Ultraviolet-B radiation applied to detached peach fruit: A study of free radical generation by EPR spin trapping

Anything New under the Sun? An Update on Modulation of Bioactive Compounds by Different Wavelengths in Agricultural Plants

Plants continuously rely on light as an energy source and as the driver of many processes in their lifetimes. The ability to perceive different light radiations involves several photoreceptors, which in turn activate complex signalling cascades that ultimately lead to a rearrangement in plant metabolism as an adaptation strategy towards specific light conditions. This review, after a brief summary of the structure and mode of action of the different photoreceptors, introduces the main classes of secondary metabolites and specifically focuses on the influence played by the different wavelengths on the content of these compounds in agricultural plants, because of their recognised roles as nutraceuticals.

Growth and Bioactive Compound Content of Glehnia littoralis Fr. Schmidt ex Miquel Grown under Different CO2 Concentrations and Light Intensities

This study aims to determine the effect of different CO2 concentrations and light intensities on the growth, photosynthetic rate, and bioactive compound content of Glehnia littoralis Fr. Schmidt ex Miquel in a closed-type plant production system (CPPS). The plants were transplanted into a deep floating technique system with recycling nutrient solution (EC 1.0 dS·m-1 and pH 6.5) and cultured for 96 days under a temperature of 20 ± 1 °C, a photoperiod of 12/12 h (light/dark), and RGB LEDs (red:green:blue = 7:1:2) in a CPPS. The experimental treatments were set to 500 or 1500 µmol∙mol-1 CO2 concentrations in combination with one of the three light intensities: 100, 200, or 300 µmol∙m-2∙s-1 photosynthetic photon flux density (PPFD). The petiole length of G. littoralis was the longest in the 500 µmol∙mol-1 CO2 concentration with the 100 µmol∙m-2∙s-1 PPFD. The fresh weight (FW) and dry weight (DW) of shoots and roots were the heaviest in the 300 µmol∙m-2∙s-1 PPFD regardless of the CO2 concentration. Higher CO2 concentrations and light intensities produced the greatest photosynthetic rates. However, the SPAD value was not significantly different between the treatments. Higher light intensities produced greater content per biomass of chlorogenic acid and total saponin, although the concentration per DW or FW was not significantly different between treatments. The first and second harvest yields were the greatest in the 300 µmol∙m-2∙s-1 PPFD, regardless of the CO2 concentration. These results show that the 300 µmol∙m-2∙s-1 PPFD enhanced the growth, photosynthetic rate, and bioactive compound accumulation of G. littoralis, regardless of the CO2 concentration in a CPPS.

Stone Fruit as Biofactories of Phytochemicals With Potential Roles in Human Nutrition and Health

Phytochemicals or secondary metabolites present in fruit are key components contributing to sensory attributes like aroma, taste, and color. In addition, these compounds improve human nutrition and health. Stone fruits are an important source of an array of secondary metabolites that may reduce the risk of different diseases. The first part of this review is dedicated to the description of the main secondary organic compounds found in plants which include (a) phenolic compounds, (b) terpenoids/isoprenoids, and (c) nitrogen or sulfur containing compounds, and their principal biosynthetic pathways and their regulation in stone fruit. Then, the type and levels of bioactive compounds in different stone fruits of the Rosaceae family such as peach (Prunus persica), plum (P. domestica, P. salicina and P. cerasifera), sweet cherries (P. avium), almond kernels (P. dulcis, syn. P. amygdalus), and apricot (P. armeniaca) are presented. The last part of this review encompasses pre- and postharvest treatments affecting the phytochemical composition in stone fruit. Appropriate management of these factors during pre- and postharvest handling, along with further characterization of phytochemicals and the regulation of their synthesis in different cultivars, could help to increase the levels of these compounds, leading to the future improvement of stone fruit not only to enhance organoleptic characteristics but also to benefit human health.

Revealing mechanisms of salinity tissue tolerance in succulent halophytes: A case study for Carpobrotus rossi

Efforts to breed salt tolerant crops could benefit from investigating previously unexplored traits. One of them is a tissue succulency. In this work, we have undertaken an electrophysiological and biochemical comparison of properties of mesophyll and storage parenchyma leaf tissues of a succulent halophyte species Carpobrotus rosii ("pigface"). We show that storage parenchyma cells of C. rossii act as Na⁺ sink and possessed both higher Na⁺ sequestration (298 vs. 215 mM NaCl in mesophyll) and better K⁺ retention ability. The latter traits was determined by the higher rate of H⁺ -ATPase operation and higher nonenzymatic antioxidant activity in this tissue. Na⁺ uptake in both tissues was insensitive to either Gd³⁺ or elevated Ca²⁺ ruling out involvement of nonselective cation channels as a major path for Na⁺ entry. Patch-clamp experiments have revealed that Caprobrotus plants were capable to downregulate activity of fast vacuolar channels when exposed to saline environment; this ability was higher in the storage parenchyma cells compared with mesophyll. Also, storage parenchyma cells have constitutively lower number of open slow vacuolar channels, whereas in mesophyll, this suppression was inducible by salt. Taken together, these results provide a mechanistic basis for efficient Na⁺ sequestration in the succulent leaf tissues.

