Morpho-physiological reactions of gravisensitivity and adaptation to UV-radiation of the moss Bryum Caespiticiumhedw. from Antarctica

Abstract

The adaptive physiological reactions of the moss Bryum caespiticium Hedw. from Antarctica to the influence of UV radiation and gravimorphoses as a factor of adaptive plasticity, associated with environmental conditions, were studied. As a control, B. caespiticium plants were collected in the Nature Reserve “Roztochchia” (Lviv region). In investigations, we used a sterile laboratory culture of mosses grown under controlled conditions in a phytotron. Moss shoots were irradiated with UV rays generated by an ultraviolet lamp OSRAM with an intensity of 4 kW/m2, which caused 50 % inhibition of plant regeneration (ED50). Physiological parameters were determined 24 h after exposure to UV radiation. The influence of gravity on the morphological form of B. caespiticium gametophyte turf and the interaction of light and gravity in gravi-/phototropism as a manifestation of gravimorphoses adaptability were analyzed. One of the objectives was to investigate the formation of gravimorphoses as a result of the initiation of cells’ branching processes and the formation of gametophore buds and to evaluate their role in the life cycle of B. caespiticium under extreme conditions. For this, we determined the branching coefficient of the gravitropic protonema, the inclination angle of the branches and the buds’ development depending on the interaction of photo- and gravitropism, under the influence of red and blue light, and the effect of UV on gravisensitivity. The influence of physiologically active red and blue light on the branching activity and bud formation on the gravitropic protonema of the Antarctic moss B. caespiticium was investigated. It was found that red light mainly inhibited graviperception and gravitropic growth of protonemata cells, resulting in a change of the response to gravity, but initiated high branching activity and, accordingly, another morphological form of turf. After the influence of the blue light, intensive bud formation and gametophore development were observed. Thus, gravitation promoted morphological variability and changes in the functional activity of cells at the juvenile stage of the protonemata development, which is important for the survival of the moss under extreme environmental conditions. After UV irradiation the gravisensitivity of the B. caespiticium protonemata decreased. However, due to the resistance of the moss sample from Antarctica to the prolonged influence of UV rays, gravitropic growth was not completely blocked, as in plants from the Lviv region. The effect of the ultraviolet irradiation on the antioxidant activity, the content of soluble (vacuolar) and cell wall-bound fractions of UV-absorbing phenolic components, flavonoids content and their absorption spectra, as well as the amount of carotenoids and anthocyanins in B. caespiticium shoots, were determined. It was established that B. caespiticium plants from Antarctica have 1.5 times higher antioxidant activity compared to plants from the Lviv region, which confirms the high level of protection against oxidative damage. UV irradiation activates the synthesis of UV-absorbing phenolic compounds in mosses. The shoots of B. caespiticium from Antarctica defined a higher content of phenols compared to samples from the Lviv region and their significant increase under the influence of UV radiation. The content of UV-absorbing compounds bound with the cell wall was higher than the concentration of soluble phenolic compounds, both in plants from Antarctica and in samples from the Lviv region, which indicates their participation in the mechanisms of cells protection from UV radiation. It was shown that the influence of UV irradiation induced an increase of flavonoids’ content in the shoots of both samples of B. caespiticium, but for plants from Antarctica, the concentration of flavonoids after stress was 1.7 times higher than in plants from the Lviv region. The absorption spectra of flavonoids revealed flavonols rutin and quercetin and flavone luteolin in both samples of B. caespiticium, which provide effective cells absorption of UV rays. The higher content of anthocyanins and carotenoids in moss shoots from Antarctica both in the control sample and after the exposure to UV radiation promotes the protection against damage and formation of the adaptive potential.