||Adaptation of plants to the ever-changing environment requires the integration of many endogenous ontogenic and exogenous environmental signals. Reactive oxygen and nitrogen species and phytohormones are the central components of this integration process regulating plant development and stress responses. In addition, components of the same as well as the distinct signaling pathways intensively interact among themselves. In order to gain more insight into the role of these signaling pathways in the response of barley root to stress conditions, the aim of the present project is the analysis of function of some specific signaling components in stress responses, using chemical biology, a new and powerful approaches, to unravel mechanisms of plant adaptation processes. Using small synthetic bioactive molecules for blocking the specific components of stress responses could uncover the function of physiological and biochemical processes in the toxicity and defense responses of roots to heavy metals.