title: Accumulation of Zeaxanthin in Abscisic Acid-Deficient Mutants of Arabidopsis Does Not Affect Chlorophyll Fluorescence Quenching or Sensitivity to Photoinhibition in Vivo.
abstract: Abscisic acid (ABA)-deficient mutants of Arabidopsis do not synthesize the epoxy-xanthophylls antheraxanthin, violaxanthin, or neoxanthin. However, thylakoid membranes from these mutants contain 3-fold more zeaxanthin than wild-type plants. This increase in zeaxanthin occurs as a stoichiometric replacement of the missing violaxanthin and neoxanthin within the pigment-protein complexes of both photosystem I and photosystem II (PSII). The retention of zeaxanthin in the dark by ABA-deficient mutants sensitizes the leaves to the development of nonphotochemical quenching (NPQ) during the first 2 to 4 min following a dark-light transition. However, the increase in pool size does not result in any increase in steady-state NPQ. When we exposed wild-type and ABA-deficient mutants leaves to twice growth irradiance, the mutants developed lower maximal NPQ but suffered similar photoinhibition to wildtype, measured both as a decline in the ratio of variable to maximal fluorescence and as a loss of functional PSII centers from oxygen flash yield measurements. These results suggest that only a few of the zeaxanthin molecules present within the light-harvesting antenna of PSII may be involved in NPQ and neither the accumulation of a large pool of zeaxanthin within the antenna of PSII nor an increase in conversion of violaxanthin to zeaxanthin will necessarily enhance photoprotective energy dissipation.
authors.affiliation: Cooperative Research Centre for Plant Science, Australian National University, G.P.O. Box 475, Canberra ACT 2601, Australia (V.H.).
authors.forename: V.
authors.initials: V
authors.lastname: Hurry
authors.forename: J. M.
authors.initials: JM
authors.lastname: Anderson
authors.forename: W. S.
authors.initials: WS
authors.lastname: Chow
authors.forename: C. B.
authors.initials: CB
authors.lastname: Osmond