Effect of pretreatment of barley seedlings with different salts on the level of UV-B induced and UV-B absorbing compounds

The relationship between the level of UV-B-induced and/or UV-B-absorbing compounds and stress tolerance of barley seedlings (Hordeum vulgare L. cv. Alfa) was investigated. A physiological response to UV-B irradiation was evaluated by measuring the oxygen evolution rate and chlorophyll fluorescence. UV-B irradiation led to an increase of the amount of UV-B absorbing compounds, including flavonoids, measured in acidified methanol extract at 300 nm and of UV-B induced compounds, with maximum absorbance at 438 nm, extracted in 0.1% trichloracetic acid. The content of free proline, malondialdehide and H2O2 increased as a result of 4 days treatment with 150 mM NaCl, KCl or NaNO3. Salt pretreatment resulted in considerable decrease of the level of UV-induced and UV-B absorbing compounds measured 24 h after UV-B irradiation. In the meantime chlorophyll fluorescence parameters and oxygen evolution in salt pretreated seedlings were less affected by UV-B in comparison to the control. Damaging effect of UV-B measured by the MDA and H2O2 generation and electron transport activity corresponded to the increased levels of UV-B induced and UV-B absorbing compounds. We do not necessarily exclude UV-inducing compounds from an important role in overall UV-B protection but the data presented here showed that the accumulation of these compounds could be a consequence of stress-induced damage to the cells and probably they may serve as stress markers. (c) 2005 Elsevier B.V. All rights reserved.