Sucrose (0.04 to 0.12 M) induces accumulation of both total phenolics and anthocyanin in leaf discs of grapevine (Vitis vinifera L.) incubated in intermittent light. Abscisic acid (20 FM) and 2-chloroethyl phosphonic acid (60 FiM) act synergistically with the sucrose to enhance its induction of both total phenolics and anthocyanin. The magnitude of this interaction depends on leaf age. Nitrate (30 mm) inhibits sucrose induction of phenolics and anthocyanin. Levels of total phenolics and anthocyanin changed independently.The identity of the inducers of phenolic biosynthesis in plants is of considerable interest due to the wide range of environmental stimuli which lead to accumulation of phenolic substances in plant tissues (27). Phytochrome-mediated light effects on activity of PAL3 are well documented (2, 17, 27), but little is known of nonphytochrome inducers of phenolic biosynthesis. Among externally applied substances shown to possess regulatory properties over anthocyanin accumulation, or over activity of enzymes of the phenolic biosynthetic pathway, are sugars (22, 26), nitrate (14, 21), ethylene (3, 6), ABA (25), and kinetin (12,23). We are studying the effect of these substances on both total phenolic and anthocyanin accumulation to elucidate mechanisms of regulation of phenolic biosynthesis. The fact that ABA and reducing sugar levels are known to change in skins of grape berries (4, 5) at a time of accumulation of phenolic compounds in that tissue has led us to test their effect, in particular, on anthocyanin and phenolic accumulation in leaf and fruit tissue of grapevine.In this paper we report on treatments which stimulate and inhibit accumulation of both total phenolics and anthocyanin, and on a system where regulation of these two phenolic pools can be studied separately. MATERIALS AND METHODSExperiments with Leaf Discs. Rootlings of cv Cabernet Sauvignon were grown in a temperature-controlled glasshouse (27 C (11)]. Leaf material for experimental work was harvested when leaves first became fully expanded (young leaves) and at 3 months after full expansion (old leaves). Excised leaves were surface sterilized with sodium hypochlorite (6% available Cl2) and rinsed with sterile, distilled H20. All subsequent operations were done under aseptic conditions in a laminar flow cabinet. Discs (10 mm) were cut from the excised leaves and floated (abaxial surface uppermost) on 20 ml of test solution in sterile Petri dishes. There were four replicates of each treatment. Discs treated with test solutions were stored in a growth cabinet (27 C, 16-hr photoperiods, irradiance 10 wm-2). Illumination was provided by a 2:1 mixture of Gro-Lux E40 (Gro-Lux, Sylvania, Canada) and Osram MCFE (Osram, Australia) fluorescent tubes. All experiments commenced in the 12th hr of a photoperiod.Experiments with Excised Grape Berries. Specially propagated cuttings (13) were used to provide a supply of grape berries. The fruiting vines were grown as described above. Berries for experiments were excised approximately 1 da...

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