The Development of Plant Hormone Research in the Last 60 Years

Abstract

The development of ideas traced by Dr. Heslop-Harrison turned out to be the forerunner of a real revolution in our concepts of how the higher plant is integrated and organized. It will not be possible to enter on such a detailed enquiry as the previous speaker, because the field has become so much broader. The concept of a growth hormone arose directly out of the work of Arpad Paal and, like the work of Darwin and Boysen-Jensen before him, was founded firmly on the nature of tropisms. (The 1909 work of Fitting on the post-floration phenomena in orchids, caused by a postulated “pollenhormon,” was quite separate and is an exception to the clear line that can be traced through tropisms, especially phototropism.) Unlike the early developments in animal hormone studies, the plant hormone concept depended from the first on the idea of a quantitative response, i.e., some proportional relationship between the quantity of hormone and the intensity of the response. By contrast, gastric secretion, thyroid action, male and female sexual development (e.g., comb formation in cockerels) were observed rather as all-or-none phenomena, at least at first; later, of course, bio-assays were developed whose quantitative nature allowed the beginnings of chemical isolation.