3 (violaxanthin, zeaxanthin and antheraxanthin) participate in series of photo-induced interconversions known as ''violaxanthin cycle''; Xanthophyll; a carotene epoxide that is precursor to capsanthin; cleavage of 9-cis-epoxycarotenoids (violaxanthin) to xanthoxin, catalyzed by 9-cis-epoxycarotenoid dioxygenase, is the key regulatory step of abscisic acid biosynthesis; one of 3 xanthophylls involved in evolution of plastids of green plants (oxygen evolution)