulted in an increase in quercetin content. MeJA treatment positively affected the increase in Q3G and Q7G contents in a dose-dependent manner during the 10-d experimental period but exerted no considerable effect on quercetin accumulation. The antioxidant activity was increased when flowers were exposed to mild MeJA treatment of 5−10 mM. UV-B irradiation decreased the antioxidant activity of marigold petals, but this decrease could be compensated by MeJA treatment.

Health-Promoting Phenolic Compound Accumulation, Antioxidant Response, Endogenous Salicylic Acid Generation, and Biosynthesis Gene Expression in Germinated Pigeon Pea Seeds Treated with UV-B Radiation

Germinated pigeon pea seeds (GPPSs) are good dietary supplements with satisfactory nutritional and medicinal values. In this study, UV-B treatment was used to promote the accumulation of health-promoting phenolic compounds (10 flavonoids and 1 stilbene) in GPPS. The total yield of 11 phenolic compounds (235 839.76 ± 17 118.24 ng/g DW) significantly improved (2.53-fold increase) in GPPSs exposed to UV-B radiation (3 W/m2) for 8 h, whereas free amino acid and reducing sugar contents exhibited a decreasing tendency during UV-B exposure. Meanwhile, the positive response in the antioxidant activities of enzymes and nonenzymatic extracts was noticed in UV-B-treated GPPSs. Moreover, UV-B radiation could cause tissue damages in hypocotyls and cotyledons of the GPPSs and enhance the generation of endogenous salicylic acid, thus activating the expression of biosynthesis genes (especially CHS and STS1). Overall, the simple UV-B supplementation strategy makes GPPSs more attractive as functional foods/nutraceuticals in diet for promoting human health.

Occurrence of isoflavones in soybean sprouts and strategies to enhance their content: A review

Sprouting is a common strategy to enhance the nutritional value of seeds. Here, all the reports regarding the occurrence of isoflavones in soybean sprouts have been covered for the first time. Isoflavones were detected with concentrations ranging from 1 × 10-2 to 1 × 101  g/kg in soybean sprouts. Isoflavone concentration depends on the cultivar, germination time, part of the sprout, light, and temperature. Aglycon isoflavones increased during germination, especially in the hypocotyl, while 6″-O-malonyl-7-O-β-glucoside isoflavones decreased in the hypocotyl and increased in the cotyledon and root. Cooking reduced total isoflavone content. Regarding the strategies to enhance isoflavone contents, fermentation with Aspergillus sojae and external irradiation with UV-A or far-infrared were the methods that caused the greatest increases in aglycon, 7-O-β-glucoside, and total isoflavones. However, the largest increases in 6″-O-malonyl-7-O-β-glucoside and 6″-O-acetyl-7-O-β-glucosides isoflavones were detected after treatment with chitohexaose and calcium chloride, respectively. PRACTICAL APPLICATION: Soybean sprouts are widely consumed and provide essential proteins, antioxidants, and minerals. They are rich in isoflavones, which exhibit numerous health benefits, and have been studied as alternative therapies for a range of hormone-dependent conditions, such as cancer, menopausal symptoms, cardiovascular disease, and osteoporosis. Despite numerous reports being published to date regarding the occurrence of isoflavones in soybean sprouts, the publications in this field are highly dispersed, and a review has not yet been published. This review aims to (1) highlight the particular isoflavones that have been detected in soybean sprouts and their concentrations, (2) compared the effects of temperature, light, cooking and soybean cultivar affect the isoflavone levels on the different parts of the sprout, and (3) discuss the efficacy of the methods to enhance isoflavone contents. This review will provide a better understanding of the current state of this field of research by comparing the general trends and the different treatments for soybean sprouts.

