Effects of Melatonin and AVG on Plant Growth of Three Pilea Species in Darkness

Ornamental foliage plants are valued for their catchy leaves with diverse shapes and colors, but dark-induced plant senescence or deterioration during transport greatly limits the quality of foliage plants. Melatonin is an important signaling molecule that affects pleiotropic developmental progress in plants. Aminoethoxyvinylglycine (AVG) is a potent inhibitor of ethylene biosynthesis and is extensively used to delay plant senescence and fruit ripening. In this study, we compared the effects of melatonin and AVG on alleviating plant deterioration of three Pilea species (P. cadierei (PC), P. involucrata (PI), and P. mollis (PM)) through foliar sprays of different concentrations of melatonin or AVG prior to darkness treatment. Our results showed that PC, PI, and PM exhibited distinct responses to melatonin or AVG. PM was the most sensitive species and it exhibited significant increases in stem height, leaf area, chlorophyll, and anthocyanin content in response to 50, 100, and 150 μmol·L−1 of melatonin; similar responses to 150 and 200 μmol·L−1 of melatonin were observed in PI with regard to these plant characteristics. By contrast, much weaker effects of AVG on these plant characteristics were observed in PM and PI, although it increased their Fv/Fm values as did melatonin. Unlike PM and PI, PC is generally not responsive to all melatonin and AVG treatments, although AVG treatments did change its stem elongation. These results may provide growers with science-based information for future practical application of melatonin to improve the post-harvest quality of ornamental plants.