Graduate Thesis Or Dissertation
 

A study on the carotenoids of wild-type and mutant strains of the alga, Scenedesmus obliquus

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  • The primary objective of this thesis is to study, characterize and compare four types of Scenedesmus obliquus pigment mutants with the wild-type strain. The specific nature of the carotenoids synthesized in both heterotrophically and myxotrophically-grown cells, Hill reaction activity, photoreduction activity, and total photosynthetic activity of these cells are examined. Mutant C-X-6E, lacking carotenoids (dark-grown cells), bleaches when placed in the light; is unable to do photosynthesis; shows no Hill reaction; but does exhibit photoreduction activity. Another mutant, C-X -18, which has only high levels of acyclic carotenoids and low amounts of chlorophyll, also bleaches in the light and gives results similar to those seen in the photosynthetic studies with C-X-6E. C-X-6D, when grown in the dark, forms appreciable amounts of acyclic carotenoids and trace amounts of the cyclic and oxygenated carotenoids; when placed in the light it synthesizes normal carotenoids but retains the high levels of the acyclic carotenoids. This mutant shows very low levels of photos ystem II activity, low levels of photosystem I activity, and very low levels of overall photosynthesis. The final mutant studied, C-X-72, which has normal carotenoids and low levels of chlorophyll, is able to green in the light; exhibits low levels of photosystem I and II activity; and has a total photosynthetic activity lower than that of the wild-type. The results of these studies seem to indicate the close association between the carotenoids and the photosystem II and the necessity for a normal carotenoid biosynthetic pathway for the prevention of chlorophyll photooxidation and for maximum photosynthetic activity.
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