“… carotenoids observed with … inhibited by Mn 2+ (MnCl 2 or MnSO 4 ) as well as by some inhibitors of the Hill reaction such as dichlorophenyl-1,1-dimethylurea (…,6-bis-isopropylamino- s -triazine and o -phenanthroline or by reducing agents such as ascorbate plus tetramethyl- p -phenylene diamine (TMPD).”