Correlation of tyrosinase activity and betacyanin biosynthesis induced by dark in C3 halophyte Suaeda salsa seedlings

The role of tyrosinase (EC 1.14.18.1 and EC 1.10.3.1) in the secondary metabolism of plants still remains unclear, and the involvement of both hydroxylation and oxidation activities of tyrosinase in betalain biosynthesis has been proposed, but has not yet been shown conclusively. Betalains are an important class of water-soluble pigments, which comprise the red–violet betacyanins and the yellow betaxanthins, and accumulate in most families of the Caryophyllales and some higher fungi. In this article, the role of tyrosinase in dark-induced betacyanin biosynthesis in Suaeda salsa was examined. Seeds of the halophyte Suaeda salsa were cultured in the dark for 3 days and betacyanin accumulation was induced significantly in cotyledons of Suaeda salsa seedlings. Accumulated betacyanin in cotyledons of the dark-grown seedlings decomposed with time in light. As the betacyanin content declined, the hydroxylation and oxidation activities of tyrosinase extracted from cotyledons of the dark-grown seedlings decreased with time in light. The apparent molecular mass of tyrosinase in cotyledons of Suaeda salsa seedlings was about 60 kDa estimated by SDS-PAGE, enzyme activity staining and Western blotting. Furthermore, the tyrosinase only synthesized in the cotyledons of dark-grown Suaeda salsa seedlings, and declined with time in light, which was paralleled by the decreases of tyrosinase activity and betacyanin content in light. These results suggest that the specific tyrosinase is positively correlated with betalain biosynthesis, and betacyanin biosynthesis is induced by dark via synthesis of tyrosinase in Suaeda salsa.