Kenneth Vivian Thimann

1982 Balzan Prize for Pure and Applied Botany

For his elucidation of the functions of hormones in the control and development of plants, in particular for having isolated the growth hormone (auxin) and clarified its chemical structure. This discovery has also been of great practical value in agriculture.

Kenneth Vivian Thimann (1904 – 1997), born in Ashford, U.K., in 1904, Emeritus Professor at the University of California (Santa Cruz), currently working at the laboratories named after him (Thimann Laboratories), is the author of about three hundred publications in the field of plant physiology. The results achieved, particularity the elucidation of the functions of hormones in the control and development of plants, are highly considered by the scientific community.
In 1933 Thimann concluded the biochemical research on the substance of which Fritz Went discovered the stimulating action on plant growth, demonstrating that this substance was 3-indol-acetic acid, known today as auxin.
Thimann and his coworkers showed that synthetic auxin had an inhibiting effect on bud formation, which was however antagonized by the promotory effect of another hormone, kinetin. In this field of study Thimann’s work developped with the analysis of the functional rôle of plant hormones and their interactions in plant growth and development. He has demonstrated that the hormones are active, in different ways, at three concentration levels and established the optimum curves which are different for leaves, buds and stems. The elucidation of the way in which individual hormones act in connection with other hormones present is considered as one of his greatest achievements.
The broad spectrum of Thimann’s interests extends to many other fundamental problems in the field of plant physiology where his research has always been of the same high quality. Thus he has analyzed the biosynthesis of anthocyanins (pigments responsible for the colour of flowers and fruit), the action of the various zones of the light spectrum on photosynthesis, the factors controlling the mechanism of ageing of leaves, etc.
The impact of his discoveries on agriculture and horticulture cannot be underestimated. Synthetic substances imitating the effect of auxins are now used to promote growth of shoots. Apple trees are repeatedly sprayed with auxin at the appropriate time to prevent premature failing of fruit. Auxin is also used as herbicide, since it is toxic in high concentrations.
In addition to specific papers, Thimann has also published many widely used treatises. He is also an inspiring leader of more than a generation of botanists and is regarded as the doyen of a line of research that has revolutionized plant physiology.

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