Occurrence of the lutein-epoxide cycle in mistletoes of the Loranthaceae and Viscaceae

Abstract

The lutein-epoxide cycle (Lx cycle) is an auxiliary xanthophyll cycle known to operate only in some higher-plant species. It occurs in parallel with the common violaxanthin cycle (V cycle) and involves the same epoxidation and de-epoxidation reactions as in the V cycle. In this study, the occurrence of the Lx cycle was investigated in the two major families of mistletoe, the Loranthaceae and the Viscaceae. In an attempt to find the limiting factor(s) for the occurrence of the Lx cycle, pigment profiles of mistletoes with and without the Lx cycle were compared. The availability of lutein as a substrate for the zeaxanthin epoxidase appeared not to be critical. This was supported by the absence of the Lx cycle in the transgenic Arabidopsis plant lutOE, in which synthesis of lutein was increased at the expense of V by overexpression of epsilon-cyclase, a key enzyme for lutein synthesis. Furthermore, analysis of pigment distribution within the mistletoe thylakoids excluded the possibility of different localizations for the Lx- and V-cycle pigments. From these findings, together with previous reports on the substrate specificity of the two enzymes in the V cycle, we propose that mutation to zeaxanthin epoxidase could have resulted in altered regulation and/or substrate specificity of the enzyme that gave rise to the parallel operation of two xanthophyll cycles in some plants. The distribution pattern of Lx in the mistletoe phylogeny inferred from 18S rRNA gene sequences also suggested that the occurrence of the Lx cycle is determined genetically. Possible molecular evolutionary processes that may have led to the operation of the Lx cycle in some mistletoes are discussed.

The impact of increased soil risk elements on carotenoid contents

“…It has also a direct role in nonphotochemical quenching through thermal dissipation [39] and it has been described that the xanthophyll cycle involving lutein operates together with the violaxanthin cycle [40][41][42][43][44]. It seems that SAG plants from polluted soil mitigated damage to their top leaves by higher utilization of lutein.…”

Sun-shade patterns of leaf carotenoid composition in 86 species of neotropical forest plants

“…At present, little is known about the regulation of epoxidation in the operation of the V cycle, and even less in the Lx cycle. Altered substrate specificity of the epoxidase enzyme to L has been suggested as a factor responsible for accumulation of Lx (Matsubara et al 2003). Different binding affinities of lightharvesting complexes to L and Lx ) could also play a role in distinct operation of the Lx cycle in different species.…”

Lutein from Deepoxidation of Lutein Epoxide Replaces Zeaxanthin to Sustain an Enhanced Capacity for Nonphotochemical Chlorophyll Fluorescence Quenching in Avocado Shade Leaves in the Dark

“…Since Bungard et al (1999), an additional xanthophyll cycle (the Lx cycle), involving the a-carotene pathway pigments lutein (L) and lutein epoxide (Lx), has been recognized in many diverse taxa (García-Plazaola et al, 2003;Matsubara et al, 2003Matsubara et al, , 2008.…”