UV and Visible Spectrum LED Lighting as Abiotic Elicitors of Bioactive Compounds in Sprouts, Microgreens and Baby Leaves. A Comprehensive Review Including Their Mode of Action

According to social demands, the agri-food industry must elaborate convenient safe and healthy foods rich in phytochemicals while minimising processing inputs like energy consumption. Young plants in their first stages of development represent great potential. Objective: This review summarises the latest scientific findings concerning the use of UV and visible spectrum LED lighting as green, sustainable, and low-cost technologies to improve the quality of sprouts, microgreens, and baby leaves to enhance their health-promoting compounds, focusing on their mode of action while reducing costs and energy. Results: These technologies applied during growing and/or after harvesting were able to improve physiological and morphological development of sprouted seeds while increasing their bioactive compound content without compromising safety and other quality attributes. The novelty is to summarise the main findings published in a comprehensive review, including the mode of action, and remarking on the possibility of its postharvest application where the literature is still scarce. Conclusions: Illumination with UV and/or different regions of the visible spectrum during growing and shelf life are good abiotic elicitors of the production of phytochemicals in young plants, mainly through the activation of specific photoreceptors and ROS production. However, we still need to understand the mechanistic responses and their dependence on the illumination conditions.

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.

Edible Plant Sprouts: Health Benefits, Trends, and Opportunities for Novel Exploration

The consumption of plant sprouts as part of human day-to-day diets is gradually increasing, and their health benefit is attracting interest across multiple disciplines. The purpose of this review was to (a) critically evaluate the phytochemicals in selected sprouts (alfalfa, buckwheat, broccoli, and red cabbage), (b) describe the health benefits of sprouts, (c) assess the recent advances in sprout production, (d) rigorously evaluate their safety, and (e) suggest directions that merit special consideration for further novel research on sprouts. Young shoots are characterized by high levels of health-benefitting phytochemicals. Their utility as functional ingredients have been extensively described. Tremendous advances in the production and safety of sprouts have been made over the recent past and numerous reports have appeared in mainstream scientific journals describing their nutritional and medicinal properties. However, subjects such as application of sprouted seed flours in processed products, utilizing sprouts as leads in the synthesis of nanoparticles, and assessing the dynamics of a relationship between sprouts and gut health require special attention for future clinical exploration. Sprouting is an effective strategy allowing manipulation of phytochemicals in seeds to improve their health benefits.

Periodical UV-B radiation hormesis in biosynthesis of kale sprouts nutraceuticals

The objective of the present study was to evaluate the periodical UV-B radiation hormesis during kale seeds germination in their main content of secondary metabolite compounds (phenols; glucosinolates; total antioxidant capacity -TAC-) and their changes during a refrigerated shelf-life. The total UV-B doses received were 0, 5, 10, and 15 kJ m^-2 (CTRL, UVB5, UVB10, and UVB15) in where the 25% was applied on the 3rd, 5th, 7th, and 10th sprouting day. UV radiation did not affect the morphological development of the sprouts. UVB10 and UVB15 treatments increased their phenolic content (>30%). Likewise, TAC was increased by UV-B lighting ~10% (DPPH) and ~20% (FRAP). The hydroxycinnamic acid content in UVB15-treated sprouts increased by 52%, while UVB5 reported an increase of 34% in the kaempferol-3,7-di-O-glucoside concentration, compared to CTRL. After 10 d at 4 °C of shelf-life, content of gallic acid hexoside I and gallic acid increased by 55 and 78% compared to UV-untreated kale sprouts, respectively. Glucoraphanin was the main glucosinolate found in kale sprouts and seeds, followed by 4-hydroxy-glucobrassicin, whose biosynthesis was enhanced by UVB10 (~24 and ~27%) and UVB15 (~36 and ~30%), respectively, compared to CTRL. In conclusion, periodical low UV-B illumination represents a useful tool to stimulate phytochemicals biosynthesis in kale sprouts as an important source of bioactive compounds with potential health benefits.

Effects of UV-A radiation on organ-specific accumulation and gene expression of isoflavones and flavonols in soybean sprout

Organ-specific flavonoid destination in soybean sprouts following UV irradiation is still unclear although the metabolic pathway of flavonoid synthesis and UV responded flavonoid accumulation have been well investigated. We report the identification of organ-specific localization and specific gene expression of isoflavones and kaempferol glycosides in the soybean sprouts responded to UV-A irradiation. UV-A irradiation stimulated only root isoflavones, especially increase of genistein types. The daidzein types predominated in non-UV-A treated roots. Kaempferol glycosides were not increased in roots by UV-A, but distinctly increased in aerial organs, especially in the cotyledons. These results demonstrate that UV-A upregulates the naringenin pathway synthesizing genistin and kaempferol rather than the liquiritigenin pathway synthesizing daidzin and glycitin. High GmUGT9 and other gene expression related to isoflavone synthesis in roots clearly demonstrate the UV-A-induced isoflavone accumulation. Aerial organ specific increase of GmF3H, GmFLS1, and GmDFR1 expression by UV-A distinctly demonstrates the flavonol increase in aerial organs.

