Xanthophyll deficient mutant

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... 

Prior to 1995, only one locus affecting Xanthophyll biosynthesis in photosynthetic tissues of Arabidopsis had been identified, the ABA i locus, the mutation of which disrupts zeaxanthin deepoxidase, one of two xanthophyll cycle enzymes (Koomneef et al, 1982 Rock and Zeevaart, 1991 Rock et al., 1992). As a step toward advancing understanding of xanthophyll biosynthesis, incorporation, and function in plants, the author s laboratory has screened for and identified mutations defining two additional loci required for xanthophyll biosynthesis in Arabidopsis, LUTl and LUT2 LUT= LUTein deficient). Mutations at either locus result in defects in the synthesis of lutein, the most predominant xanthophyll in plants. Singly and in combination with the aba mutation, these lut mutations have allowed the genetic construction of five distinct mutant lines which differ dramatically in their carotenoid composition relative to wild-type Arabidopsis. In the remainder of this chapter I will first briefly discuss the aba mutation followed by a... 

Chlamydomonas seems to be more similar to Scenedesmus than to Arabidopsis with respect to the consequences of j3-e carotenoid deficiency. In the lutl mutant, an increased Chi a b ratio indicates a partial defect in the assembly or stability of Chi a/b complexes (Eichenberger et al, 1986). However, at least some of the LHCII subunits are still assembled. Since these complexes are thought to contain lutein in the wildtype, this means that /S-carotene-type xanthophylls are probably able to replace lutein during the assembly and in stabilizing these complexes (Niyogi et al., 1997b). 

Chlamydomonas mutants have been isolated that are deficient either in violaxanthin de-epoxidase or zeaxanthin epoxidase. Using these mutants, it could be demonstrated that only part of the non-photochemical quenching observed in Chlamydomonas is dependent on the formation of zeaxanthin (Niyogi etal., 1997a). It will be interesting to see whether the absence of xanthophyll epoxidase or de-epoxidase products has an effect on the assembly of light-harvesting complexes in these mutants. 

Falbel TG, Staehelin LA and Adams WW III (1994) Analysis of xanthophyll cycle carotenoids and chlorophyll fluorescence in light intensity-dependent chlorophyll-deficient mutants of wheat and barley. Photosynth Res 42 , 191-202... 

Recent studies with the three ABA-deficient tomato mutants have contributed extensively to the clarification of the biosynthesis of ABA. These studies support the so-called indirect pathway of ABA biosynthesis in which the C40 xanthophyll violaxanthin is the likely precursor of ABA, with xanthoxin as an intermediate [22, 26]. It was concluded that the fic and sit mutations are impaired in the conversion of xanthoxin to ABA, and that the lesion in not is at a step between xanthoxin and violaxanthin. 

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