Elevated Zeaxanthin Bound to Oligomeric LHCII Enhances the Resistance of Arabidopsis to Photooxidative Stress by a Lipid-protective, Antioxidant Mechanism

Abstract

The xanthophyll cycle has a major role in protecting plants from photooxidative stress, although the mechanism of its action is unclear. Here, we have investigated Arabidopsis plants overexpressing a gene encoding ␤-carotene hydroxylase, containing nearly three times the amount of xanthophyll cycle carotenoids present in the wild-type. In high light at low temperature wild-type plants exhibited symptoms of severe oxidative stress: lipid peroxidation, chlorophyll bleaching, and photoinhibition. In transformed plants, which accumulate over twice as much zeaxanthin as the wild-type, these symptoms were significantly ameliorated. The capacity of non-photochemical quenching is not significantly different in transformed plants compared with wild-type and therefore an enhancement of this process cannot be the cause of the stress tolerant phenotype. Rather, it is concluded that it results from the antioxidant effect of zeaxanthin. 80 -90% of violaxanthin and zeaxanthin in wildtype and transformed plants was localized to an oligomeric LHCII fraction prepared from thylakoid membranes. The binding of these pigments in intact membranes was confirmed by resonance Raman spectroscopy. Based on the structural model of LHCII, we suggest that the protein/lipid interface is the active site for the antioxidant activity of zeaxanthin, which mediates stress tolerance by the protection of bound lipids.

The xanthophyll cycle pool size controls the kinetics of non‐photochemical quenching in Arabidopsis thaliana

“…30% less NPQ in the sChyB plants compared to the wt. The final amplitude of NPQ obtained was not significantly different, even if the illumination period was extended (data not shown), as previously reported [16,17]. This was observed over a range of actinic light intensities from 50 to 2000 lmol photons m À2 s À1 (data not shown).…”

“…Plants exposed to excess light increase the size of the xanthophyll cycle pool [25][26][27], a response assumed to increase stress tolerance. Indeed, sChyB plants have a greater tolerance to photo-oxidative stress compared to wt plants as a result of the increased antioxidant activity from zeaxanthin [16,17]. However, such a beneficial effect of a larger xanthophyll cycle pool in sChyB plants left unexplained why the pool was not constitutively larger in the wild-type plants, since an altered expression of only one gene was involved.…”

“…The composition of carotenoids was determined by HPLC for leaf disks rapidly frozen in liquid N 2 [17]. To completely inhibit violaxanthin de-epoxidation, leaves were vacuum infiltrated with a 5 mM dithiothreitol (DTT) solution.…”

“…In order to further test this hypothesis it is necessary to determine whether these effects arise from changes in zeaxanthin concentration or from the change in ratio of zeaxanthin to violaxanthin, expressed as the de-epoxidation state (DES). Here we have used Arabidopsis plants in which the expression of the enzyme b-carotene hydroxylase 1 has been increased; these plants accumulate 2-3 times the level of violaxanthin with little perturbation of the content of other pigments [16,17]. Comparing these plants to wild-type plants we show that NPQ kinetics depend upon DES.…”

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.…”