Zeaxanthin Has Enhanced Antioxidant Capacity with Respect to All Other Xanthophylls in Arabidopsis Leaves and Functions Independent of Binding to PSII Antennae

Abstract

The ch1 mutant of Arabidopsis (Arabidopsis thaliana) lacks chlorophyll (Chl) b. Leaves of this mutant are devoid of photosystem II (PSII) Chl-protein antenna complexes and have a very low capacity of nonphotochemical quenching (NPQ) of Chl fluorescence. Lhcb5 was the only PSII antenna protein that accumulated to a significant level in ch1 mutant leaves, but the apoprotein did not assemble in vivo with Chls to form a functional antenna. The abundance of Lhca proteins was also reduced to approximately 20% of the wild-type level. ch1 was crossed with various xanthophyll mutants to analyze the antioxidant activity of carotenoids unbound to PSII antenna. Suppression of zeaxanthin by crossing ch1 with npq1 resulted in oxidative stress in high light, while removing other xanthophylls or the PSII protein PsbS had no such effect. The tocopherol-deficient ch1 vte1 double mutant was as sensitive to high light as ch1 npq1, and the triple mutant ch1 npq1 vte1 exhibited an extreme sensitivity to photooxidative stress, indicating that zeaxanthin and tocopherols have cumulative effects. Conversely, constitutive accumulation of zeaxanthin in the ch1 npq2 double mutant led to an increased phototolerance relative to ch1. Comparison of ch1 npq2 with another zeaxanthinaccumulating mutant (ch1 lut2) that lacks lutein suggests that protection of polyunsaturated lipids by zeaxanthin is enhanced when lutein is also present. During photooxidative stress, a-tocopherol noticeably decreased in ch1 npq1 and increased in ch1 npq2 relative to ch1, suggesting protection of vitamin E by high zeaxanthin levels. Our results indicate that the antioxidant activity of zeaxanthin, distinct from NPQ, can occur in the absence of PSII light-harvesting complexes. The capacity of zeaxanthin to protect thylakoid membrane lipids is comparable to that of vitamin E but noticeably higher than that of all other xanthophylls of Arabidopsis leaves.

Economic photoprotection in photosystem II that retains a complete light-harvesting system with slow energy traps

“…The asLhcb2 mutant showed slower kinetics than the WT, corresponding to a smaller cross-section (57% that of the control on average). The cross-section measured for the Ch1 leaf was only 23% that of the WT value, which is in good agreement with calculations based on biochemical data (see Table 1) and with a previous report 18 . According to our model-based results, the WT leaf consisted of two main pools of PSII, a large one (B400 chlorophylls per RC) besides a smaller pool of PSII supercomplexes, in agreement with the acknowledged existence of PSII centres with distinct photosynthetic unit sizes (the so-called a-and b-species of PSII 16 ).…”

“…The former mutant possesses a halved PSII antenna compared with the WT 17 , while Ch1 has no major LHCII and only expresses one monomeric antenna complex 18 . Taking into account that our WT plants formed B5 LHCII trimers per one RCII 19 , it was possible to predict, on a biochemical basis 20,21 , that the chlorophyll content of the Ch1 antenna was B22% that of the wild-type (Table 1, 'Estimated cross-section' column).…”

From ecophysiology to phenomics: some implications of photoprotection and shade–sun acclimation in situ for dynamics of thylakoids in vitro

“…These studies focus renewed attention on the roles of L in addition to its primary function as the most effective xanthophyll quencher of triplet Chl when occupying the L1 and L2 positions in LHCII [60]. Although there seems little likelihood that L substitutes for Z in protection against 1 O 2 [39,40], the causes of, and the significance of, an initial net loss of L in avocado shade leaves on exposure to sunlight remain enigmatic.…”

Singlet Oxygen Is the Major Reactive Oxygen Species Involved in Photooxidative Damage to Plants

“…Because we observed high levels of 1 O 2 -mediated LPO in the vte1 npq1 mutant that directly preceded or occurred concurrently with cell death we hypothesized that 1 O 2 produced by the photosystems is also cytotoxic, damaging the photosynthetic tissues. To validate this hypothesis, we assessed LPO events in ch1 mutant plants that are deficient in chlorophyll b and PSII chlorophyllprotein antenna complexes and are characterized by a low nonphotochemical quenching (NPQ) capacity (Havaux et al, 2007). Because NPQ deactivates excited chlorophylls, thereby avoiding 1 O 2 production, its inhibition in ch1 leads to a highly sensitive photooxidation phenotype.…”

“…lines were issued from the Columbia ecotype (Col-0). The vte1 npq1, ch1, and Cat(2) plants have been previously described (Vandenabeele et al, 2004;Havaux et al, 2005Havaux et al, , 2007. They were cultivated on soil under low light (100 mmol m 22 s 21 ; day/night 8/16; 20°C/18°C; 70% relative humidity) and normal (380 ppm) or high CO 2 (2,000 ppm) for 4 to 5 weeks.…”