Abstract:The increase of the differential absorbance at 505 nm(△A505) induced by highlight was measured in leaves of Aloe vera, Mangifera indica, Brassica chinensis, Sonchusoleraceus and unicellular green alga Dunaliella salina 1009. Absorbances of leaf discs andalga solution were measured directly by using a spectrophotometer after high light treatment. The differential absorbance was obtained from absorbent difference between thesamples under high light and in the dark. Leaves were collected at 8 a.m. and reservedin the dark to ensure the high content of violaxanthin. During the high lightl 500 μmol m-2S-1) exposure period, △A505, increased gradually in all tested plant species andDunaliella salina. The obvious increase of △505 could be found after short time exposure(5-10 min). The maximum of △A505 was observed during the time of exposure for 50 min depending on the species tested, then it slightly decreased. The presence of ascorbicacid stimulated the light-induced △A505 increment in Aloe leaves and Dunaliella cells. Theincrease of △A505 in illuminated leaves of Aloe and Sonchus disappeared during thesubsequent 5h-recovery in the dark. The result supported that △A505 is an useful and simpleindicator of in vivo violaxanthin de-epoxidation, and the xanthophyll cycle operates activelyin both higher and lower plants under high light condition. Red and white lights at thelevel of 1850 μmol m-2s-1 were chosen to irradiate the sample for comparing their effects on△A505 △A540 (light scattering, an indicator of energy state of chloroplast) as well as pigmentsand chlorophyll fluorescence of Dunaliella salina. These two light sources led to thedecrease of Fv/Fm, Fv/Fo and Fo, showing the characteristics of reversible photoinhibitionduring light exposure from 5 min to 90 min. No difference in pigment content or the ratiobetween chlorophyll and carotenoid was found under the two light sources. However, redlight showed less effect on PS II primary photochemical efficiency and △A505, but moreeffect on energy state as compared with white light.
