Ethylene is the key signal in the accumulation process of scopoletin in noni (Morinda citrifolia)

Abstract Noni (Morinda citrifolia) has been widely used both as medicine and food in tropical areas. In recent years, its medicinal value has been the subject of increasing attention around the world. Scopoletin, belonging to the family of coumarins, is a useful parameter for evaluating the results of a harvest season and the quality of noni. It can also serve an important function as a metric in the quality assurance of unprocessed noni fruit juice and commercial noni products. Therefore, in this work, we sought to clarify the relationship between differences in scopoletin content and a cell suspension culture system of noni, and verified these findings using noni fruit. First, a cell suspension of noni was treated with ethephon (ETH), methyl jasmonate (MJ), abscisic acid (ABA), gibberellin 3 (GA3) or salicylic acid (SA) for one successive generation cycle (8 days). We found that treatment with 0.075 mg/L ETH and 1.5 mg/L MJ led to the greatest induction of coumarins. Subsequently, we determined the concentration of scopoletin in a noni cell suspension after induction with a panel of hormones. We found that ETH was the most beneficial molecule to the synthesis of scopoletin. Next, we verified these findings with application to the ripening process of noni fruit. Specifically, we found that the scopoletin content in summer noni fruit reached its maximum on the 6th day and in winter fruit on the 10th day after harvest. In addition, spraying exogenous ETH on winter fruit accelerated the maximum content of scopoletin to appear on the 4th day. In conclusion, to select for noni fruit with high scopoletin content, fruit should be used 6–10 days after harvest. Further, our data suggest that the most efficient method to obtain high scopoletin content is using an ethylene-induced cell suspension system.