Abstract
Endogenous melatonin (MEL) and abscisic acid (ABA) are involved in the adaptation of plants to environmental stresses. The application of exogenous serotonin (SER) to plants can enhance their tolerance to abiotic stress, such as cold. However, the mechanism associated with serotonin-mediated defense against cold-induced damage in mangroves is still poorly understood. In this study, we demonstrated that mangrove (Kandelia obovata) seedlings sprayed with 200 μmol·L-1 serotonin exhibited enhanced cold tolerance, as shown by reduced damage to leaves and loss of photosynthesis when exposed to low-temperature conditions. The mechanism associated with the cold adaptation of K. obovata seedlings upon treatment with serotonin was subsequently investigated by transcriptomic analysis. Serotonin treatment caused changes in differentially expressed genes (DEGs) involved in the regulation of melatonin (MEL) and ABA biosynthesis and defense responses against cold stress. Under low-temperature stress, serotonin-treated seedlings showed a significant increase in the endogenous levels of melatonin and ABA. By contrast, under normal growth conditions, K. obovata seedlings treated with serotonin displayed no substantial change in melatonin level, whereas ABA level significantly increased. These findings demonstrated that serotonin treatment might play an important role in the enhanced resistance to cold in K. obovata and that such an effect would depend on the activation of endogenous melatonin and ABA synthesis.