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. 2003 May;132(1):352-64.
doi: 10.1104/pp.102.019620.

Role of the reversible xanthophyll cycle in the photosystem II damage and repair cycle in Dunaliella salina

EonSeon Jin  1 , Kittisak Yokthongwattana, Juergen E W Polle, Anastasios Melis
Affiliations

Role of the reversible xanthophyll cycle in the photosystem II damage and repair cycle in Dunaliella salina

EonSeon Jin et al. Plant Physiol. 2003 May.

Abstract

The Dunaliella salina photosynthetic apparatus organization and function was investigated in wild type (WT) and a mutant (zea1) lacking all beta,beta-epoxycarotenoids derived from zeaxanthin (Z). The zea1 mutant lacked antheraxanthin, violaxanthin, and neoxanthin from its thylakoid membranes but constitutively accumulated Z instead. It also lacked the so-called xanthophyll cycle, which, upon irradiance stress, reversibly converts violaxanthin to Z via a de-epoxidation reaction. Despite the pronounced difference observed in the composition of beta,beta-epoxycarotenoids between WT and zea1, no discernible difference could be observed between the two strains in terms of growth, photosynthesis, organization of the photosynthetic apparatus, photo-acclimation, sensitivity to photodamage, or recovery from photo-inhibition. WT and zea1 were probed for the above parameters over a broad range of growth irradiance and upon light shift experiments (low light to high light shift and vice versa). A constitutive accumulation of Z in the zea1 strain did not affect the acclimation of the photosynthetic apparatus to irradiance, as evidenced by indistinguishable irradiance-dependent adjustments in the chlorophyll antenna size and photosystem content of WT and zea1 strain. In addition, a constitutive accumulation of Z in the zea1 strain did not affect rates of photodamage or the recovery of the photosynthetic apparatus from photo-inhibition. However, Z in the WT accumulated in parallel with the accumulation of photodamaged PSII centers in the chloroplast thylakoids and decayed in tandem with a chloroplast recovery from photo-inhibition. These results suggest a role for Z in the protection of photodamaged and disassembled PSII reaction centers, apparently needed while PSII is in the process of degradation and replacement of the D1/32-kD reaction center protein.

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Figures

Figure 1
Figure 1
Chl and Car content of D. salina cultures. The effect of growth irradiance on the cellular Chl content (A), total Car content (B), and Z content (C) of WT (white circle) and zea1 mutant (squares) is shown.
Figure 2
Figure 2
Effects of growth irradiance on de-epoxidation state of the xanthophyll cycle (A); PSII photochemical charge separation efficiency, as measured by the Chl fluorescence Fv/Fm ratio (B); Pmax of cellular photosynthesis (C); and Φ of photosynthesis (D) in WT (white circles) and zea1 mutant (squares) of D. salina.
Figure 3
Figure 3
Quantitative western-blot analysis of thylakoid membrane proteins from D. salina WT and zea1 mutant grown under different light intensities. Proteins were probed with specific polyclonal antibodies against the 160-kD PSII repair intermediate (A) or against the PSII D1/32-kD reaction center protein (B). The corresponding densitometric quantitations of the bands are given as a bar graph on the bottom of each panel. Lanes were loaded on an equal Chl basis (4 nmol Chl lane−1).
Figure 4
Figure 4
Quantitative western-blot analysis of thylakoid membrane proteins from D. salina WT and zea1 mutant grown under different light intensities. Proteins were probed with specific polyclonal antibodies raised against the LHC-II (A) and Cbr protein (B). The corresponding densitometric quantification of the bands is given as a bar graph on the bottom of each panel. Lanes were loaded on an equal Chl basis (4 nmol Chl lane−1).
Figure 5
Figure 5
Time course for the loss of the D1 protein from its 32-kD position after an LL → high light (HL) shift of the cultures. D. salina WT (white circles) and zea1 mutant (squares) were grown under LL to the late log phase. Cells were suspended in the presence of lincomycin immediately before an LL → HL shift. Western blots probed with polyclonal antibodies against the D1 protein are show in the upper panel. Densitometric quantification of the corresponding western blots for WT (white circles) and zea1 mutant (squares) are shown in the lower panel. The half time of the 32-kD protein loss was 32 ± 12 min for the WT and 45 ± 15 min for the zea1 mutant.
Figure 6
Figure 6
Time course of PS concentration (QA and P700) after an LL → HL shift of WT (white circles) and zea1 mutant (squares) of D. salina. A, Photochemically competent PSII measured from the amplitude of QA photoreduction. B, Photochemically competent PSI measured from the amplitude of P700 photoreduction.
Figure 7
Figure 7
Changes in the Pmax and Φ of photosynthesis after an LL → HL shift of the cultures. A, Measurement of the light-saturated rate of photosynthesis in WT (white circles) and zea1 mutant (squares). B, Measurement of the Φ in WT (white circles) and zea1 mutant (squares).
Figure 8
Figure 8
Changes in Pmax and Φ of photosynthesis after an HL → LL shift of the cultures. A, Measurement of the light-saturated rate of photosynthesis in WT (white circles) and zea1 mutant (squares). B, Measurement of the Φ in WT (white circles) and zea1 mutant (squares).
Figure 9
Figure 9
A, Comparative kinetic analysis of the accumulation of Z (solid circles), accumulation of photodamaged PSII reaction centers (solid diamonds), and loss of V (white circles) after an LL → HL shift of D. salina WT cultures. B, Decay kinetics of Z to V conversion after an HL → LL shift of the D. salina WT cultures.
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