Formation of chloroplast pigments and sterols in rye leaves deficient in plastid ribosomes

Abstract

1. In rye (Secale cereale L.) leaves the formation of plastidic ribosomes is sensitive to elevated growth temperatures. Parallel to the loss of 70S ribosomes, in leaves growing at 32° chlorophyll accumulation was also prevented. Except for the tips of the first leaves which still contained some 70S ribosomes, the leaves were chlorotic. The amount of chlorophyll formed at 32° depended on the light intensity and decreased with higher intensities. After return to normal temperature (22°) chlorotic parts of the first leaves greened to a varying extent while those parts of most 2. or 3. leaves which had been formed in light at 32° remained permanently bleached until they died. Those parts of 2. and 3. leaves which were newly formed at 22° became normally green again. - 2. Formation and distribution of total and individual carotenoids were compared after development at 22° and 32°. In dark-grown leaves the higher growth temperature had no marked influence on the quantity or composition of carotenoids. At 22° the content of total carotenoids was 5fold and that of β-carotene 25fold increased by light. At 32° these light-induced increases were much lower. Only 41% of the total carotenoids and 18% of the β-carotene formed at 22° in light were found at 32°. Of the carotenoids present at 32°, 76% were located in the light green tips of the leaves. In plastids isolated from completely chlorotic leaf parts, carotenoids were still present and were even the predominant pigments. - 3. The contents of total sterols, the fractions of free sterols, sterol glycosides and esters, and the composition of individual sterols were compared in rye leaves grown at 22° and at 32°, in light or darkness. Light had little effect on the total sterol contents per leaf. However, more than 2fold higher sterol contents were observed in leaves grown at 32°, as compared to those from 22°. The amounts of most sterol fractions and individual sterols were similarly increased at the higher temperature but the sterol glycosides being relatively more increased than the total sterols.