Growth hormone biosynthesis inhibitors

Finally, chemical substances are now available to the vine-grower to slow vine vigor and accelerate the maturation process. These are usually growth hormone biosynthesis inhibitors (Reynolds, 1988). 

Plant hormone biosynthesis and metabolism are influenced and modified, too, as already mentioned, by a large number of typical secondary plant constituents of quite different structures (Eef. 5, 6). For instance, it has been shown that some oi-disubstituted acetic acid derivatives are active both as antiauxins and as inhibitors of the biosynthesis of cyclic terpenoids. Thus, some more simple model compounds synthesized by ourselves, for example substituted a-phenoxy-isobutyrio acids, are not only competitive auxin inhibitors but they are also able to inhibit both the gibberellin and sterol biosynthesis. The same is true for some well known plant growth retardants, such as CCO or AMO 1618, which are inhibitors of gibberellin biosynthesis both in plants and in Fus ium moniliforme, but at the same time they are inhibiting and modifying also the biosynthesis of steroids in the respective organisms as well as in animal in vitro systems (Eef. 29) ... 

The effects of treatment with selegiline, an MAO-B inhibitor, on plasma levels of insulin-like growth factor I (IGF-I) (as indicator of GH secretion), levels of monoamines and their metabolites, and the activity and content of tyrosine hydroxylase — the rate-limiting enzyme in the biosynthesis of catecholamines — in the hypothalamus and hypophysis of old animals have been studied. It is believed that the antiaging effects of selegiline are due to restoration of hypothalamic hormones. 

In an indirect manner, the lipoxygenase reaction in higher plants appears to be implicated in the biosynthesis of abscisic acid, a further senescence hormone [23-25], Abscisic acid is formed from the carotenoid violaxanthin that is converted into xanthoxin, which is a plant growth inhibitor and at the same time a precursor of abscisic acid. The formation of xanthoxin requires the co-oxidative activity of a lipoxygenase-linoleic (or a-linolenic) acid system. 

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