Xanthophyll double mutants

Chlamydomonas reinhardtii double mutant npq2/lorl lacks the P,e-carotenoids lutein and loroxanthin as well as all P,P-epoxycarotenoids derived from zeaxanthin (e g. violaxanthin and neoxanthin). Thus, the only carotenoids present in the thylakoid membranes of the npq2/lorl cells are P-carotene and zeaxanthin. The effect of these mutations and the lack of specific xanthophylls on the Chi antenna size of the photosystems was investigated [16]. In cells of the mutant strain, the Chi antenna size of PSII was substantially smaller than that of the wild type (Table 1). In contrast, the Chi antenna size of PSI was not truncated in the mutant. This analysis showed that absence of lutein, violaxanthin and neoxanthin specifically caused a smaller functional Chi antenna size for PSII but not for that of PSI. Thus, xanthophyll-bios5mthesis genes, such as lycopene e-cyclase and zeaxanthin epoxidase may be targets for a truncated Chi antenna size in PSII. 

The occurrence of xanthophyll dioxygenase, which releases xanthoxin from xanthophyll, was found using the ABA-deficient mutant vpl4oi Z. mays.650 Xanthophyll dioxygenase cleaves the double bond between C-ll (C-11 ) and C-12 (C-12 ) of 9-Z-violaxanthin (43) and 9 -Z-neoxanthin to give xanthoxin (5).651 The mRNA of xanthoxin dioxygenase in the leaves of P. vulgaris increased upon water stress and decreased upon... 

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