No abstract

Cultured Cupressus lusitanica cells induced by various stresses are thought to produce different complexes of defense chemicals to optimize defense. To compare the induced products of two stimulations, we investigated the emission of monoterpenes, biosynthesis of b-thujaplicin, and accumulation of lignin in mechanically stressed and fungal elicited cultured C. lusitanica cells. Both mechanical stress and fungal elicitor caused emission of qualitatively similar monoterpene blends indicating de novo biosynthesis of these compounds after stimulation, while mechanical stress alone is sufficient to induce fungal elicitor-related monoterpene emission. Sabinene and limonene were the dominant compounds over the time course in both volatile blends. Although the emitted volatile blends were qualitatively similar, the time course and the relative ratios of the constituents of the volatile blends differed with the type of stimulation. While fungal elicited cells produced significant amounts of b-thujaplicin over the 5-day time course, no b-thujaplicin was observed in the mechanically stressed cells. The production of b-thujaplicin was the main dissimilarity of the induced products of these two treatments, suggesting that synthesis of b-thujaplicin is not a general response to all types of stresses, but is a specific response and serves as a strong toxic compound against already invaded fungus. Significantly higher amounts of lignin accumulations were observed in the fungal elicited and mechanically stressed cells on the 5th day after induction. Based on these results, we suggest the composition of induced products was dependent on the method of stimulation.

A cell culture of Cupressus lusitanica was used to investigate the reaction of a plant to certain airborne chemicals. Compared with laboratory and field methods using intact plants or tissues, a cell culture is advantageous because it is not affected by environmental factors, and the experiments are easier to reproduce. When exposed to an elicitor, our cell line produces 10 monoterpenes and β-thujaplicin, which is a strong phytoalexin. These monoterpenes are emitted into the vapor phase and are expected to play a role in airborne signaling. In the present study, the cells were exposed to monoterpene vapors, and the volatiles present in the culture flasks were monitored. When the culture cells were exposed to low doses of sabinene, we detected γ-terpinene and p-cymene. After exposure to γ-terpinene, we found p-cymene and terpinolene, whereas p-cymene exposure resulted in terpinolene emission. By contrast, the other seven monoterpenes we investigated did not induce any emissions of other monoterpenes. These results strongly suggest that in C. lusitanica a signaling cascade exists that starts with the emission of sabinene and moves to γ-terpinene, p-cymene, and finally to terpinolene, which accelerates the production of the phytoalexin β-thujaplicin.