Fig. 3 Daily course of the xanthophyll photoprotective system in cotton under field conditions (adapted from Björkman and Demmig-Adams, 1994). (Top) Incident PFD, efficiency of PSII, and fraction of PSII centers that were closed. This amount of closure is much less than would occur without intervention of the xanthophyll cycle. (Bottom) Concomitant changes in concentrations of xanthophyll pigments during the day as violaxanthin was converted to zeaxanthin, which is capable of accepting excitation energy from chlorophyll