Transcriptome profiling of genes related to light-induced anthocyanin biosynthesis in eggplant (Solanum melongena L.) before purple color becomes evident

Background

The anthocyanins are highly enriched in eggplants (Solanum melongena L.) with purple peel. However, our previous study showed that anthocyanins biosynthesis in eggplant cultivar ‘Lanshan Hexian’ was completely regulated by light and color becomes evident at most 2 days after exposure to light. In the present investigation, transcriptome study was made to explore the underlying molecular mechanisms of light-induced anthocyanin biosynthesis in eggplant (Solanum melongena L.) before color becomes evident.

Results

RNA-Seq was performed for four time points (0, 0.5, 4 and 8 h after bags removal) where concerted changes happened. A total of 32,630 genes or transcripts were obtained by transcriptome sequencing, from which 1956 differentially expressed genes (DEGs) were found. Gene Ontology analysis showed that the 1956 DEGs covered a wide range of cellular components, molecular functions and biological processes. All the DEGs were further divided into 26 clusters based on their distinct expression patterns. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis found out 24 structural anthocyanin biosynthesis genes which distributing in seven clusters. In addition, 102 transcription factors, which exhibited highly dynamic changes in response to light, were found in the seven clusters. Three photoreceptors, UV Resistance Locus 8 (UVR8), Cryptochrome 3 (CRY3) and UVR3, were identified as DEGs. The light signal transduction elements, COP1 and two SPAs, might be responsible for anthocyanin biosynthesis regulation.

Conclusion

Based on the transcriptome data, the anthocyanin biosynthesis structural genes, transcription factors, photoreceptors and light signal transduction elements were quickly screened which may act as the key regulatory factors in anthocyanin biosynthesis pathway. By comparing the transcriptome data with our previous studies, 869 genes were confirmed to participate in the light-induced anthocyanin biosynthesis. These results expand our knowledge of light-induced anthocyanin biosynthesis in plants, which allowing for fruit coloration to be improved under low-light conditions in future.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4587-z) contains supplementary material, which is available to authorized users.

Concentration of phenolic compounds is increased in lettuce grown under high light intensity and elevated CO2

The present study was focused on lettuce, a widely consumed leafy vegetable for the large number of healthy phenolic compounds. Two differently-pigmented lettuce cultivars, i.e. an acyanic-green leaf cv. and an anthocyanic-red one, were grown under high light intensity or elevated CO2 or both in order to evaluate how environmental conditions may affect the production of secondary phenolic metabolites and, thus, lettuce quality. Mild light stress imposed for a short time under ambient or elevated CO2 concentration increased phenolics compounds as well as antioxidant capacity in both lettuce cvs, indicating how the cultivation practice could enhance the health-promoting benefits of lettuce. The phenolic profile depended on pigmentation and the anthocyanic-red cv. always maintained a higher phenolic amount as well as antioxidant capacity than the acyanic-green one. In particular, quercetin, quercetin-3-O-glucuronide, kaempferol, quercitrin and rutin accumulated under high light or high CO2 in the anthocyanic-red cv., whereas cyanidin derivatives were responsive to mild light stress, both at ambient and elevated CO2. In both cvs total free and conjugated phenolic acids maintained higher values under all altered environmental conditions, whereas luteolin reached significant amounts when both stresses were administered together, indicating, in this last case, that the enzymatic regulation of the flavonoid synthesis could be differently affected, the synthesis of flavones being favored.

Combined transcriptomic and proteomic analysis constructs a new model for light-induced anthocyanin biosynthesis in eggplant (Solanum melongena L.)

