Kaurene oxidase inhibitors

Figure 2. Growth retardants Kaurene oxidase inhibitors.

The triazoles and related growth retardants are not general inhibitors of plant cytochrome P-450 monooxygenases [39]. Their action appears to be confined to methyl hydroxylases, with which they interact to differing extents depending on structure. Apart from e f-kaurene oxidase, there are several other such enzymes that are involved in important metabolic pathways (Fig. 5), the products of which may influence growth. These are potential sites of action and will be considered below. 

Paclobutrazol is a triazole plant growth retardant which also has fungicidal properties [1]. It is an inhibitor of cytochrome P-450 dependant enzymes such as ent-kaurene oxidase and sterol 14a-methyl-demethylase [1]. The fungicidal activity of azole compounds is believed to result from the inhibition of sterol 14a-demethylation. This causes an accumulation of 14a-methylsterols and loss of ergosterol which may have adverse effects on membrane properties [2]. However, there is evidence for other essential requirements for sterol In cell proliferation in addition to a membrane structural role [3-6].For example, in yeast mutants traces of ergosterol stimulate phospholipid formation [7] and protein kinase activity [8]. This report describes the effects of paclobutrazol on the sterol and phospholipid compositions of membranes from plant and yeast cultures. 

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