Flavonoids are small molecular secondary metabolites synthesized by plants with various biological activities. Due to their physical and biochemical properties, they are capable of participating in plants’ interactions with other organisms (microorganisms, animals and other plants) and their reactions to environmental stresses. The majority of their functions result from their strong antioxidative properties. Although an increasing number of studies focus on the application of flavonoids in medicine or the food industry, their relevance for the plants themselves also deserves extensive investigations. This review summarizes the current knowledge on the functions of flavonoids in the physiology of plants and their relations with the environment.

Phenolic compounds constitute a group of secondary metabolites which have important functions in plants. Besides the beneficial effects on the plant host, phenolic metabolites (polyphenols) exhibit a series of biological properties that influence the human in a health-promoting manner. Evidence suggests that people can benefit from plant phenolics obtained either by the diet or through skin application, because they can alleviate symptoms and inhibit the development of various skin disorders. Due to their natural origin and low toxicity, phenolic compounds are a promising tool in eliminating the causes and effects of skin aging, skin diseases, and skin damage, including wounds and burns. Polyphenols also act protectively and help prevent or attenuate the progression of certain skin disorders, both embarrassing minor problems (e.g., wrinkles, acne) or serious, potentially life-threatening diseases such as cancer. This paper reviews the latest reports on the potential therapy of skin disorders through treatment with phenolic compounds, considering mostly a single specific compound or a combination of compounds in a plant extract.

Summary: Fructose 2,6‐bisphosphate (fru‐2,6‐P₂) is a signalling metabolite that regulates photosynthetic carbon partitioning in plants. The content of fru‐2,6‐P₂ in Arabidopsis leaves varied in response to photosynthetic activity with an abrupt decrease at the start of the photoperiod, gradual increase through the day, and modest decrease at the start of the dark period. In Arabidopsis suspension cells, fru‐2,6‐P₂ content increased in response to an unknown signal upon transfer to fresh culture medium. This increase was blocked by either 2‐deoxyglucose or the protein phosphatase inhibitor, calyculin A, and the effects of calyculin A were counteracted by the general protein kinase inhibitor K252a. The changes in fru‐2,6‐P₂ at the start of dark period in leaves and in the cell experiments generally paralleled changes in nitrate reductase (NR) activity. NR is inhibited by protein phosphorylation and binding to 14‐3‐3 proteins, raising the question of whether fructose‐6‐phosphate,2‐kinase/fructose‐2,6‐bisphosphatase protein from Arabidopsis thaliana (AtF2KP), which both generates and hydrolyses fru‐2,6‐P₂, is also regulated by phosphorylation and 14‐3‐3s. Consistent with this hypothesis, AtF2KP and NR from Arabidopsis cell extracts bound to a 14‐3‐3 column, and were eluted specifically by a synthetic 14‐3‐3‐binding phosphopeptide (ARAApSAPA). 14‐3‐3s co‐precipitated with recombinant glutathione S‐transferase (GST)‐AtF2KP that had been incubated with Arabidopsis cell extracts in the presence of Mg‐ATP. 14‐3‐3s bound directly to GST‐AtF2KP that had been phosphorylated on Ser220 (SLSASGpSFR) and Ser303 (RLVKSLpSASSF) by recombinant Arabidopsis calcium‐dependent protein kinase isoform 3 (CPK3), or on Ser303 by rat liver mammalian AMP‐activated protein kinase (AMPK; homologue of plant SNF‐1 related protein kinases (SnRKs)) or an Arabidopsis cell extract. We have failed to find any direct effect of 14‐3‐3s on the F2KP activity in vitro to date. Nevertheless, our findings indicate the possibility that 14‐3‐3 binding to SnRK1‐phosphorylated sites on NR and F2KP may regulate both nitrate assimilation and sucrose/starch partitioning in leaves.

Diet bioactive components, in the concept of nutrigenetics and nutrigenomics, consist of food constituents, which can transfer information from the external environment and influence gene expression in the cell and thus the function of the whole organism. It is crucial to regard food not only as the source of energy and basic nutriments, crucial for living and organism development, but also as the factor influencing health/disease, biochemical mechanisms, and activation of biochemical pathways. Bioactive components of the diet regulate gene expression through changes in the chromatin structure (including DNA methylation and histone modification), non-coding RNA, activation of transcription factors by signalling cascades, or direct ligand binding to the nuclear receptors. Analysis of interactions between diet components and human genome structure and gene activity is a modern approach that will help to better understand these relations and will allow designing dietary guidances, which can help maintain good health.