Gibberellin-Like Activity of Helminthosporic Acid Analogues

Abstract

The activity of some analogues of helminthosporins was tested in three gibberellin bioassay systems. Three compounds showed considerable activity in the barley endosperm bioassay, five were slightly active and three were inactive. The response curves were frequently steeper than that of gibberellic acid, and sometimes bimodal. Comparisons of the structures of active and inactive compounds indicate that the hydroxymethyl moiety of natural helminthosporins is not necessary for biological activity. The carboxyl group is required for activity and appears to have favoured spatial requirements. Similar structureactivity relationships were suggested for the Tan-ginbozu rice bioassay but those for the Rumex leaf senescence bioassay were different.