Identification of Endogenous Substances Involved in Sclareol-Induced Chlorophyll Reductions in Arabidopsis.

Sclareol, a natural diterpene, exhibits diverse physiological activities in plants, microorganisms, and animals. Exogenous application of sclareol to Arabidopsis thaliana leaves induces chlorosis-like symptoms accompanied by a reduction in chlorophyll content. In our previous study, a bioassay-guided fractionation approach was employed to isolate endogenous compounds responsible for this decrease, leading to the identification of campesterol and stigmasterol as active phytosterols. Notably, this approach also indicated the presence of additional active substances in fractions lacking these phytosterols. In the present study, we identified α-pinene, oleic acid, triolein, and pipecolic acid as additional compounds capable of reducing chlorophyll content. Exogenous application of each compound to Arabidopsis leaves resulted in a dose-dependent decline in chlorophyll levels. Furthermore, sclareol treatment increased the endogenous accumulation of these metabolites, along with the expression of genes involved in their biosynthesis. Because phytosterols, terpenoids, lipids, and pipecolic acid have been implicated in plant growth and development, stress responses, and disease resistance, the metabolites identified in this study are likely to contribute not only to sclareol-induced chlorophyll reduction but also to other physiological responses elicited by sclareol. Collectively, these findings suggest that sclareol triggers coordinated metabolic reprogramming in Arabidopsis, leading to the accumulation of multiple bioactive metabolites that mediate diverse physiological processes.