Capacity for chlorophyll synthesis in heat-bleached 70S ribosome-deficient rye leaves

Abstract

The leaves of young rye plants (Secale cereale L.) grown at 32° were deficient in chlorophyll and in chloroplastic rRNA as compared to those grown at 22°, which developed normally. Both chlorophyll accumulation and the formation of plastidic rRNA were largely restored at 32° when the plants were transfered several times for 1 h per day to 22°. In the chlorotic 32°-grown rye leaves the in vivo activity of δ-aminolevulinate synthetase was very low. Aminolevulinate dehydratase however, exhibited high activity in extracts from 32°-grown leaves and was localized in the plastid fraction isolated from the chlorotic leaf tissue. After application of δ-aminolevulinic acid to chlorotic parts of leaves growing at 32°, protochlorophyll(ide) was formed and accumulated in the dark. In the light, the protochlorophyll(ide) was photooxidized at 32°. The results suggest a cytoplasmic site of synthesis for the series of enzymes converting δ-aminolevulinate to protochlorophyll(ide). It is concluded that an inhibition of δ-aminolevulinate synthetase and the photooxidation of protochlorophyll(ide) or chlorophyll are responsible for the chlorosis of the leaves at 32°.