THE FATE OF CHLOROPLAST PIGMENTS DURING SENESCENCE OF PRIMARY LEAVES OF HORDEUM-VULGARE AND AVENA-SATIVUM

The fate of chloroplast pigments during senescence of detached primary leaves of Hordeum vulgare L. and Avena sativum L. has been studied. In both species, the carotenoids were lost at a much slower rate than the chlorophylls, with chlorophyll a being lost at a slightly faster rate than chlorophyll b. A detailed examination of the pattern of carotenoid destruction by high performance liquid chromatography revealed, however, that different processes were taking place in the two species. In H. vulgare, beta-carotene levels were reduced to approximately 40 % of their original levels whereas the xanthophylls (lutein, violaxanthin and neoxanthin) were reduced to between 8 % and 16 % of their original levels. Violaxanthin and neoxanthin were particularly susceptible to the oxidative processes involved in senescence. In A. sativum lutein was the most stable carotenoid and both neoxanthin and beta-carotene were readily destroyed. In both species quite high levels of xanthophyll acyl esters, accounting for up to 60 % of total carotenoid, were detected in the leaves, especially in the late stages of senescence. Plastoglobuli isolated from H. vulgare contained equivalent amounts of unesterified lutein and beta-carotene together with small amounts of xanthophyll acyl esters. Chlorophylls were present in only trace amounts in the plastoglobuli. Similar patterns of pigment destruction were seen in detached leaves and intact seedlings.