High light-induced changes of the differential absorbance at 505 nm and chlorophyll fluorescence in leaves and in green alga Dunaliella salina.
Lin ZhiFang, Peng ChangLian, Lin GuiZhu, Chen ShaoWei
Author Affiliation: South China Institute of Botany, Academy Sinica, Guangzhou 510650, China.
Journal of Tropical and Subtropical Botany 5 : 27-34
Abstract : The increase of the differential absorbance at 505 nm (?A505) induced by high light was measured in leaves of Aloe vera [A. barbadensis], Mangifera indica, Brassica chinensis, Sonchus oleraceus and unicellular green alga Dunaliella salina 1009. Absorbances of leaf discs and alga solution were measured directly by using a spectrophotometer. The differential absorbance was obtained from absorbent difference between the samples under high light and in the dark. Leaves were collected at 08.00 h, and were maintained in the dark to ensure the high content of violaxanthin. During high light (1500 µmol m-2s-1) exposure, ?A505 increased gradually in all tested species. The highest increase in ?A505 occurred after 5-10 minutes exposure. Depending on the species, the maximum ?A505 was observed after 30-50 minutes. The presence of ascorbic acid stimulated light-induced ?A505 increase in A. barbadensis leaves and in D. salina cells. The increase in ?A505 in illuminated leaves of A. barbadensis and Sonchus disappeared during a subsequent 5 h dark period. It is suggested that ?A505 is a useful indicator of in vivo violaxanthin de-epoxidation, and that the xanthophyll cycle operates actively in higher and lower plants under high light conditions. Red and white lights at 1850 µmol m-2s-1 were used to irradiate the sample, and their effects on ?A505, ?A540 (light scattering, an indicator of energy state of chloroplast), pigments and chlorophyll fluorescence of D. salina, were investigated. These 2 light sources led to decreases in Fv/Fm, Fv/Fo and Fo, suggesting reversible photoinhibition during light exposure from 5 to 90 min. No differences in pigment contents or the chlorophyll:carotenoid ratio occurred between the 2 light sources. However, red light had less effect on PS II primary photochemical efficiency and ?A505, but had more effect on the energy state than white light.