Signal interaction between nitric oxide and hydrogen peroxide in heat shock-induced hypericin production of Hypericum perforatum suspension cells

Heat shock (HS, 40 degrees C, 10 min) induces hypericin production, nitric oxide (NO) generation, and hydrogen peroxide (H(2)O(2)) accumulation of Hypericum perforatum suspension cells. Catalase (CAT) and NO specific scavenger 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) suppress not only the HS-induced H(2)O(2) generation and NO burst, but also the HS-triggered hypericin production. Hypericin contents of the cells treated with both NO and H(2)O(2) are significantly higher than those of the cells treated with NO alone, although H(2)O(2) per se has no effects on hypericin production of the cells, which suggests the synergistic action between H(2)O(2) and NO on hypericin production. NO treatment enhances H(2)O(2) levels of H. perforatum cells, while external application of H(2)O(2) induces NO generation of cells. Thus, the results reveal a mutually amplifying action between H(2)O(2) and NO in H. perforatum cells. CAT treatment inhibits both HS-induced H(2)O(2) accumulation and NO generation, while cPTIO can also suppress H(2)O(2) levels of the heat shocked cells. The results imply that H(2)O(2) and NO may enhance each other's levels by their mutually amplifying action in the heat shocked cells. Membrane NAD(P)H oxidase inhibitor diphenylene iodonium (DPI) and nitric oxide synthase (NOS) inhibitor S,S'-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea (PBITU) not only inhibit the mutually amplifying action between H(2)O(2) and NO but also abolish the synergistic effects of H(2)O(2) and NO on hypericin production, showing that the synergism of H(2)O(2) and NO on secondary metabolite biosynthesis might be dependent on their mutual amplification. Taken together, data of the present work demonstrate that both H(2)O(2) and NO are essential for HS-induced hypericin production of H. perforatum suspension cells. Furthermore, the results reveal a special interaction between the two signal molecules in mediating HS-triggered secondary metabolite biosynthesis of the cells.