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Effect of UV-B rays (280-320 nm) on photosynthetic electron transport and production of phenolic compounds in tea ( Camellia sinensis L.) callus culture grown in white light was investigated. When white light was supplemented with UV radiation, the culture growth was retarded and morphological characteristics were modified. These conditions promoted the formation of chlorophyll-bearing cells and altered the ability of cultured cells to accumulate phenolic compounds, including flavans specific to Camellia sinensis . By the end of the culturing cycle (on the 45th day), the total content of phenolic compounds in the culture grown under supplementary UV irradiation was almost 1.5 times higher than in the control culture. The UV rays greatly stimulated photosystem II (PSII) activity in phototrophic cells of the callus culture, which was indicated by a large increase in the ratio of variable chlorophyll fluorescence to maximal fluorescence. This ratio was as low as 0.19 in cells cultured in white light and increased to 0.53 in the cell culture grown under white and UV light. The kinetics of dark relaxation of chlorophyll variable fluorescence, related to reoxidation of PSII primary acceptor, contained either two or three components, depending on the absence or presence of UV radiation, respectively. An artificial electron acceptor of PSI, methyl viologen modified the kinetics of dark decay of chlorophyll variable fluorescence in a characteristic manner, implying that photosynthetic electron transport was mediated by PSI and PSII in both treatments (culturing in white light with and without UV-B). It is concluded that stimulatory effect of UV rays on the parameters examined in phototrophic regions of Camellia tissue culture is determined by photoexcitation of a regulatory pigment that absorbs quanta in blue and long-wave UV spectral regions.

Soil organic matter (SOM) is the largest reservoir of organic carbon in the biosphere. However, little is known about the processes of its formation at the pre‐vascular stage. Lichens are among the pioneer colonizers on mineral substrates and are possible early land flora. This study is the first report on the identification and quantification of water‐soluble phenolic compounds (PCs), potential precursors of humic substances, in epigeyic lichens from two systematic groups. Results show (Folin–Denis assay) that cyanobiont‐containing lichens (order Peltigerales) possess three to five times more total soluble PCs than Lecanoralean lichens (Cladonia, Cetraria spp.) and mosses. Soluble PCs in lichens occur in the conjugated form. Alkali‐hydrolysable compounds (esters) predominate over acid‐hydrolysable compounds (glycosides). Phenolic complexes with N‐containing compounds or reducing sugars, or both, have been identified by thin layer chromatography (TLC). Benzoic acid derivatives were most common among PCs, detected in lichens by reversed‐phase high‐pressure liquid chromatography (RP‐HPLC). Phenolic acids occur in the order (μg 100 g−1): p‐hydroxybenzoic acid (327–1,007) > syringic acid (87–361) > salycilic acid (135–210) > vanillic acid (12–19) (Peltigeralean lichens); salicylic acid (53–102) > p‐hydroxybenzoic acid (45–54) > caffeic acid (29) > syringic acid (18) > vanillic acid (9–13) (Lecanoralean lichens). Protocatechuic, caffeic and p‐coumaric acids were rare; ferulic acid was not detected. Syringyl and vanillyl aldehydes and ketones occur in much larger amounts than acids. Methoxy‐substituted and ortho‐substituted phenols, detected in lichens, are known for their high reactivity in soils under lignified vegetation, suggesting their important roles in SOM formation under a cryptogam cover. Highlights Phenolic composition of SOM and humification processes at pre‐vascular stage are largely overlooked Soluble phenolic acids, aldehydes and ketones are quantified in lichens for the first time Lichens are depleted in phenylpropanoids and enriched in syringyl structures and monophenols Lichen‐derived phenolic compounds are potential precursors of humic substances under cryptogam cover

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Late blight is one of the most economically important diseases affecting potato and causing a significant loss in yield. The development of transgenic potato plants with enhanced resistance to infection by Phytophthora infestans may represent a possible approach to solving this issue. A comparative study of the leaf response in control potato plants (S.tuberosum L. cultivar Skoroplodnyi), control transgenic plants expressing the reporter gene of thermostable lichenase (transgenic licBM3 line) and transgenic plants expressing cyanobacterial hybrid genes ∆9-acyl-lipid desaturase (transgenic desC lines) and ∆12-acyl-lipid desaturase (transgenic desA lines) to infection with P. infestans has been performed. The expression of desaturase genes in potato plants enhanced their tolerance to potato late blight agents as compared with the control. The lipid peroxidation level raised in the leaves of the control and transgenic desA plants on third day after inoculation with P. infestans zoospores and remained the same in the transgenic desC plants. The number of total phenolic compounds was increased as early as on the second day after infection in all studied variants and continued to remain the same, except for transgenic desC plants. Accumulation of flavonoids, the main components of the potato leaf phenolic complex, raised on the second day in all studied variants, remained unchanged on the third day in the control plants and decreased in most transgenic plants expressing desaturase genes. The results obtained in our study demonstrate that the expression of genes of Δ9- and Δ12-acyl-lipid desaturases in potato plants enhanced their resistance to P. infestans as compared with the control non-transgenic plants due to concomitant accumulation of phenolic compounds, including flavonoids, in the leaves. All these changes were more pronounced in transgenic desC plants, which indicates that the Δ9-acyllipid desaturase gene appears to be a potential inducer of the production of biological antioxidants in plant cells.

Tea plants (Camellia sinensis L.) are phenol-accumulating crops that are widely used for public health. The healing effect of tea leaf products is due to the biosynthesis of such phenolic compounds (PCs) as flavans, which have P-vitamin capillary-strengthening activity. Due to their limited habitat and the value of their specialized metabolites of a phenolic nature, a promising approach is to establish in vitro cultures from them that retain the ability to form PCs, which is characteristic of ex vivo tea plants. The aim of this study was to investigate the effect of exogenic H2O2 (0.01 mM; 0.1 mM; 1 mM) on the growth, morphology, degree of stress response, and accumulation of various phenolic compounds in tea plant callus cultures of different ages (24 or 36 days) grown under different cultivation conditions (darkness or light). According to the results obtained, the H2O2 effect on tea callus cultures of different ages did not cause changes in their morphophysiological characteristics, both after 2 h of exposure (rapid response of callus culture, RRCC) and after 48 h (delayed response of callus culture, DRCC). The determination of the malondialdehyde (MDA) content, which serves as an indicator of changes in the level of lipid peroxidation (LPO) and the presence of stress responses in plant cells, indicated either its maintenance at the control level, a decrease, or an increase. All these effects depended on the growth conditions of the tea callus cultures (darkness or light), their age, the duration of exposure (rapid or delayed response), and the H2O2 concentration. Similar trends were noted for the total content of PCs as well as the amount of flavans, proanthocyanidins (soluble and insoluble forms), and lignin. The plant cell responses reflected changes in its adaptation programs, when specialized metabolites act as a target for the action of H2O2, thereby contributing to an increase in their resistance.

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