Effects of changes of irradiance on the pigment composition of Gracilaria tenuistipitata var. liui Zhang et Xia

In plants, excess irradiation can damage the photosynthetic apparatus, although some protective mechanisms exist. The excess energy can be dissipated as thermal energy, and pigments (i.e., carotenoids) also play an important role in protecting the photosynthetic apparatus by epoxidating reactions. Chromatographic analysis of pigment extracts of Gracilaria tenuistipitata shows that zeaxanthin is the major carotenoid in this alga, accounting for up to 82% of total carotenoids. Short-term (55 h) and long-term (10 days) response of the pigments shows that Chi a, beta-carotene and zeaxanthin degradation after light increase follows negative exponential trends, while the response of biliproteins is almost linear. Decreasing the irradiance results in a clear saturating response of the synthesis of Chi a and beta-carotene after one to two days. Biliprotein synthesis displays a double linear trend, the first one lasting for four days in the cases of both R-phycoerythrin (RPE) and R-phycocyanin (RPC). The response of zeaxanthin is always faster than that of Chi a or biliproteins to changes of irradiance. Our results might indicate the presence of two pools of zeaxanthin in this alga, with different acclimation responses to the changes in the photon flux density. (C) 1999 Elsevier Science S.A. All rights reserved.