The elicitation of phytoalexins by Ca 2+ and cyclic AMP in carrot cells

Abstract

Addition of calcium ionophore A23187 or dibutyryl cyclic AMP (dBcAMP) to carrot ( Daucus carota L.) cell culture induced the production of 6-methoxymellein, a phytoalexin of carrot, in a dose-dependent manner. Several reagents known to suppress the cytoplasmic calcium concentration appreciably inhibited elicitor-promoted phytoalexin production in carrot cells. The addition of elicitor to the carrot culture caused a rapid increase in the intracellular level of cyclic AMP. Treatments of the cells with theophylline or cholera toxin stimulated the biosynthesis of 6-methoxymellein even in the absence of elicitor. These observations suggested that Ca 2+ and cyclic AMP participate as second messengers in the regulation of 6-methoxymellein production in cultured carrot cells. Addition of verapamil to carrot cell culture markedly inhibited 6-methoxymellein production when it was added within 30 min after elicitor-treatment of the cells, but no inhibitory effect was observed after 60 min. The results suggest that these messengers function in an early stage of the elicitation process. Carrot cells which were previously treated with verapamil accumulated only small amounts of 6-methoxymellein following the addition of dBcAMP. In contrast, cells incubated initially with dBcAMP accumulated the phytoalexin at levels comparable to the control when verapamil was added to the culture.