Root-Zone Cooling Effects on Growth, Physiological, and Biochemical Responses of Taraxacum coreanum Under Hydroponics

Low root-zone temperatures (RZTs) are known to cause various physiological changes in plants, which ultimately result in reduced overall plant growth and productivity. However, the effects of temperature on the below-ground parts remain largely unknown; a notable gap exists in understanding the effects of low RZTs on plants. Therefore, we explored the impact of short-term root-zone temperature cooling (RZTC) on the growth, physiological responses, and amino acid levels of Taraxacum coreanum in hydroponic systems. We also investigated the monoamine oxidase (MAO) inhibitory activity of T. coreanum leaves and roots following RZTC treatment. T. coreanum roots were exposed to low-temperature nutrient solutions over 5 days to cool the root zone at 53 days after sowing. RZTC treatments included gradual cooling (GC), with temperatures gradually decreasing from 15 to 5 °C for 5 days, and rapid cooling (RC), in which roots were exposed to 5 °C for 5 days. RZTC caused a decrease in total amino acid content, except for glutamic acid and proline in T. coreanum leaves. In roots, the RC treatment significantly increased proline and glutamine, with glutamine exhibiting the most significant changes, thus increasing total amino acids. MAO inhibition assays indicated improved activity in both leaves and roots following RZTC treatments, with RC enhancing the inhibitory effects to a greater extent than GC treatment. Therefore, exposing the roots of T. coreanum to 5 °C for 5 days can result in roots with high glutamine content and leaves and roots with improved inhibition rates against MAO.