Investigation of the Effects of MT on the Antioxidant Capacity of Impatiens walleriana Under Water Deficit In Vitro

Impatiens walleriana is an ornamental plant highly susceptible to water deficit. Given the multifunctional role of melatonin (MT) in plant protection, this study evaluated the efficacy of MT treatment on plant during water deficit in alleviating stress. Shoots were micropropagated in vitro on media supplemented with MT (0, 10, 50, 100 and 150 µM), alone or combined with 3% polyethylene glycol (PEG). Morphological, physiological, and biochemical parameters were analysed after treatment. Treatment of shoots with 10 µM MT under optimal conditions resulted in a slower root growth and development, increased DPPH content and maximum superoxide dismutase activity. Shoots treated with a higher concentration of MT showed reduced values for all morphological parameters, while 150 µM MT had an inhibitory effect on scarification and induced the highest values for H2O2, total phenolic, and DPPH contents, as well as catalase and peroxidase activity. Water deficit alone significantly reduced shoot height, shoot and root fresh weight, photosynthetic pigment content, and DPPH activity, while it increased osmoprotectants, H2O2, and peroxidase activity. Plants treated with 50 μM MT during water deficit almost did not develop roots, and the application of higher concentrations of MT (100 and 150 μM) reduced shoot development with increased proline content, reduced POX activity, and inhibited root formation. This is the first study to investigate the effects of MT on the antioxidant capacity of I. walleriana under water deficit and provides guidance for future research on stress-tolerance mechanisms.