Two xanthophyll cycles have been described in higher plants: the ubiquitous violaxanthin (V) cycle and the taxonomically restricted lutein epoxide (Lx) cycle. Both involve the light induced de-epoxidation of an epoxidated xanthophyll (V or Lx) and the epoxidation back in the dark. Evolutionary trends and function of the Lx cycle are still not clear. Up to nowadays, significant amounts of Lx have been found in several unrelated taxa, but it is a character almost exclusive from woody plants (except in the case of the parasitic plant Cuscuta reflexa). We have found an exception to this pattern in Cucumis sativus L., which showed high concentrations of Lx. Since Lx cycle was operative in leaves and cotyledons of this species and Lx concentration were much higher in cotyledons than in leaves, we speculate a role for the early stages of development. To date, this species is the first herbaceous non-parasitic species with operative Lx cycle. Since this species can be much more easily and rapidly grown and investigated than woody plants, these data can open new horizons and new lines of investigation for Lx cycle.
Keywords: cotyledon; cucumber; cucurbitaceae; lutein epoxide; violaxanthin; xanthophyll cycles.