Human skin is constantly exposed to damaging ultraviolet radiation (UVR), which induces a number of acute and chronic disorders. To reduce the risk of UV-induced skin injury, people apply an additional external protection in the form of cosmetic products containing sunscreens. Nowadays, because of the use of some chemical filters raises a lot of controversies, research focuses on exploring novel, fully safe and highly efficient natural UV-absorbing compounds that could be used as active ingredients in sun care products. A promising alternative is the application of multifunctional mycosporine-like amino acids (MAAs), which can effectively compete with commercially available filters. Here, we outline a complete characterization of these compounds and discuss their enormous biotechnological potential with special emphasis on their use as sunscreens, activators of cells proliferation, anti-cancer agents, anti-photoaging molecules, stimulators of skin renewal, and functional ingredients of UV-protective biomaterials.

Impact of macrophyte Lemna trisulca on the growth rate and synthesis of cylindrospermopsin (CYN) by cyanobacterium Raphidiopsis raciborskii was determined. The presence of L. trisulca inhibited the biomass accumulation of the cyanobacterium by 25% compared to the control during co-cultivation. The simultaneous cultivation of these organisms slightly affected the inhibition of macrophyte growth rate by 5.5% compared to the control. However, no morphological changes of L. trisulca after incubation with cyanobacteria were observed. It was also shown that the long-term (35 days) co-cultivation of R. raciborskii and L. trisulca led to a decrease in CYN concentration in media and cyanobacterial cells by 32 and 38%, respectively, compared to the values obtained for independent cultivation of cyanobacterium. Excessive absorption of phosphate ions by L. trisulca from the medium compared to nitrate ions led to a significant increase in the nitrate:phosphate ratio in the media, which inhibits the development of cyanobacterium. The obtained results indicate that L. trisulca in the natural environment may affect the physiology of cyanobacteria. The presented study is the first assessment of the allelopathic interaction of macrophyte and R. raciborskii.

The increase in frequency and prevalence of cylindrospermopsin (CYN)-producing cyanobacteria blooms have become a growing problem worldwide. Therefore, the long-term effects of CYN on the physiological processes of the macrophyte, Lemna trisulca, were examined. During a 5-day exposure to a range of CYN concentrations (0.5, 1 and 5 μg ml⁻¹), the low levels of stress experienced by L. trisulca stimulated its growth rate and photosynthesis and led to an increase in the synthesis of photosynthetic pigments. In turn, it was shown that a 3-week exposure to the highest tested CYN concentration (5 μg ml⁻¹) resulted in the inhibition of biomass accumulation (by 7.6%) compared with that of the control plants, but necrosis and chlorosis were not observed. A negative correlation with the concentration of carotenoids was also observed, which may suggest that the antioxidant mechanisms of L. trisulca are effective only up to a certain CYN concentration. An increase in protein content in the tissues of macrophytes treated with concentrations of CYN ranging from 0.5 to 5 μg ml⁻¹ indicates that the toxin did not inhibit protein synthesis but increased the metabolism of L. trisulca, potentially to provide energy for defence. The toxin also affects the homeostasis of mineral ions in cells. This is the first description of the physiological response of L. trisulca to the long-term effects of a wide range of CYN concentrations.

Cladonia arbuscula in its environmental niches is regularly affected by daily and annual variations in solar radiation. Mycosporine-glutamicol, Myc-Glu(OH), which it synthesizes, may act as a significant cellular UV-protector. Therefore, we studied this compound concentration in lichen thalli concerning seasonal changes and increased exposure to UV-B and photosynthetically active radiation (PAR) with/without simultaneous CO₂ deprivation. Myc-Glu(OH) occurred year-round and exhibited a strong seasonality. The most crucial role in the control of its synthesis played UV-B radiation, although its high concentration was also found after PAR irradiation at 1000 µmol m⁻² s⁻¹. As PAR intensity increased to 2000 µmol m⁻² s⁻¹, the rate of Myc-Glu(OH) synthesis slowed down. In turn, under dark/PAR irradiation with simultaneous deprivation of CO₂ in the atmosphere surrounding C. arbuscula and during darkness with continuous access to atmospheric CO₂, its production was insignificant. Obtained data confirmed that Myc-Glu(OH) plays an important role in protecting C. arbuscula from UV damage and favours its adaptation to environmental stress in its natural habitat. They also suggest that its synthesis is a synergism of multiple factors. Consequently, further studies should focus on their evaluation and the identification of a lichen partner actively involved in Myc-Glu(OH) biogenesis.