Allelopathy Journal

The effects of (+)—usnic acid (2,6—diacyl—7,9—dihydroxy—8,9b—dimethyl-odibenzofuran—1,3 (2H,9bH)—dione; UA) stress factor, a secondary metabolite in lichens, on several biochemical and physiological processes in tomato (Lycopersicon esculentum Mill.) roots were investigated. The tomato plants were cultivated for 21 days (10 to 31 days after germination) in Hoagland's nutrient solution containing 0 to 30 μM of (+)—UA. Some experiments were also done on control roots, incubating for short-term (5.0 h) in solution containing different concentrations of (+)—UA. The effects observed depended on the concentration of (+)—UA and the exposure time. In roots incubated for 5.0 h in solution containing 30 μM (+)—UA, electrolyte leakage was increased by 2 times, plasma membrane injury was about 10%, the leakage of inorganic ions was up to 3.1 times higher than in control, while, ion uptake was reduced by 54%. Certain effects occurred only in plants cultivated for long-term (for 21 days) in solution containing (+)—UA; lipid peroxidation was increased by 58%, proline content was up to 33 times of control value, the activities of antioxidative enzymes were increased (catalase by 58%) and plasma membrane H⁺-ATPase activity decreased by 59% than control. Thus UA exerts a multidirectional toxic effects on many physiological processes, which could mutually influence each other.