PLANT PHYSIOLOGY , Vol 108, Issue 4 1657-1664, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Isolation and Characterization of a Protein Associated with Carotene Globules in the Alga Dunaliella bardawil
A. Katz, C. Jimenez and U. Pick
Department of Biochemistry, the Weizmann Institute of Science, Rehovot, Israel 76100 (A.K, U.P)
The halotolerant alga Dunaliella bardawil accumulates very large amounts of
[beta]-carotene when exposed to high light intensity. The accumulated
[beta]-carotene is concentrated in small, oily globules within the
chloroplast and has been suggested to protect the alga against photodamage
by high irradiation (A. Ben-Amotz, A. Katz, M. Avron [1982] J Phycol
18:529-537;A. Ben-Amotz, M. Avron [1983] Plant Physiol 72: 593-597; A.
Ben-Amotz, A. Shaish, M. Avron [1989] Plant Physiol 91: 1040-1043). A 38-kD
protein was identified and purified from [beta]-carotene globules and was
designated carotene globule protein (Cgp). Induction of Cgp occurs in
parallel with [beta]-carotene accumulation in D. bardawil grown under
different inductive conditions. Cgp is overproduced in a constitutive
mutant strain that overproduces [beta]-carotene and is not detected in
Dunaliella salina, a species that does not accumulate [beta]-carotene. Cgp
production was not suppressed by norflurazon, an inhibitor of
[beta]-carotene synthesis that leads to accumulation of the carotenoid
precursor phytoene. Immunogold-labeling analysis by electron microscopy
demonstrates that the protein is localized at the periphery of the
globules. Proteolytic cleavage by trypsin enhances the coalescence and
destruction of the globules, in parallel with Cgp disappearance. It is
suggested that the function of Cgp is to stabilize the structure of the
globules within the chloroplast.
