At elevated concentrations (10 g dm -3 ), a difference in the effect of QASs with L-asparaginate and L-alaninate anions was observed. The addition of 1Asp-4Asp continued to stimulate white mustard root growth up to 79% compared to the control, although it did not stimulate shoot elongation. In contrast, for compounds 1Ala-3Ala an inhibition of root (up to -43%) and shoot growth (up to -28%) was observed. Conversely, the addition of 4Ala at 10 g dm -3 resulted in a 95% and 29% increase in root and stem length, respectively. The observed phenomenon can be explained by the fact that L-alanine in high concentrations can cause phytotoxic effects in some dicotyledonous plants .