Analysis of young white mustard plants revealed an interesting effect of the new quinine-based QASs on the growth rate of roots and shoots (Fig. ). At a concentration of 1 g dm -3 , the tested salts caused an increase in shoot length by 31-100% compared to the control, while roots were elongated by 24-158%. 4Asp and 4Ala had the strongest stimulating effect on root growth, and in their case the differences in white mustard root length (152% and 158%, respectively) were statistically significant compared to the control. Regarding the shoot elongation, a significant difference to the control was also recorded for 4Asp (100% increase). The beneficial effect of 4Asp and 4Ala may be due to the high hydrophilicity of these compounds (log KOW < -1), which positively influences the bioavailability of quinine-based cation in the soil. At the same time, it should be remembered that the cation and anion of QASs behave differently in the soil and their effects on plants should be considered separately . Given that 4Br with the same cation stimulated root and shoot growth to a lesser extent, it can be predicted that the plant growth-stimulating effect observed for 4Asp and 4Ala is a product of the beneficial effect of the 1-(2-hydroxyethyl)quinium cation and the enhancement of metabolism caused by exogenous application of proteinogenic amino acids . It should also be emphasized that the growth-stimulating activity of quinine in terrestrial plants has not yet been studied in detail, and thus further research of this phenomenon is recommended.