Light is a key environmental factor affecting anthocyanin biosynthesis. Our previous study demonstrated that "Lanshan Hexian" is a light-sensitive eggplant cultivar, but its regulatory mechanism is unknown. Here, delphinidin-3-[4-(cis-p-coumaroyl)-rhamnosyl-glucopyranoside]-5-glucopyranoside and delphinidin-3-[4-(trans-p-coumaroyl)-rhamnosyl-glucopyranoside]-5-glucopyranoside were identified as the main anthocyanin components in Lanshan Hexian by ultra-performance liquid chromatography-tandem mass spectrometry. Three time points of anthocyanin accumulation, including the start point (0 day), fastest point (5 days), and highest point (12 day), were investigated by using ribonucleic acid sequencing and iTRAQ technology. The corresponding correlation coefficients of differentially expressed genes, and differentially expressed proteins were 0.6936, 0.2332, and 0.6672. Anthocyanin biosynthesis was a significantly enriched pathway, and CHI, F3H, 3GT, 5GT, and HY5 were regulated at both transcriptional and translational levels. Moreover, some transcription factors and photoreceptors may participate in light-induced anthocyanin biosynthesis like the known transcription factors MYB113 and TT8. The transient expression assay indicated that SmMYB35, SmMYB44, and a SmMYB86 isoform might involve in the light-induced anthocyanin biosynthesis pathway. Finally, a regulatory model for light-induced anthocyanin biosynthesis in eggplant was constructed. Our work provides a new direction for the study of the molecular mechanisms of light-induced anthocyanin biosynthesis in eggplant.

Effects of UV-C Light Exposure and Refrigeration on Phenolic and Antioxidant Profiles of Subtropical Fruits (Litchi, Longan, and Rambutan) in Different Fruit Forms

The objectives of this study were to investigate how UV-C irradiation and refrigeration affect shelf-life and antioxidant level of litchi, longan, and rambutan. Three forms (whole, dehulled, and destoned) of fresh fruits were treated by refrigeration and UV-C irradiations. After processing, deterioration rate, phenolics compounds, and antioxidant capacity were quantified. The deterioration rate was recorded as decay index. The results showed that both refrigeration and UV-C exposure extended the shelf-life of the fruits. The refrigeration enriched antioxidant levels of litchi but caused nutritional degradation in longan and rambutan; UV-C radiation enriched litchi antioxidant contents but was related to reduction of antioxidant capacity in longan and rambutan. Removing hulls and stones was associated with the decrease of antioxidants in litchi. The effects on antioxidant levels varied from fruit to fruit, resulting from hormesis phenomenon. The change of phytochemical levels was hypothesized as an accumulative process. The effects of fruit forms were not consistent in different fruits, which could be multifactorially influenced.

Evaluation of Methanol Induced Free Radicals in Mice Liver

Methanol induced oxidative stress (OS) models in mice were successfully established and evaluated by the electron paramagnetic resonance (EPR) spin trapping technique. The capacity for removal of reactive oxygen species (ROS) free radicals by rhubarb and vitamin C (Vc) as candidate materials was also investigated. EPR was employed to determine the free radicals generated from a spin trapping agent, α-phenyl-N-tert-butylnitrone (PBN), that reacted with the ROS. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX), and the level of malondialdehyde (MDA) were also evaluated by enzyme assays. The results indicated that methanol clearly promoted the generation of ROS free radicals in the liver of mice. The activity of SOD and GSH-PX was reduced significantly, although the level of MDA was increased as a result of the harmful effect of methanol. In addition, rhubarb and Vc exhibited a protective effect on the mice liver under acute OS.

Hydrogen peroxide, nitric oxide and UV RESISTANCE LOCUS8 interact to mediate UV-B-induced anthocyanin biosynthesis in radish sprouts

The cross talk among hydrogen peroxide (H₂O₂), nitric oxide (NO) and UV RESISTANCE LOCUS8 (UVR8) in UV-B-induced anthocyanin accumulation in the hypocotyls of radish sprouts was investigated. The results showed that UV-B irradiation significantly increased the anthocyanin accumulation and the expression of UVR8, and a similar trend appeared in radish sprouts subjected to cadmium, chilling and salt stresses regardless of light source. However, these responses disappeared under dark exposure. These results suggest that abiotic stress-induced anthocyanin accumulation and UVR8 expression were light-dependent. Moreover, abiotic stresses all enhanced the production of H₂O₂ and exogenous H₂O₂ addition significantly increased the anthocyanin concentration and UVR8 transcription, while these increases were severely inhibited by addition of dimethylthiourea (DMTU, a chemical trap for H₂O₂). It seems to suggest that H₂O₂ played an important role in the anthocyanin biosynthesis. Furthermore, addition of 0.5 mM sodium nitroprusside (SNP, a NO-releasing compound) substantially induced the anthocyanin accumulation, and H₂O₂-induced anthocyanin accumulation and UVR8 expression were significantly suppressed by co-treatment with 2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl (PTIO, a NO scavenger), which was parallel with the expression of anthocyanin biosynthesis-related transcription factors and structural genes. All these results demonstrate that both H₂O₂ and NO are involved in UV-B-induced anthocyanin accumulation, and there is a crosstalk between them as well as a classical UVR8 pathway.