Melatonin Improves Waterlogging Tolerance of Malus baccata (Linn.) Borkh. Seedlings by Maintaining Aerobic Respiration, Photosynthesis and ROS Migration

Abstract

Waterlogging, one of the notorious abiotic stressors, retards the growth of apple plants and reduces their production. Thus, it is an urgent agenda for scientists to identify the suitable remedies for this problem. In the current study, we found that melatonin significantly improved the tolerance of apple seedlings against waterlogging stress. This was indicated by the reduced chlorosis and wilting of the seedlings after melatonin applications either by leaf spray or root irrigation. The mechanisms involve in that melatonin functions to maintain aerobic respiration, preserves photosynthesis and reduces oxidative damage of the plants which are under waterlogging stress. Melatonin application also enhances the gene expression of its synthetic enzymes (MbT5H1, MbAANAT3, MbASMT9) and increases melatonin production. This is the first report of a positive feedback that exogenous melatonin application promotes the melatonin synthesis in plants. A post-transcriptional regulation apparently participated in this regulation. When exogenous melatonin meets the requirement of the plants it is found that the protein synthesis of MbASMT9 was suppressed. Taken together, the results showed that melatonin was an effective molecule to protect plant, particularly apple plant, against waterlogging stress.

Apple tree flowering is mediated by low level of melatonin under the regulation of seasonal light signal

“…This reaction may occur in chloroplast due to the fact that majority of melatonin is synthesized in chloroplasts. 35 When relatively low exogenous melatonin was applied, the post-transcriptional regulation of the melatonin synthetic genes was impacted as reported by Zheng et al 55 However, when relatively high concentration of melatonin was applied the dramatic changes of MdASMT9 expression was observed at the levels both in transcription and translation ( Figure 6A,C). These changes lead to the M shape pattern of melatonin production observed in the study.…”

Role of Melatonin and Plant‐Growth‐Promoting Rhizobacteria in the Growth and Development of Plants

“…Plants generate large amounts of reactive oxygen species (ROS) during photosynthesis especially under stressful environment like drought, salinity, and cold . Excessive ROS accumulation leads to oxidative stress that causes damage to DNA, RNA, and enzymes.…”

“…Unlike classical antioxidants, melatonin due to its amphiphilic nature can easily pass through cellular membranes. Metabolites of melatonin also act as antioxidants by scavenging free radicals thus forming antioxidant cascade reaction . When plants are treated with exogenous melatonin, several anti‐stress related genes are up‐regulated that induce endogenous melatonin production under stress conditions .…”

“…Waterlogging is also an important environmental issue that causes huge economic losses and it was found that exogenous melatonin enhances tolerance of apple plants against water logging stress. In water logged conditions, melatonin helps the plant to maintain aerobic conditions, chlorophyll content, and photosynthetic rate …”

“…Melatonin is an important hormone produced by the pineal gland of animals having pleiotropic activities and has been identified in plants for the first time in 1995 . Due to its amphiphilic nature, it is distributed in different cell compartments including mitochondria, cytosol, and chloroplast . The research on melatonin is increasing because of its diversified role in plants as it is involved in seed germination, biomass production, increased photosynthesis, senescence delay, delayed flowering, circadian rhythm, fruit ripening, and biotic and abiotic stress responses (Figure ).…”