Screening the Key Region of Sunlight Regulating the Flavonoid Profiles of Young Shoots in Tea Plants (Camellia sinensis L.) Based on a Field Experiment.

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars ('Longjing 43', 'Zhongming 192', 'Wanghai 1', 'Jingning 1' and 'Zhonghuang 2') to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes.

Flavonoid Glycosides in Brassica Species Respond to UV-B Depending on Exposure Time and Adaptation Time.

Recently, there have been efforts to use ultraviolet-B radiation (UV-B) as a biotechnological tool in greenhouses. Leafy Brassica species are mainly considered for their ability to synthesize glucosinolates and are valued as baby salads. They also have a remarkable concentration of chemically diverse flavonoid glycosides. In this study, the effect of short-term UV-B radiation at the end of the production cycle was investigated without affecting plant growth. The aim was to verify which exposure and adaptation time was suitable and needs to be further investigated to use UV as a biotechnological tool in greenhouse production of Brassica species. It is possible to modify the flavonoid glycoside profile of leafy Brassica species by increasing compounds that appear to have potentially high antioxidant activity. Exemplarily, the present experiment shows that kaempferol glycosides may be preferred over quercetin glycosides in response to UV-B in Brassica rapa ssp. chinensis, for example, whereas other species appear to prefer quercetin glycosides over kaempferol glycosides, such as Brassica oleracea var. sabellica or Brassica carinata. However, the response to short-term UV-B treatment is species-specific and conclusions on exposure and adaptation time cannot be unified but must be drawn separately for each species.

Synthesis of new UV-B light absorbents: (Acetylphenyl)glycosides with antioxidant activities.

m-Acetylphenyl-beta-d-glucopyranosides and m-acetylphenyl-alpha/beta-d-mannopyranosides were synthesized by the Koenigs-Knorr, Mitsunobu, and Helferich reactions as key glycosylation reactions, respectively. Their spectroscopic properties and antioxidative activities were characterized as potential ultraviolet B-ray absorbents.

Radioresistance of Salmonella species and Listeria monocytogenes on minimally processed arugula (Eruca sativa Mill.): effect of irradiation on flavonoid content and acceptability of irradiated produce.

This work studied the radiation resistance of Listeria monocytogenes and Salmonella species and the effect of irradiation on leaf flavonoid content and sensory acceptability of minimally processed arugula. Immersion in ozone-treated water reduced the analyzed microorganisms by 1 log. L. monocytogenes and Salmonella were not isolated from samples. Samples of this vegetable were inoculated with a cocktail of Salmonella spp. and L. monocytogenes and exposed to gamma irradiation. D10 values for Salmonella ranged from 0.16 to 0.19 kGy and for L. monocytogenes from 0.37 to 0.48 kGy. Kaempferol glycoside levels were 4 and ca. 3 times higher in samples exposed to 1 and 2 kGy, respectively, than in control samples. An increase in quercetin glycoside was also observed mainly in samples exposed to 1 kGy. In sensory evaluation, arugula had good acceptability, even after exposure to 2 and 4 kGy. These results indicate that irradiation has potential as a practical processing step to improve the safety of arugula.

Phosphodiester and N-glycosidic bond cleavage in DNA induced by 4-15 eV electrons.

Thin molecular films of the short single strand of DNA, GCAT, were bombarded under vacuum by electrons with energies between 4 and 15 eV. Ex vacuo analysis by high-pressure liquid chromatography of the samples exposed to the electron beam revealed the formation of a multitude of products. Among these, 12 fragments of GCAT were identified by comparison with reference compounds and their yields were measured as a function of electron energy. For all energies, scission of the backbone gave nonmodified fragments containing a terminal phosphate, with negligible amounts of fragments without the phosphate group. This indicates that phosphodiester bond cleavage by 4-15 eV electrons involves cleavage of the C-O bond rather than the P-O bond. The yield functions exhibit maxima at 6 and 10-12 eV, which are interpreted as due to the formation of transient anions leading to fragmentation. Below 15 eV, these resonances dominate bond dissociation processes. All four nonmodified bases are released from the tetramer, by cleavage of the N-glycosidic bond, which occurs principally via the formation of core-excited resonances located around 6 and 10 eV. The formation of the other nonmodified products leading to cleavage of the phosphodiester bond is suggested to occur principally via two different mechanisms: (1) the formation of a core-excited resonance on the phosphate unit followed by dissociation of the transient anion and (2) dissociation of the CO bond of the phosphate group formed by resonance electron transfer from the bases. In each case, phosphodiester bond cleavage leads chiefly to the formation of stable phosphate anions and sugar radicals with minimal amounts of alkoxyl anions and phosphoryl radicals.

