Influence of urban gardening conditions on the concentration of antioxidant secondary plant metabolites in kale

During the COVID-19 pandemic urban gardening became popular across the globe. Leafy vegetables supplement the daily diet and contribute to consumers health. Within the last decade kale (Brassica oleracea var. sabellica L.) gained popularity in urban gardening. However, shading due to unfavourable cardinal directions may reduce plant growth and accumulation of health-promoting secondary plant metabolites such as polyphenols, carotenoids andglucosinolates in kale. We compared authentic urban gardening conditions for kale grown in all four cardinal directions of a residential building. The overall concentration of carotenoids did benefit from sun exposed growing locations, including indoor cultivation behind UV light filtering glass windows, while concentrations of nutritionally important lutein did not differ among the locations and their altered growth conditions regarding abiotic stressors such as sun exposure, temperature, and water consumption. Total concentration of phenolics profited the most from direct sunlight but is severely reduced behind glass windows. Overall, satisfying growth rates of kale were achieved under all applied conditions, encouraging outdoor urban gardening with kale plants even in shaded locations

Influence of Light and Temperature on Gene Expression Leading to Accumulation of Specific Flavonol Glycosides and Hydroxycinnamic Acid Derivatives in Kale (Brassica oleracea var. sabellica)

Light intensity and temperature are very important signals for the regulation of plant growth and development. Plants subjected to less favorable light or temperature conditions often respond with accumulation of secondary metabolites. Some of these metabolites have been identified as bioactive compounds, considered to exert positive effects on human health when consumed regularly. In order to test a typical range of growth parameters for the winter crop Brassica oleracea var. sabellica, plants were grown either at 400 µmol m-2 s-1 or 100 µmol m-2 s-1 at 10°C, or at 400 µmol m-2 s-1 with 5°C or 15°C. The higher light intensity overall increased flavonol content of leaves, favoring the main quercetin glycosides, a caffeic acid monoacylated kaempferol triglycoside, and disinapoyl-gentiobiose. The higher temperature mainly increased the hydroxycinnamic acid derivative disinapoyl-gentiobiose, while at lower temperature synthesis is in favor of very complex sinapic acid acylated flavonol tetraglycosides such as kaempferol-3-O-sinapoyl-sophoroside-7-O-diglucoside. A global analysis of light and temperature dependent alterations of gene expression in B. oleracea var. sabellica leaves was performed with the most comprehensive Brassica microarray. When compared to the light experiment much less genes were differentially expressed in kale leaves grown at 5°C or 15°C. A structured evaluation of differentially expressed genes revealed the expected enrichment in the functional categories of e.g. protein degradation at different light intensities or phytohormone metabolism at different temperature. Genes of the secondary metabolism namely phenylpropanoids are significantly enriched with both treatments. Thus, the genome of B. oleracea was screened for predicted genes putatively involved in the biosynthesis of flavonoids and hydroxycinnamic acid derivatives. All identified B. oleracea genes were analyzed for their most specific 60-mer oligonucleotides present on the 2 × 105K format Brassica microrray. Expression differences were correlated to the structure-dependent response of flavonoid glycosides and hydroxycinnamic acid derivatives to alterations in either light or temperature. The altered metabolite accumulation was mainly reflected on gene expression level of core biosynthetic pathway genes and gave further hints to an isoform specific functional specialization

Comparative evaluation of total antioxidant capacities of plant polyphenols.

