Growth, pigment composition, chlorophyll fluorescence and antioxidant defenses in the red alga Gracilaria lemaneiformis (Gracilariales, Rhodophyta) under light stress

• The growth strategy of Gracilaria lemaneiformis under different light intensities were studied.
• Positive effect of growth and pigment synthesis under high light intensity were founded in these studies.
• The chlorophyll fluorescence levels decreased under low light intensity.
• The SOD and CAT activities levels increased under low light intensity.
• There must be some relationships between the activity of antioxidant enzymes and pigment content or chlorophyll fluorescence value.

To investigate the response of the Gracilaria lemaneiformis (Gracilariales, Rhodophyta) to light stress, algae were grown at low (LL), intermediate (IL), and high light (HL) conditions. The relationship between photoacclimatory plasticity, light energy utilization and antioxidant capacity, and many physiological and biochemical parameters, including growth rate, pigment composition, ratio of variable fluorescence to maximum fluorescence (Fv/Fm), photochemical quenching coefficient (qP), non-photochemical quenching coefficient (NPQ), superoxide dismutase (SOD) and catalase (CAT) were determined in this study. With the increase in light intensity from LL to HL, the RGR, Chl a, Car contents, and maximal photochemical efficiency of photosystem II (PSII) increased significantly at 72 h and 120 h. However, algae growing at LL exhibited reduced photochemical efficiency of PSII and physiological activity as compared to that at HL, that is characterized by NPQ, SOD and CAT enhancement, but Chl a measuring at LL was significant higher than that at IL. Meanwhile, high Chl a value was also observed at HL after 72 h and 120 h culture compared with that at ML. The results suggest that under the low light irradiance, the G. lemaneiformis performed a negative vegetal and physiological strategy for adapting the environmental stress via regulating PSII reaction centers normalization and ROS metabolization, and so forth.