Relationship between the Inhibitory Effects of 5,6–Epoxyxaiithophylls and Phototropism

Using a range of assay systems, the effect of light on the inhibitory properties of several carotenoids were investigated. The 5,6‐epoxyxanthophylls: violaxanthin, neoxanthin and 5,6‐monoepoxylutein when illuminated were shown to cause inhibition in the various assays, while a certain amount of inhibition also occurred with the dark treatment. The suggestion that phototropism might be the result of light induced formation of inhibitory compounds was also investigated and there was no evidence that the inhibitors obtained by in vitro degradation of 5,6‐epoxyxanthophylls play a part in phototropism.