Thirty‐seven samples of naturally occurring phenolic compounds were evaluated using three common in vitro assays for total antioxidant activity (TAC) testing: the Trolox Equivalent Antioxidant Capacity (TEAC), the Ferric Reducing Antioxidant Potential (FRAP) and the 2,2‐ diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging assay, in addition to the Folin‐Ciocalteu reagent reactivity (FCR). We found that antioxidant hierarchies depended on the choice of assay and applied ANOVA analyses to explore underlying structure‐TAC dependencies. In addition tostatistically confirming the empirically established connection between flavonoid ring‐B catechol and high TEAC or FRAP, new correlations were also found. In flavonoids, (i) hydroxyl groups on ring‐B had a positive effect on all four TAC assays; (ii) the presence of a 3‐hydroxyl group on ring‐C increased TEAC and FRAP, but had no effect on DPPH or FCR; (iii) Phenolic acids lacking a 3‐hydroxyl group had significantly lower FRAP or DPPH than compounds having this structure, while TEAC or FCR were not affected. Results demonstrated that any TAC‐based ranking of phenolic rich samples would very much depend on the choice of assay, and argue for use of more than one technique. As an illustration, we compared results of the above four assays using either grapevine leaf extracts or synthetic mixtures of compounds prepared according to major polyphenols identified in the leaves

UV-B Pre-treatment Alters Phenolics Response to Monilinia fructicola Infection in a Structure-Dependent Way in Peach Skin

Phenolic compounds represent a large class of secondary metabolites, involved in multiple functions not only in plant life cycle, but also in fruit during post-harvest. phenolics play a key role in the response to biotic and abiotic stresses, thus their accumulation is regulated by the presence of environmental stimuli. The present work aimed to investigate how different pre-UV-B-exposures can modulate the phenolic response of peach fruit infected with Monilinia fructicola. Through HPLC-DAD-MSn, several procyanidins, phenolic acids, flavonols, and anthocyanins were detected. Both UV-B radiation and fungal infection were able to stimulate the accumulation of phenolics, dependent on the chemical structure. Regarding UV-B exposure, inoculated with sterile water, 3 h of UV-B radiation highest concentration of phenolics was found, especially flavonols and cyanidin-3-glucoside far from the wound. However, wounding decreased the phenolics in the region nearby. When peaches were pre-treated with 1 h of UV-B radiation, the fungus had an additive effect in phenolic accumulation far from the infection, while it had a subtractive effect with 3 h of UV-B radiation, especially for flavonols. Canonical discriminant analysis and Pearson correlation revealed that all phenolic compounds, except procyanidin dimer, were highly regulated by UV-B radiation, with particularly strong correlation for quercetin and kaempferol glycosides, while phenolics correlated with the fungus infection were quercetin-3-galactoside, quercetin-3-glucoside, kaempferol-3-galactoside and isorhamnetin-3-glucoside. Modulation of pathogen-induced phenolics also far from inoculation site might suggest a migration of signaling molecules from the infected area to healthy tissues

Toxicity, Antioxidant Activity, and Phytochemicals of Basil (Ocimum basilicum L.) Leaves Cultivated in Southern Punjab, Pakistan

Basil (Ocimum basilicum L.) is one of the most common aromatic herbs, a rich source of bioactive compounds, and is used extensively to add aroma and flavor to food. The leaves, both in fresh and dried form, are used as a culinary ingredient in different cultures. O. basilicum is also famous for its therapeutic potential and preservation effects. The present study investigated the cytotoxicity of basil at three different growth stages (GS), i.e., GS-1 (58 days of growth), GS-2 (69 days of growth), and GS-3 (93 days of growth) using the brine shrimp lethality assay. The results revealed that cytotoxicity was influenced by GS and the concentration of extracts. Aqueous extracts of basil at a concentration of 10 to 1000 µg/mL did not show notable toxicity. The lowest mortality rate, i.e., 8.9%, was recorded for GS-2 at the highest tested dose of basil extracts. The mortality rate at GS-1, GS-2, and GS-3 was found to be 26.7 ± 3.34%, 8.91 ± 0.10%, and 16.7 ± 0.34%, respectively, at 1000 µg/mL. GS-2 basil powder with the lowest toxicological risk was extracted with different solvents, viz., n-hexane, dichloromethane, ethanol, and water. The highest concentration of plant secondary metabolites including total phenolic acid, flavonoids, and tannin content was observed in ethanol extracts. Ethanol extracts also exhibited the highest antioxidant activity in DPPH, FRAP and H2O2 assays. LC-ESI-MS/MS analysis presented ethanol extracts of basil as a promising source of known health-promoting and therapeutic compounds such as rosmarinic acid, ellagic acid, catechin, liquiritigenin, and umbelliferone. The results suggest basil, a culinary ingredient, as a potential source of bioactive compounds which may offer an array of health promoting and therapeutic properties

