Effects of auxin on polyphenol accumulation and the development of phenylalanine ammonia-lyase activity in darkgrown suspension cultures of Paul's Scarlet rose.
1. Under a variety of cultural conditions, including variation in initial auxin and carbohydrate levels, there appears to be a close correlation between phenylalanine ammonia-lyase (PAL) activity and polyphenol synthesis, although there is some discrepancy in timing between the maximum rate of polyphenol accumulation and the period of maximum enzyme content. The diverse responses of the two parameters to cycloheximide and actinomycin-D inhibition suggest that at certain phases of development, PAL is not a rate-limiting step in polyphenol synthesis. 2. Based on the sensitivity to antibiotic inhibitors, it is concluded that PAL is synthesised de novo, that it is subject to rapid turnover at all stages of development and that continuous RNA synthesis is required to sustain the increase in PAL levels. 3. When added to lag- and early exponential-phase cells high 2,4-D concentrations retard the development of PAL activity with a concomitant delay in polyphenol accumulation. Once the increase in PAL activity has started, the early stage of development of the enzyme is less sensitive to high hormone levels than is polyphenol synthesis. It is suggested, therefore, that in addition to inhibiting the initiation of PAL synthesis, high auxin levels may also inhibit some other component(s) of the biosynthetic pathway. High 2,4-D levels (10(-3)M) do not inhibit the activity of PAL in vitro.
The Department of Botany, University of Birmingham, England.
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Davies