Hormesis and paradoxical effects of wheat seedling (triticum aestivum L.) parameters upon exposure to different pollutants in a wide range of doses.

Chlorophyll and carotenoid content (ChCar), lipid peroxidation (LP) and growth parameters (GP) in plants are often used for environmental pollution estimation. However, the nonmonotonic dose-response dependences (hormesis and paradoxical effects) of these indices are insufficiently explored following exposure to different pollutants. In this experiment, we studied nonmonotonic changes in ChCar, LP, GP in wheat seedlings (Triticum aestivum L.) upon exposure to lead, cadmium, copper, manganese, formaldehyde, the herbicide glyphosate, and sodium chloride in a wide range from sublethal concentration to 10(2)-10(5) times lower concentrations. 85.7% of dose-response dependences were nonmonotonic (of these, 5.5% were hormesis and paradoxical effects comprised 94.5%). Multiphasic dependences were the most widespread type of paradoxical effect. Hormesis was a part of some multiphasic responses (i.e. paradoxical effects), which indicates a relationship between these phenomena. Sublethal pollutant concentrations significantly increased LP (to 2.0-2.4 times, except for manganese and glyphosate) and decreased GP (to 2.1-36.6 times, except for glyphosate), while ChCar was reduced insignificantly, normalized or even increased. Lower pollutant concentrations caused a moderate deviation in all parameters from the control (not more than 62%) for hormesis and paradoxical effects. The seedling parameters could have different types of nonmonotonic responses upon exposure to the same pollutant.