Polymetallic Stress Changes the Endogenous Status of Brassinosteroids and Reduces the Effectiveness of Photochemical Reactions Photosystem II in Barley Plants

The effect of polymetallic stress (Mn 2+ , Cd 2+ , Cu 2+ , Ni 2+ , Zn 2+ , Pb 2+ , and Al 3+ ) of different duration and intensity on the endogenous brassinosteroids (BS) content and photochemical activity of photosystem II in barley plants was studied. The content of steroid hormones was determined by a two-stage enzyme immunoassay. It was established for the first time that barley plants responded to polymetallic stress by changing the endogenous content of various phytosteroid groups (24S-methylBS, 24-epiBS, 28-homoBS, B-lactoneBS, and 6-ketoBS). It was shown that the stress-dependent dynamics of changes in the endogenous content of various BS groups is characterized by organ specificity and is determined by the age of plants, the intensity of the acting stressor, and the specificity of brassinosteroids. The observed changes in the endogenous status of BS in barley plants under polymetallic stress are accompanied by inhibition of growth processes, a decrease in the content of the main photosynthetic pigments, and a slight decrease in the efficiency of photochemical processes in PS II ( F v / F m , ETR, qN , and NPQ ). Considering the multifunctional stress-protective effect of brassinosteroids, it is assumed that the change in the endogenous status of BS against the background of polymetallic pollution is adaptive and allows minimizing the damaging effects of toxic heavy metals and aluminum.