Effect of (+) and (–) Usnic Acid on Physiological, Biochemical, and Cytological Characteristics of Allium fistulosum Seeds

The effect of (+) and (–)-usnic acid (UA) on the physiological, biochemical, and cytological characteristics of Allium fistulosum L. seedlings was studied. It was shown that germination of seeds in the medium supplemented with both enantiomers of UA at concentrations of 62.5–1000 μM led to a decrease in laboratory germination, an inhibition of growth processes, a slowing of the mitotic activity of root meristems, and tissue depigmentation. A dose-dependent increase in the frequency of chromosomal aberrations and the degree of damage to nuclear DNA in cells was shown, which indicates the potentially genotoxic and mutagenic effect of the studied UA enantiomers. However, (–)-UA induced a greater number of atypical DNA comets than the (+)-enantiomer, which may indicate its stronger effect on DNA fragmentation in cells. An increase in the activity of antioxidant enzymes and a decrease in the content of flavonoids were observed under the action of both UA enantiomers against the background of the accumulation of lipid peroxidation products in seedlings’ cells, which indicates the development of oxidative stress. At the same time, no significant differences between the activity of (+) and (–)-UAs at the level of physiological and biochemical parameters of seedlings were revealed.