Hormesis and paradoxical effects of pea (Pisum sativum L.) parameters upon exposure to formaldehyde in a wide range of doses.

Formaldehyde is a widespread pollutant of soil near roads including agricultural lands. Non-monotonic changes (hormesis and paradoxical effects) in chlorophyll (Ch) and carotenoid (Car) contents, the lipid peroxidation (LP) rate in plant leaves and growth parameters (GP) of plants can be caused by various pollutants. Hormesis is a biphasic dose-response phenomenon, characterised by low-dose stimulation and high-dose inhibition. The remaining types of non-monotonic responses are classified as paradoxical effects. While most authors who have studied formaldehyde and plants considered gaseous exposure to shoots, the effect of this pollutant in soil solution has been poorly examined. Thus, we studied the non-monotonic changes in Ch and Car contents, LP rate and GP in pea (Pisum sativum L.) upon exposure to formaldehyde in solution, at a wide range of sublethal concentrations from 0.063 × 10-2 to 0.16 g L-1. With formaldehyde exposure, LP and Ch contents had paradoxical effects (triphasic and multiphase changes, accordingly), while Car level did not change and GP exhibited a hormetic response. The date showed that pea parameters display diverse types of non-monotonic responses upon exposure to the same formaldehyde concentrations. High pollutant concentrations (0.08-0.16 g L-1) increased LP and significantly decreased GP (to 2.3-2.5 times compared to the control), while the Ch content was increased. Lower concentrations (<0.08 g L-1) caused a moderate deviation in all parameters from the control (not more than 62%) for hormesis and paradoxical effects.