Changes in Ultrastructure and Pigment Content During Development and Senescence of Fruits of Normal and rin and nor Mutant Tomatoes

Fruits of the normal Rutgers tomato cultivar and of the rin and nor mutants were examined at the following times: Rutgers at 17, 21, 32, 45, 47, 50 and 55 days after anthesis; rin and nor at 17, 21, 32, 50, 65, 78 and 95 days after anthesis. Ripening in Rutgers fruits began at about 47 days, and fruits were fully ripe by 55 days after anthesis. Full size was reached in both Rutgers and in the mutant fruits about 50 days after anthesis. Rin fruits subsequently turned yellow, and nor fruits developed some pink colour, but the fruits of both mutants remained sound and comparatively firm for up to 95 days after anthesis. No unique differences in ultrastructure were noted between Rutgers and mutant fruits except that myelin figures were observed in 21- and 32-day nor fruits and spiral membrane tubules were found in the epidermis of 95-day rin fruits. In Rutgers fruits, the major change was the transformation of chloroplasts to chromoplasts during ripening; this transformation was completed within 5 days. A similar, but much slower and less complete, transformation was noted in the mutants. Some grana and chlorophyll were present even in 95-day fruits, although rin and nor fruits began to lose chlorophyll and to accumulate coloured carotenoids from the time the fruits reached full size. The slow changes in ultrastructural transformation of plastids, paralleled by the changes in colour, suggest either suppression of nuclear action or lack of capacity to produce cellular components essential for normal ripening. The latter suggestion was favoured by current information on the physiology of the mutants.