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

Abstract

Leaves of avocado (Persea americana) that develop and persist in deep shade canopies have very low rates of photosynthesis but contain high concentrations of lutein epoxide (Lx) that are partially deepoxidized to lutein (L) after 1 h of exposure to 120 to 350 mmol photons m 22 s 21 , increasing the total L pool by 5% to 10% (DL). Deepoxidation of Lx to L was near stoichiometric and similar in kinetics to deepoxidation of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z). Although the V pool was restored by epoxidation of A and Z overnight, the Lx pool was not. Depending on leaf age and pretreatment, the pool of DL persisted for up to 72 h in the dark. Metabolism of DL did not involve epoxidation to Lx. These contrasting kinetics enabled us to differentiate three states of the capacity for nonphotochemical chlorophyll fluorescence quenching (NPQ) in attached and detached leaves: DpH dependent (NPQ DpH ) before deepoxidation; after deepoxidation in the presence of DL, A, and Z (NPQ DLAZ ); and after epoxidation of A+Z but with residual DL (NPQ DL ). The capacity of both NPQ DLAZ and NPQ DL was similar and 45% larger than NPQ DpH , but dark relaxation of NPQ DLAZ was slower. The enhanced capacity for NPQ was lost after metabolism of DL. The near equivalence of NPQ DLAZ and NPQ DL provides compelling evidence that the small dynamic pool DL replaces A+Z in avocado to "lock in" enhanced NPQ. The results are discussed in relation to data obtained with other Lx-rich species and in mutants of Arabidopsis (Arabidopsis thaliana) with increased L pools.

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

“…With ETR unchanged, persistent DL sustained higher NPQ DL that relaxed after assay with kinetics similar to NPQ DpH , in marked contrast to the slower relaxation of NPQ DLAZ . The light-saturated capacity for NPQ DL in similar experiments was approximately 80 per cent of that of NPQ DLAZ , and approximately 35 per cent greater than NPQ DpH attained in the absence of xanthophyll de-epoxidation [25]. Although xanthophyll-dependent and independent forms of NPQ may share a common mechanism [47], it is unclear at the physiological level how these capacities relate; does NPQ DLAZ for example, substitute for NPQ DpH or is it simply additive?…”

“…Designation of different forms of NPQ on the basis of kinetic responses in vivo follows the subscript conventions proposed previously [20,25]. Measurements of NPQ in pre-dawn assays, or from aluminium-foil shaded areas of exposed leaves, in the absence of deepoxidation of lutein epoxide (Lx) or V were considered to represent DpH-dependent processes (or qE) [26] and were designated NPQ DpH .…”

“…0.9), and deriving an estimate of t 1/2 from t 1/2 ¼ 0.693/k. We used the 'Vaseline patch' test [25] to confirm that stomata were closed in attached leaves pre-dawn and opened in approximately 30 min during induction in the shade (5 -20 mmol photons m 22 s 21 ).…”

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

“…A truncated form of this cycle, with very slow epoxidation of DL to Lx in the dark overnight or in the shade, has been extensively researched in the deeply shaded inner canopy of oaks (García-Plazoala et al 2003), of Inga spp. (Matsubara et al 2005(Matsubara et al , 2008 and in Laurus and Persea (avocado) (Esteban et al 2007(Esteban et al , 2008Förster et al 2009Förster et al , 2011) and other species. This interest in the truncated Lx-cycle arose because retention of DL after epoxidation of A + Z, allowed direct demonstration of the long suspected role for L in augmenting the capacity for NPQ, as detailed below.…”

“…data). Laboratory studies have ranged from the generation and evaluation of targeted carotenoid and xanthophyll cycle mutants of Arabidopsis (Pogson et al 1998) to natural selection of very high light resistant mutants of the model alga Chlamydomonas (Förster et al 2001(Förster et al , 2005 and to current research on these pigment inter-conversions in avocado canopies (Förster et al 2009(Förster et al , 2011.…”