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Upon illumination, the cotyledons of Catharanthus roseus seedlings readily synthesise vindoline from late biosynthetic intermediates, which accumulate in etiolated seedlings. The cellular localisation of tryptophan decarboxylase (TDC) and desacetoxyvindoline 4-hydroxylase (D4H), which catalyse the first and penultimate reactions of vindoline biosynthesis, was identified by immunocytochemistry in developing seedlings. The expression of TDC was restricted to the upper epidermis of cotyledons, whereas that of D4H was confined to laticifer cells. Light exposure of etiolated seedlings significantly induced D4H enzyme activity without changing the steady-state levels of D4H immunoreactive protein or modifying the cellular distribution of D4H expression in dark-grown seedlings. These results suggest that the early and late stages of vindoline biosynthesis occupy different cellular compartments, even in the early …