The flowering stimulus and possible involvement of prostaglandins in the flowering of Pharbitis nil : review article

The putative flowering stimulus ('florigen') is discussed in relation to the possible involvement of prostaglandins in the flowering of the short-day plant Pharbitis nil. The postulated existence of 'florigen' is based on grafting experiments in the main, but it has been confounded by the failure to isolate a chemical which results in long-day or short-day plants that flower under non-inductive conditions. Prostaglandins play a possible role in the flowering of P. nil. A hypothetical model is presented of the interaction of a gibberellin with prostaglandin F2a in the plasma membrane of the leaf, and the subsequent activation of cyclic-AMP in the cytosol, with the further result that a cascade of reactions is initiated. The product(s) of the cascade could be the transmissible stimulus from the leaf to the apex of the plant. This trigger could be extended on short days; during long days, a low molecular weight phenolic acid (such as salicylic acid) could be an inhibitor of prostaglandin biosynthesis in the leaf and thus of flowering.