Chromoplast development in a carotenoid mutant of maize

Summary The lethal recessive mutantlycopenic in maize is characterized by the synthesis of lycopene instead of the normal carotenoids. At normal conditions of illumination it loses chlorophyll by photo-oxidation. Seedlings of this mutant and of normal maize were grown at light intensities of 25–30 lux and 500–30,000 lux. Their plastid development was studied by electron microscopy.At low light intensities a kind of mesophyll chloroplast with elongated grana, long unpaired thylakoid segments, and sometimes prolamellar bodies is formed in mutant plants. In corresponding bleached plants the plastids are transformed into chromoplasts containing characteristic lycopene crystalloids similar to those found in tomato fruits. Various stages in this chromoplast development are described and illustrated. Also bundle-sheath plastids were found to develop into chromoplasts.It is concluded that the ultrastructure of plastids in a tissue is influenced by the nature of their pigments and that an altered carotenoid composition therefore can give rise to development of chromoplasts in plants which normally lack such organelles.