Antioxidant Contributors in Seed, Seed Coat, and Cotyledon of γ-ray-Induced Soybean Mutant Lines with Different Seed Coat Colors

The development of soybean with high antioxidant activities for use in the food and cosmetics industries is a target of breeding programs. In soybean, antioxidants are associated with seed color, although the metabolic basis for seed coloration remains incompletely understood. We selected six γ-ray-induced mutant lines that exhibited black, partially black, brown, partially brown, or yellowish-white pigmentation in the seed coat. Antioxidant activity and contents of anthocyanins, flavan-3-ols, and isoflavones were evaluated in the seed coat and cotyledons. The lines with black or brown seeds showed the highest antioxidant activities. The cotyledons showed no significant differences in seed coat components or antioxidant activities among lines. Black and brown seed coat components showed the highest antioxidant activities. The black seed coat contained five anthocyanins, whereas seed coats of brown- and yellow-seeded lines entirely lacked anthocyanins. Both black and brown seeds were rich in flavan-3-ols, including catechin and epicatechin, which were the predominant antioxidant contributors in brown seeds. Isoflavone contents showed weaker correlations with antioxidant activity than anthocyanins and flavan-3-ols. These results demonstrated that antioxidant activities were determined by anthocyanins in black seeds and flavan-3-ols in brown and black seeds, whereas relatively low antioxidant activities in yellow seeds reflected their high isoflavone contents.

Exogenous Serotonin and Melatonin Regulate Dietary Isoflavones Profoundly through Ethylene Biosynthesis in Soybean [Glycine max (L.) Merr.]

Serotonin and melatonin are important signaling and stress mitigating molecules. However, their role and molecular mechanism in the accumulation of isoflavones are not clearly defined. To elucidate their functions, serotonin and melatonin were applied to in vitro cultures of soybean at different concentrations and analyzed to assess the accumulation of isoflavone content followed by transcript levels of biosynthesis genes at different time intervals. Increased total phenolics, total flavonoids, and different forms of isoflavone content were observed in the treatments. Expression levels of critical genes in isoflavone, ethylene, jasmonic acid, abscisic acid, and melatonin biosynthesis and related transcription factor were quantified. A correlation was observed between the expression of ethylene biosynthesis genes (S-adenosylmethionine synthase and 1-aminocyclopropane-1-carboxylate oxidase) and isoflavone biosynthesis genes (chalcone synthase, chalcone reductase, and isoflavone synthase). We hypothesize that, under serotonin and melatonin treatments, ethylene biosynthesis may play a role in the increase/decrease in isoflavone content in soybean culture.

Light signaling and UV-B-mediated plant growth regulation

Light plays an important role in plants' growth and development throughout their life cycle. Plants alter their morphological features in response to light cues of varying intensity and quality. Dedicated photoreceptors help plants to perceive light signals of different wavelengths. Activated photoreceptors stimulate the downstream signaling cascades that lead to extensive gene expression changes responsible for physiological and developmental responses. Proteins such as ELONGATED HYPOCOTYL5 (HY5) and CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) act as important factors which modulate light-regulated gene expression, especially during seedling development. These factors function as central regulatory intermediates not only in red, far-red, and blue light pathways but also in the UV-B signaling pathway. UV-B radiation makes up only a minor fraction of sunlight, yet it imparts many positive and negative effects on plant growth. Studies on UV-B perception, signaling, and response in plants has considerably surged in recent times. Plants have developed different strategies to use UV-B as a developmental cue as well as to withstand high doses of UV-B radiation. Plants' responses to UV-B are an integration of its cross-talks with both environmental factors and phytohormones. This review outlines the current developments in light signaling with a major focus on UV-B-mediated plant growth regulation.

Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration

Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health.