Corrigendum: UV-B Pre-treatment Alters Phenolics Response to Monilinia fructicola Infection in a Structure-Dependent Way in Peach Skin

[This corrects the article DOI: 10.3389/fpls.2018.01598.]

The transgenerational effects of solar short-UV radiation differed in two accessions of Vicia faba L. from contrasting UV environments

Background and aims: UVB radiation can rapidly induce gene regulation leading to cumulative changes for plant physiology and morphology. We hypothesized that a transgenerational effect of chronic exposure to solar short UV modulates the offspring's responses to UVB and blue light, and that the transgenerational effect is genotype dependent. Methods: We established a factorial experiment combining two Vicia faba L. accessions, two parental UV treatments (full sunlight and exclusion of short UV, 290-350 nm), and four offspring light treatments from the factorial combination of UVB and blue light. The accessions were Aurora from southern Sweden, and ILB938 from Andean region of Colombia and Ecuador. Key results: The transgenerational effect influenced morphological responses to blue light differently in the two accessions. In Aurora, when UVB was absent, blue light increased shoot dry mass only in plants whose parents were protected from short UV. In ILB938, blue light increased leaf area and shoot dry mass more in plants whose parents were exposed to short UV than those that were not. Moreover, when the offspring was exposed to UVB, the transgenerational effect decreased in ILB938 and disappeared in Aurora. For flavonoids, the transgenerational effect was detected only in Aurora: parental exposure to short UV was associated with a greater induction of total quercetin in response to UVB. Transcript abundance was higher in Aurora than in ILB938 for both CHALCONE SYNTHASE (99-fold) and DON-GLUCOSYLTRANSFERASE 1 (19-fold). Conclusions: The results supported both hypotheses. Solar short UV had transgenerational effects on progeny responses to blue and UVB radiation, and they differed between the accessions. These transgenerational effects could be adaptive by acclimation of slow and cumulative morphological change, and by early build-up of UV protection through flavonoid accumulation on UVB exposure. The differences between the two accessions aligned with their adaptation to contrasting UV environments.Peer reviewe

Influence of UV radiation-absorbing foils on secondary plant metabolites in three lettuce cultivars (Lactuca sativa L. and Cichorium intybus L.)

Introduction: Providing fresh and healthy vegetables, produced locally and under climate-friendly conditions, is a major challenge for future agriculture. The usage of foil tunnels prolongs cultivation periods in colder climates and reduces abiotic and biotic stress factors during crop growth, but it may also affect nutritional value and consumer perception due to the altered light spectrum.Methods and results: Three different foils, one with low UV transmission, another with reduced UVB transmission, and a control foil with high UV transmission, were used to modulate light conditions for three different lettuce cultivars [radicchio type (cv. Indigo), romaine type (cv. Attico), and butterhead type (cv. Larissa)]. Taste-relevant sesquiterpene lactones and health-relevant carotenoids and polyphenols were measured by high-performance liquid chromatography, which revealed that light conditions are widely irrelevant for carotenoid concentrations. However, when UV-shielding foils were used, there was an up to 66% decrease in total polyphenol concentration. Less reduction could be achieved through the use of partially UV-transmissive foils. Sesquiterpene lactone concentrations were higher in plants under UV-blocking foils, when radicchio-type lettuce, naturally rich in sesquiterpene lactones, was cultivated.Discussion: It is noteworthy that the sesquiterpene lactone lactucopicrin had a negative correlation with UVB intensities, while lactucin was unaffected. The nutritional value, measured by three different antioxidant activity assays, also benefited from an optimized foil choice with higher UV transmission