Plastid development in albescent maize.

Plastid development in albescent (al/al) and wild-type (+/al) strains of Zea mays has been studied in the electron microscope. Etiolated seedlings of the mutant are severely deficient in colored carotenoid pigments and accumulate carotenoid precursors tentatively identified as phytoene and phytofluene. The fine structure of proplastids in etiolated wild-type and mutant leaves is similar with 1 notable exception. Osmiophilic bodies found in the wild-type were lacking in all sections of albescent proplastids examined suggesting that these structures may be storage centers for carotenoid pigments. Plastid pigments are destroyed, chlorophyll synthesizing potential is lost, and the ultrastructure of plastids is irreversibly altered when mutant seedlings are placed directly in high intensity light. However, synthesis of plastid pigments and development of the photosynthetic apparatus as seen in the electron microscope is normal, and indistinguishable from that in the wild-type, in seedlings of the albescent mutant preilluminated with low intensity light prior to high intensity illumination. During treatment in low intensity light carotenogenesis is initiated in the mutant and proceeds normally thereafter.