Mutant lutein deficient

The most photosensitive part of the coleoptile with respect to phototropism is the apical 50 qm-zone. The first millimeter of the tip is 160 times more sensitive than the second, and the second millimeter 1,800 times more sensitive than the third 108h In 1937, Bunning29 showed by microchemical method that there is a high concentration of carotenoid (lutein) below the tip of the avena coleoptile, from 250 jum to 2 mm below this point and just in the extreme tip no carotenoid is found. This calls in question whether the enormous local differences in sensitivity can solely be caused by corresponding different absorption gradients. This doubt is further substantiated by the fact, that carotenoid deficient mutants (containing 5 to 10% of the normal siblings) show normal phototropic sensitivity. 

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... 

Connor, WE, Duell, PB, Kean, R, and Wang, Y, 2007. The prime role of HDL to transport lutein into the retina Evidence from HDL-deficient WHAM chicks having a mutant ABCA1 transporter. Invest Ophthalmol Vis Sci 48, 4226—4231. 

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). 

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