Effects of light quality on the photosynthetic activity and biochemical composition of Gracilaria gracilis (Rhodophyta)

Different light qualities, i.e. ultraviolet (280-400 nm), blue (400-450 nm), green (500-550 nm) and red (620-670 nm) were combined with the actinic yellow light (SOX) (590 nm) under saturation of photosynthetic activity conditions, in order to consider the specific effects of each waveband on the red macroalga Gracilaria gracilis physiology. In this context, the fluctuation of biomass production, photosynthetic activity estimated as in vivo chlorophyll a fluorescence, protein and pigment contents, polyphenol concentration, antioxidant activity and the content and composition of the mycosporine-like amino acids (MAAs)-UV-absorbing compounds were studied. After 3 days of culture, the supplemented light had not induced any variation in photosynthetic pattern compared to the control (only SOX light). However, after 2 weeks of culture, supplemented blue light stimulated the accumulation of phenolic compounds which reached a value of 2.92 +/- 0.22 mg g(-1) DW, 68% higher than the control. Moreover, supplemented green light induced the accumulation of proteins and R-phycoerythrin (R-PE), i.e. 29 +/- 4.32 mg g(-1) DW and 0.91 +/- 0.34 mg g(-1) DW, respectively, being an increase of 56% and 78%, respectively, compared to the control. Red light boosted the growth rate, i.e. 7.24% +/- 1.06 compared to the control which was 2.17% +/- 0.2. Finally, UV radiation induced a marked increase of MAAs reaching 133.03 +/- 41.54 mg g(-1) DW, 162% higher content than the one in the control. The use of supplemented light of specific wavelengths to a saturated light irradiance for photosynthesis as an effective approach to increase the content of bioactive compound for biotechnology application is concretely discussed.