Non-Photosynthetic Roles of Cyanobacterial Phytochromes in Spirulina (Arthrospira platensis), as Affected by Different Light Colors

BACKGROUND AND OBJECTIVESNowadays, spirulina is one of the most important cyanobacteria that is used as a food-drug supplement. The effect of light color on the growth of spirulina has also been studied in some previous studies. Also, the medicinal and useful properties of phycobilins as cyanobacterial phytochromes have been reported previously. On the other hand, unlike plant phytochromes, phycobilins are better known for their photosynthetic roles in phycobilisomes. In this research, the effects of light color on growth, pigment content and especially the non-photosynthetic roles of phytochromes in spirulina have been studied.MATERIALS AND METHODSCultivation of Spirulina (Arthrospira platensis) in glass containers with a volume of ۵۰۰ ml, without aeration and under continuous light (۱۵۰۰ lux/m۲) for ۴۵ days at ۲۲ to ۲۵ degrees Celsius was carried out in a randomized complete block design in ۴ replications. The light colors were provided by LED lamps and included white as control, yellow, red, green and blue color. The measured traits included the rate of growth and fresh weight, the content of non-phytochrome pigments, including chlorophyll a, total carotenoids, as well as the amounts of phytochromes including phycocyanin, allophycocyanin and phycoerythrin on one hand and the ratio between pigments on the other hand.RESULTS AND DISCUSSIONBased on the results, the effect of light color on growth was significant and the highest growth was obtained in white and yellow lights and the lowest was in green and blue lights. The growth in red light was more than the growth in green and blue lights and less than the growth in white and yellow lights. Also, the effect of light color on the amounts of chlorophyll a, total carotenoids, phycocyanin and allophycocyanin was not significant. However, the total amount of total phycobilins in white and yellow lights was significantly lower than other lights. Contrary to expectation, the effect of red light on the content of the red pigment, phycoerythrin, was positive and caused the greatest increase, significantly. Comparison of the ratio of pigments also showed that, only the effect of light color on the ratio of Phycocyanin to allophycocyanin was significant, and the highest amount was also obtained in red light. Also the correlation between the growth and phycoerythrin/phycocyanin or phycoerythrin/allophycocyanin ratio was significantly positive, but the growth and phycocyanin/allophycocyanin ratio were negatively correlated.CONCLUSIONThe findings of the present work, clearly show that the gene orchestra regulating the growth changes of spirulina is more influenced by the phytochromic ratios rather than absolute amounts of pigments. This cyanobacterial phytochromic role is also comparable to phytochromic roles in the higher plants on the other hand, the significant increase in the total content of phycobilins in the red light, without sever decrease in the growth, and due to the antioxidant properties of phycobilins, may have practical value in optimizing the potential of spirulina as a medicinal-food supplement. It also seems that yellow light among visible lights is an important factor in maintaining the balance between phytochromic ratios and preventing disturbances leading to the reduction of spirulina growth.

کلیدواژه ها:

Allophycocyanin ، Blue-green algae ، Carotenoid ، Chlorophyll ، Microalgae ، Phycobilin ، Phycocyanin ، Phycoerythrin ، Red light ، Yellow light