Lutein Accumulation in the Absence of Zeaxanthin Restores Nonphotochemical Quenching in the Arabidopsis thaliana npq1 Mutant  

Abstract

Plants protect themselves from excess absorbed light energy through thermal dissipation, which is measured as nonphotochemical quenching of chlorophyll fluorescence (NPQ). The major component of NPQ, qE, is induced by high transthylakoid DpH in excess light and depends on the xanthophyll cycle, in which violaxanthin and antheraxanthin are deepoxidized to form zeaxanthin. To investigate the xanthophyll dependence of qE, we identified suppressor of zeaxanthinless1 (szl1) as a suppressor of the Arabidopsis thaliana npq1 mutant, which lacks zeaxanthin. szl1 npq1 plants have a partially restored qE but lack zeaxanthin and have low levels of violaxanthin, antheraxanthin, and neoxanthin. However, they accumulate more lutein and a-carotene than the wild type. szl1 contains a point mutation in the lycopene b-cyclase (LCYB) gene. Based on the pigment analysis, LCYB appears to be the major lycopene b-cyclase and is not involved in neoxanthin synthesis. The Lhcb4 (CP29) and Lhcb5 (CP26) protein levels are reduced by 50% in szl1 npq1 relative to the wild type, whereas other Lhcb proteins are present at wild-type levels. Analysis of carotenoid radical cation formation and leaf absorbance changes strongly suggest that the higher amount of lutein substitutes for zeaxanthin in qE, implying a direct role in qE, as well as a mechanism that is weakly sensitive to carotenoid structural properties.

Snapshot Transient Absorption Spectroscopy of Carotenoid Radical Cations in High-Light-Acclimating Thylakoid Membranes

“…7,8 In addition to Zea, the carotenoid lutein (Lut) is thought to be directly involved in quenching via similar mechanisms. 9,10 In previous work, the Zea radical cation (Zea •+ ) was observed in high-light-acclimated plant thylakoids using transient absorption (TA) spectroscopy. 6 However, these thylakoids had been high-light-acclimated for over 30 min before measurement, which does not indicate whether CT quenching is activated within the first few minutes of high light exposure, the time scale of qE activation.…”

Carotenoids in nature: insights from plants and beyond

“…In addition, the luminal pH and ascorbate content appear to affect post-translation modulation of VDE activity and is critical for determining the levels of zeaxanthin upon exposure to excessive light (Rockholm and Yamamoto 1996). Further, the bLCY mutant (suppressor of zeaxanthin-less1, szl1) lacks zeaxanthin, yet accumulates higher levels of lutein and a-carotene, which partially restores quenching efficiency, revealing that lutein could substitute for zeaxanthin (Li et al 2009a). The modulation of zeaxanthin levels by the violaxanthin de-epoxidase (VDE) is thought to be required for the thermal dissipation of excess light energy and the protection of photosynthetic membranes against lipid peroxidation, a process known as the xanthophyll cycle (Havaux and Niyogi 1999).…”

Canopy conundrums: building on the Biosphere 2 experience to scale measurements of inner and outer canopy photoprotection from the leaf to the landscape

“…Moreover, these ecophysiological studies with leaves of woody plants in the field and controlled environments provided the first direct evidence for the long suspected possibility that L, like A and Z has a role in photoprotection. They presaged recent biophysical studies showing engagement of NPQ in a Z-free, L overexpressing Arabidopsis mutant generates a cation radical analogous to that arising from Z in other mutants (Li et al 2009). …”

“…It seems likely that the xanthophylls are associated with structural changes in major light harvesting complexes (de Bianchi et al 2010) that produce populations of more rapidly quenching antenna complexes (Gilmore et al 1998;Li et al 2002) and dissipate excitation before transfer to reaction centres. Arabidopsis mutants have been constructed to show that Z and L produce similar radical cations (quenching centres) when NPQ is engaged (Li et al 2009) and the equivalence of A and DL sustained NPQ in avocado leaves has been explored using fluorescence lifetime imaging (Matsubara et al 2011).…”