Light activation of vindoline biosynthesis does not require cytomorphogenesis in Catharanthus roseus seedlings

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 decarboxyl ase (TDC) and desacetoxyvindoline 4-hydroxylase (D4H), which catalyse the f irst and penultimate reactions of vindoline biosynthesis, was identified by immunocytochemistry in developing seedlings. The expression of TDC was res tricted to the upper epidermis of cotyledons, whereas that of D4H was confi ned to laticifer cells. Light exposure of etiolated seedlings significantly induced D4H enzyme activity without changing the steady-state levels of D4 H immunoreactive protein or modifying the cellular distribution of D4H expr ession in dark-grown seedlings. These results suggest that the early and la te stages of vindoline biosynthesis occupy different cellular compartments, even in the early phases of etiolated seedling development. The role of li ght in activating the late stages of vindoline biosynthesis does not, there fore, seem to be related to the formation of the laticifer and idioblast ce ll types. It is concluded that light is not required for formation of these cell types, whereas regulatory factors, restricted to idioblasts and latic ifers, may respond to light to activate localised expression of the late st ages of vindoline biosynthesis. (C) 2000 Elsevier Science Ltd. All rights r eserved.