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1. In dark-grown cell suspension cultures of Paul's Scarlet rose (Rosa sp.), polyphenol accumulation is essentially restricted to late- and post-exponential phase cells. The range of polyphenols synthesised is extensive, involving at least fourteen different compounds which show a characteristic pattern of development over the growth cycle. 2. The duration of polyphenol accumulation is largely determined by the availability of carbohydrate, while the initiation and initial rate of synthesis is largely influenced by a complex of factors of which auxin concentration and light are most important. High 2,4-D concentrations (5x10(-5)M) supress accumulation by delaying initiation and reducing the subsequent rate of synthesis. High intensity illumination (6000 Lux) partially reverses the inhibition of polyphenol synthesis at 5x10(-5)M 2,4-D, and enhances accumulation at lower auxin concentrations (5x10(-7)M 2,4-D). 3. Illuminated cultures also accumulate anthocyanin. Initiation of pigment synthesis is insensitive to the auxin concentration of the medium, and higher hormonal levels (5x10(-5)M 2,4-D) increase net anthocyanin accumulation by prolonging the period over which it is synthesised.

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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.

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