Effects of G protein and cGMP on phytochrome-mediated amaranthin synthesis in Amaranthus caudatus seedlings

The effects of G protein and cGMP on phytochrome-mediated amaranthin biosynthesis inAmaranthus caudatus seedlings were studied. It was shown that G protein agonist cholera toxin induced amarathin synthesis in darkness, whereas G protein antagonist pertussis toxin inhibited red light-induced amaranthin synthesis. Amaranthin synthesis was also induced by exogenous cGMP, while the amaranthin biosynthesis induced by cholera toxin, red light and exogenous cGMP was inhibited by genistein. L Y-83583, an inhibitor of guanylyl cyclase, inhibited the amarenthin synthesis induced both by red light and cholera toxin, while it was not able to inhibit the amaranthin synthesis induced by exogenous cGMP. These results suggest that G protein, guanylyl cyclase and cGMP were the candidates in phytochrone signal transduction chain for red light-induced amaranthin biosynthesis and the red light signal transduction chain might be as follows: red light → phytochrome → G protein → guanylyl cyclase → cGMP.