A NEW PHOTOSYSTEM-II ELECTRON-TRANSFER INHIBITOR FROM SORGHUM-BICOLOR

Our study of the mechanism(s) by which sorgoleone (1) acts as a photos ystem II (PS II) inhibitor led to the isolation of a new benzoquinone derivative, (Z,Z)-8',11',14'-pentadecatriene]-rho-benzoquinone (2), fr om the root exudate of sorghum. The structure of 2, which is being giv en the name 5-ethoxy-sorgoleone, was determined by spectroscopic means . A methoxy derivative (3) of 1 was also prepared. Both 2 and 3 caused a reduction in oxygen evolution by thylakoid membranes and induced va riable chlorophyll fluorescence. These compounds, however, were less a ctive inhibitors of PS II than 1.