EPOXIDATION OF ZEAXANTHIN AND ANTHERAXANTHIN REVERSES NONPHOTOCHEMICAL QUENCHING OF PHOTOSYSTEM-II CHLOROPHYLL-A FLUORESCENCE IN THE PRESENCE OF TRANS-THYLAKOID DELTA-PH
Am. Gilmore et al., EPOXIDATION OF ZEAXANTHIN AND ANTHERAXANTHIN REVERSES NONPHOTOCHEMICAL QUENCHING OF PHOTOSYSTEM-II CHLOROPHYLL-A FLUORESCENCE IN THE PRESENCE OF TRANS-THYLAKOID DELTA-PH, FEBS letters, 350(2-3), 1994, pp. 271-274
The xanthophyll cycle apparently aids the photoprotection of photosyst
em IT by regulating the nonradiative dissipation of excess absorbed li
ght energy as heat. However, it is a controversial question whether th
e resulting nonphotochemical quenching is soley dependent on xanthophy
ll cycle activity or not. The xanthophyll cycle consists of two enzymi
c reactions, namely deepoxidation of the diepoxide violaxanthin to the
epoxide-free zeaxanthin and the much slower, reverse process of epoxi
dation. While deepoxidation requires a transthylakoid pH gradient (Del
ta pH), epoxidation can proceed irrespective of a Delta pH. Herein, we
compared the extent and kinetics of deepoxidation and epoxidation to
the changes in fluorescence in the presence of a light-induced thylako
id Delta pH. We show that epoxidation reverses fluorescence quenching
without affecting thylakoid Delta pH. These results suggest that epoxi
dase activity reverses quenching by removing deepoxidized xanthophyll
cycle pigments from quenching complexes and converting them to a nonqu
enching form. The transmembrane organization of the xanthophyll cycle
influences the localization and the availability of deepoxidized xanth
ophylls is to support nonphotochemical quenching capacity. The results
confirm the view that rapidly reversible nonphotochemical quenching i
s dependent on deepoxidized xanthophyll.