Macromolecular Physiology of Plastids

Publisher Website
Google Scholar
Abstract
The composition and amount of carotenoid pigments were determined in etiolated seedling leaves of 6 barley (Hordeum vulgare L.) mutants, comprising 1 xantha and 5 tigrina mutants. All mutants had on a mole basis approximately the same content of carotenoids as the wild type.The mutants xan‐u21, tig‐n32, and tig‐33 contained significantly higher amounts of carotenes than the wild type, ranging from 32 to 68% of the total carotenoid content as compared to the 4–8% found in the wild type. In the mutants tig‐b23 and tig‐o34, only a slight increase in the amount of carotenes was notable. The carotene content and composition in tig‐d12 was indistinguishable from that of the wild type.The carotenes extracted from xan‐u21, tig‐b23, tig‐n32, tig‐33, and tig‐o34 were characterized by adsorption chromatography and spectrophotometry. Mutant xan‐u21 is in the dark blocked in β‐carotene synthesis, and accumulates the aliphatic polyenes: phytofluene, proneurosporene, poly‐cis‐lycopenes, neo‐lycopene and lycopene. The other four mutants synthesize β‐carotene, but accumulate in addition various higher saturated carotenes, the main components being ζ‐carotene in tig‐b23, a lycopenic pigment in tig‐n32 and tig‐33, and lycopene in tig‐o34.Accumulation of higher saturated carotenes appears correlated with specific aberrations of the membrane structure in plastids. The regulation of carotene and protochlorophyllide syntheses in etioplasts are closely linked as shown by the single gene mutants which affect both pathways. However, several mutants have been identified which cause defects in protochlorophyllide synthesis only.