Homolytic cleavage of the O-glycoside bond in carbohydrates: a steady-state radiolysis study.

The formation of products resulting from the O-glycoside bond cleavage following radiolysis of aqueous solutions of methyl-alpha-D-glucopyranoside (I), 3-O-methyl-alpha-D-glucopyranose (II), maltose, lactose, gentiobiose and cellobiose were studied. Radiation-induced destruction yields were also determined for dextran, laminarin and trimethylcelulose upon irradiation of their aqueous solutions. Oxygen, quinones and compounds capable of forming quinoid structures were found to inhibit radiation-induced homolytic destruction processes taking place in glycosides, di- and polysaccharides. The data obtained in this study enabled the authors to demonstrate an important role played by the fragmentation reaction of C-2 radicals which were generated from the starting substances in the formation of final radiolysis products.

Evidence for glycosidic bond rotation in a nucleobase peroxyl radical and its effect on tandem lesion formation.

Nucleobase peroxyl radicals are the major reactive intermediates formed in DNA when the biopolymer is exposed to gamma-radiolysis under aerobic conditions. The major reaction pathways for the peroxyl radical (1) derived from 5,6-dihydro-2'-deoxyuridin-6-yl involve pi-bond addition to or hydrogen atom abstraction from the adjacent nucleotides to produce tandem lesions. The ability to independently generate 1 at a defined site in DNA enabled us to probe its reactivity by varying the local DNA structure. The effect of DNA structure variation reveals that 1 reacts from its syn- and anti-conformations in competition with trapping by thiol. These experiments also reveal that tandem lesions will be produced as a mixture of diastereomers, which could impact their biological effects.

Synthesis of lactoside glycodendrons using photoaddition and reductive amination methodologies.

Carbohydrate-based divalent and tetravalent lactoside glycodendrons were constructed in a convergent manner. The dendrons were synthesized beginning with the photoaddition of hepta-O-acetyl-1-thio-beta-lactose, in an anti-Markovnikov manner, to a bis-allyl AB2 trisaccharide to form a divalent dendron. Following two nearly quantitative deprotection steps, the divalent lactoside was coupled to another AB2 trisaccharide by reductive amination to afford a tetravalent dendron. These paucivalent compounds were characterized by NMR spectroscopy and mass spectrometry.

Glycosidic bond cleavage of thymidine by low-energy electrons.

Thymidine was exposed to low-energy electrons (LEE) as a thin solid film under a high vacuum. Nonvolatile radiation products, remaining on the irradiated surface, were analyzed by HPLC/UV and GC/MS. Here, we show that exposure of thymidine to 3-100 eV electrons gives thymine as a major product with a yield of 3.2 x 10-2 per electron (about one-third of the total decomposition of thymidine). The formation of thymine indicates that LEE induces cleavage of the glycosidic bond separating the base and sugar moieties, suggesting a nonionizing resonant process involving dissociative attachment (<15 eV). In contrast, this reaction is not very efficient by DNA base ionization and does not occur by the reaction of solvated electrons with DNA. These studies introduce a new mechanism of DNA damage involving the interaction of LEE.

Photoreaction of methyl and phenyl 4,6-O-benzylidene-2,3-dideoxy-2-C-p-tolylsulfonyl-beta-D-erythro-hex-2-enopyranosides in methanol.

The title compounds were irradiated with a high-pressure mercury lamp in methanol to give 2-C-hydroxymethyl derivatives having the gluco, altro, and allo configurations as well as an S(N)2' product. Equatorial attack of a hydroxymethyl radical slightly predominated over axial attack. During chromatographic separation on a silica gel column, partial migration of the 4,6-O-benzylidene group in the gluco and altro products occurred to yield the 3',4-O-benzylidene derivatives.

Activation of antitumor agent gilvocarcins by visible light.

Gilvocarcins that are antitumor agents are activated by low doses of visible light to induce bacteriophage lambda in Escherichia coli. This result is dependent on interaction with DNA. Gilvocarcin M, an analog without antitumor activity, failed to induce the prophage after light exposure, thus demonstrating a correlation between photosensitizing and antitumor activities. These results raise several possibilities regarding the mode of action of gilvocarcins as antitumor agents in vivo, involving light or enzymatic activating systems, which could be exploited in human cancer therapy.