Effects of green light supplementation with red and blue combinations of LED light spectrums on the growth and transcriptional response of Haematococcus pluvialis

Abstract

Light management strategy is crucial for improving microalgal production in terms of higher biomass and economically valuable bioactive molecules. However, green light has received less attention in developing light managements for algae and higher plant due to its low absorption rate by chlorophyll. In this study, the effects of green light supplementation, in the combination with red and blue light were investigated in Haematococcus pluvialis. 10% and 20% of green light supplementations were applied in 3:2 ratios of red and blue LED light combinations as an expense of red-light. Growth rates, chlorophyll concentration, and dry weight were measured to assess the growth kinetics of H. pluvialis along with the relative transcript accumulations of four mRNAs: Rubisco, PTOX₂, PsaB, and PsbS. Growth rates, chlorophyll concentrations and dry weight were found significantly higher in presence of 10% green light supplementation compared to red and blue light combinations. The relative transcript accumulations of Rubisco and PsbS genes showed significant upregulation at the end of the experiments (with the fold change of 42.91 ± 12.08 and 98.57 ± 27.38, respectively, relative to the beginning of the experiments) compared to combinations of red and blue light (fold change of 19.09 ± 3.0 and 47.77 ± 14.21, respectively, relative to beginning of the experiments). PsaB and PTOX₂ transcripts did not show significant accumulation differences between treatments. It seems that green light has a dose dependent additive effect on the growth rate of H. pluvialis. The upregulation of Rubisco and PsbS may indicate green light dependent carbon assimilation and light-harvesting response in H. pluvialis.