Another possible difficulty with a reverse genetic approach is that many of the genes involved in nutrient mobilization are likely to have important housekeeping functions (i.e. these genes may be generally required for nutrient transport throughout the life of the plant). RAN1 appears to be such a gene. As described here, RAN1 is required for normal devel- opment of the adult rosette. The various pleiotropic effects of the ran1-4 mutation preclude analysis of nutrient mobilization during senescence in the mutant. One way to rescue non- senescent phenotypes might be to use chimeric promoter/ gene constructs. In a transgenic plant, a housekeeping gene could be expressed under the control of the CAB promoter or similar promoter expressed prior to senescence. It is well established that the CAB promoter drives expression in photo-