Transformation of Indole-3-butyric Acid into Ionic Liquids as a Sustainable Strategy Leading to Highly Efficient Plant Growth Stimulators

Abstract

Phytohormones are chemical substances that regulate plants growth, reproductive processes, longevity, development, and even death. One of the most common representatives of this group is indole-3-butyric acid (IBA), which is widely applied in various branches of agriculture. Taking into consideration that the conversion of conventional herbicides into ionic liquids leads to the enhancement of their biological activity, we decided to implement the same strategy for selected phytohormone. Hence, we synthesized a homologous series comprising alkylated choline cations and indole-3-butyrate anions. The new biobased ionic liquids (ILs) were characterized in terms of physicochemical properties (thermal stability, phase transitions, solubility, surface activity, density, and viscosity) and susceptibility to biodegradation according to the OECD 301 F test. Subsequently, their activity as a growth stimulator was evaluated for butterhead lettuce (Lactuca sativa L.) as a test plant. Additionally, the nutrient assimilation by the test plants was analyzed. The study revealed that the IL containing cations with octyl groups, at the optimal concentration of 0.5 ppm, enhanced lettuce biomass production by approximately 21% compared to that of the control. Moreover, the lettuce was enriched with valuable micro- and macroelements, such as P, K, Ca, Mg, Na, and Mn. These findings comply well with the concept of sustainable agriculture focused on utilizing environmentally friendly compounds derived from sources of natural origin while exhibiting enhanced efficacy.