Abstract
Attention is drawn to the need for detailed studies in mammalian systems, in vitro and in vivo, of the ‘natural' substances which play a role in the regulation of plant growth, known as ‘plant hormones'. Among the latter, certain gibberellins, which are growth promoters (GA3), appear to have oestrogenic and carcinogenic action in experimental rodents. Abscisic acid (ABA), which acts as an antagonist of GA3, and induces ‘dwarfing', senescence, leaf and fruit drop in plants, has as yet not been tested for anti-oestwgenic, or anti-carcinogenic action in mammals, though it was synthesized 30 years ago. The recent finding that fruits and vegetables appear to prevent and/or inhibit neoplasias in humans, as do certain isolated constituents of plants (though at relatively high concentrations), indicates the urgent need to evaluate the potential of ABA as a therapeutic agent. Moreover, as ABA has very high ‘hormonal' activity in plants, its adventitious presence in preparations and substances isolated from plants has to be considered.