Jasmonic acid (JA) and its methyl ester play a crucial role in the signal transduction pathway that leads to the induction of secondary metabolites in plant cell cultures. When plant cell suspensions of Rauvolfia canescens and Eschscholtzia californica are exposed to a yeast elicitor, JA and its methyl ester accumulate rapidly and transiently. Exogenous application of methyl jasmonate also induces the synthesis of low molecular weight compounds and activates genes involved in the chemical defense mechanisms of plants, such as phenylalanine ammonia lyase (PAL), which is essential for the biosynthesis of secondary metabolites. The study shows that JA and its derivatives are integral to the intracellular signal cascade that begins with the interaction of an elicitor molecule with the plant cell surface and results in the accumulation of secondary compounds. This process is not limited to specific plant species but is observed in various plant cell cultures, including those of 36 different species. The induction of secondary metabolism by JA is not restricted to a particular type of compound but is general to a wide range of low molecular weight substances, including flavonoids, guaianolides, anthraquinones, and various alkaloids. The study also demonstrates that JA induces the expression of genes involved in secondary metabolism, as evidenced by the increased levels of PAL poly(A)+ RNA and enzyme activity in soybean cell cultures. The results support the hypothesis that JA and its derivatives are key signal molecules in the elicitation process leading to the biosynthesis of secondary metabolites in plant cell cultures. The findings suggest that JA is involved in the regulation of plant defense responses, including the synthesis of phytoalexins and the induction of proteinase inhibitors. The study also highlights the importance of JA in plant defense mechanisms, as it is involved in the regulation of plant senescence, wound response, and mechanical stimulation. The results indicate that JA is a natural hormonal regulator that plays a central role in the induction of defense responses in plants.Jasmonic acid (JA) and its methyl ester play a crucial role in the signal transduction pathway that leads to the induction of secondary metabolites in plant cell cultures. When plant cell suspensions of Rauvolfia canescens and Eschscholtzia californica are exposed to a yeast elicitor, JA and its methyl ester accumulate rapidly and transiently. Exogenous application of methyl jasmonate also induces the synthesis of low molecular weight compounds and activates genes involved in the chemical defense mechanisms of plants, such as phenylalanine ammonia lyase (PAL), which is essential for the biosynthesis of secondary metabolites. The study shows that JA and its derivatives are integral to the intracellular signal cascade that begins with the interaction of an elicitor molecule with the plant cell surface and results in the accumulation of secondary compounds. This process is not limited to specific plant species but is observed in various plant cell cultures, including those of 36 different species. The induction of secondary metabolism by JA is not restricted to a particular type of compound but is general to a wide range of low molecular weight substances, including flavonoids, guaianolides, anthraquinones, and various alkaloids. The study also demonstrates that JA induces the expression of genes involved in secondary metabolism, as evidenced by the increased levels of PAL poly(A)+ RNA and enzyme activity in soybean cell cultures. The results support the hypothesis that JA and its derivatives are key signal molecules in the elicitation process leading to the biosynthesis of secondary metabolites in plant cell cultures. The findings suggest that JA is involved in the regulation of plant defense responses, including the synthesis of phytoalexins and the induction of proteinase inhibitors. The study also highlights the importance of JA in plant defense mechanisms, as it is involved in the regulation of plant senescence, wound response, and mechanical stimulation. The results indicate that JA is a natural hormonal regulator that plays a central role in the induction of defense responses in plants.