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.

Use of ammonium salts or binary mixtures derived from amino acids, glycine betaine, choline and indole-3-butyric acid as plant regulators

“…The developed synthesis method yielded ve reaction products 1-5: 1, 2 and 3 were white solids, and 4 was obtained as a wax. The synthesized ionic liquid (5) was obtained following a methodology described in the literature 26 and used together with IBA as reference substances ( Table 1).…”

“…By contrast, ionic liquid 5 and the potassium salt of IBA were highly soluble in water. 26,39 Thus, leaching of these products into deep layers of soil would be mitigated were these substances released into the environment.…”

“…The quantity of plant growth hormones used was correlated with the stage of plant growth and the time over which the plant interacted with the solution. 26 A commercial preparation containing IBA (Rhizopon AA -REF) was used in the control test. The results ( Fig.…”

“…25 To the best of our knowledge, the only study on using IBA (in the form of ammonium salts) as a plant growth regulator was published in 2020. 26 The main aim of this study was to develop a synthesis method for an amino acid (L-arginine, L-histidine, L-proline), glycine betaine or choline and indole-3-butyric acid. It was determined whether the selected substrates occurred as protic ammonium salts or binary mixtures.…”

Conversion of l‐Tryptophan Derivatives into Biologically Active Amino Acid Ionic Liquids

“…This dependence may be related to the hydrophobicity of the salt, which decreases with the extension of the alkyl chain in the ammonium cation, as described in our previous studies. [41,42] The introduction of the tetraalkylammonium cation into the structure of l-tryptophan caused a rapid increase in its solubility at 25°C in water, methanol, acetone and 2-propanol. According to the literature, only small amounts of l-tryptophan are soluble in water (11 g per 1 L water), hot alcohol, dilute acid and hydroxide solutions.…”