OXYGEN STRESS AND PIGMENT COMPOSITION IN CANARIAN LAUREL FOREST TREES

The pigment composition of the leaves of three evergreen tree species (Laurus azorica, Myrica faya and Persea indica) belonging to the canar ian laurel forest were determined in situ in the early morning and at midday. The ratio variable to maximal fluorescence (Fv/Fm) decreased a t midday in full sunlight to values of 0.7 in all species indicating p hotoinhibition. Together with depressions in Fv/Fm the shift in the xa nthophyll cycle was clear in all three species. No significant variati ons between the early morning and midday were found in the xanthophyll cycle pool. The degree in which this cycle was de-epoxidized at midda y had a trend to be larger in Myrica faya and Persea indica than in La urus azorica. No variation in neoxanthin and lutein content during the day was observed. The chlorophyll a/b ratio did not show significant differences between early morning and midday but a tendency towards ch lorophyll losses at midday could be found in all three species. The al pha-carotene/beta-carotene ratio did not vary along the day. The total carotene content was lower in Myrica faya which did not contain alpha -carotene. Studies along the year and under different stress condition s, including the study of the antioxidative system, are needed to have a clearer understanding of possible different patterns in these tree species on the protection of the photosynthetic apparatus against the excess of light.