Role and regulation of cAMP in seed germination of Phacelia tanacetifolia

Although adenosine 3′,5′-cyclic monophosphate (cAMP) is known as a key second messenger in many living organisms, regulating a wide range of cellular responses, its biological function in higher plants is not well understood. In this study, the role and the regulation mechanism of cAMP in seed germination of Phacelia tanacetifolia Benth. were examined. The cAMP level of the seeds incubated under optimal conditions for germination showed a transient elevation before germination. When the seeds were exposed to light or supraoptimal temperature during incubation, elevation of cAMP levels as well as germination of the seeds were inhibited. Addition of membrane-permeable cAMP to the medium restored the germination rates of these seeds, suggesting that cAMP functions during germination. Treatment of the seeds with gibberellin (GA) was also effective to restore the elevation of cAMP levels and germination of the seeds. Uniconazole, a potent inhibitor of GA biosynthesis, blocked elevation of cAMP level under optimal conditions for germination. These results suggest that cAMP plays a role in the regulation of germination and that the cAMP level is regulated by GA in P. tanacetifolia seeds.