Seeds of Catharanthus roseus cv. Little Delicata were germinated in the dark which resulted in relatively high and even rates of germination. Analysis of alkaloids from the cotyledons of 6 - 9 day old dark grown seedlings led to the identification of tabersonine, 16-methoxytabersonine, and catharanthine as relatively major components while vindoline, deacetylvindoline, 4-desacetoxyvindoline and 16-hydroxytabersonine were identified as minor components. Subjecting dark grown seedlings to light led to a rapid increase in the amount of vindoline present with a concomitant decrease in the amounts of tabersonine, 16-methoxytabersonine and the minor components. The amount of catharanthine present was not greatly affected. These observations suggested that the biosynthetic pathway between tabersonine and vindoline proceeds as follows: 16-hydroxytabersonine → 16-methoxytabersonine → 16-methoxy-2,3-dihydro-3-hydroxytabersonine → 16-methoxy-2,3-dihydro-3-hydroxy-N(1)-methyltabersonine (i.e. desacetoxyvindoline) → deacetylvindoline → vindoline. © 1986.