The significance of xanthophylls and tocopherols in photo-oxidative stress and photoprotection of three Canarian laurel forest tree species on a high radiation day

Chloroplast pigments, chlorophyll fluorescence, and tocopherols in sun leaves of the Canarian laurel forest species Myrica faya, Laurus azorica, and Persea indica were characterized during the diurnal course of a high irradiation summer day. All species showed a de-epoxidation of the xanthophyll cycle and a decline of the photochemical efficiency of photosystem II measured as the Fv/Fm fluorescence ratio. Whereas in M. faya, decline and recovery of Fv/Fm was only correlated to zeaxanthin formation, these relations were divergent in L. azorica and P. indica. In P. indica, Fv/Fm did not fully recover until the next morning. Apparently, the decrease of Fv/Fm during the day reflected only a zeaxanthin-dependent, quickly recovering component in M. faya, but an additional component, probably due to photodamage processes requiring repair activities, was observed in L. azorica and P. indica. In leaves of those two species, α-tocopherol concentrations varied during the diurnal course, probably indicating active oxygen scavenging action. In P. indica leaves, a degradation and restoration of chlorophyll contents were observed during the day. The conclusion is that M. faya is most resistent to high light stress and P. indica most sensitive, which coincides with known ecological traits of these species.