Effects of different LED light-qualities on growth,development and physiological characteristics of the unisexual thallus inPyropia haitanensis

In order to explore the optimum spectral components for growth and development of thallus of Pyropia haitanensis, the effects of different light qualities (white light, WL; blue light, BL; green light, GL; red light, RL) from light-emitting diode (LED) illuminations on the vegetative growth, developmental differentiation, maximal quantum efficiency of PSⅡ photochemistry and photosynthetic pigment contents of female thalli were studied. Results showed that the average length and fresh weight of thalli under WL after 25 days culturing were 2.42-3.86 and 2.64-4.50 times higher than those of thalli cultured in monochromatic light qualities, respectively. The growth rate of thalli was fastest when cultured in polychromatic WL, while it was limited in the monochromatic lights (BL, GL and RL). RL and GL were significantly adverse for the synthesis of phycobiliproteins. Compared to WL, the phycoerythrin contents of thalli under RL and GL decreased by 44.1% and 43.2%, respectively, and the phycocyanin contents of thalli decreased by 11.6% and 12.5%, respectively. However, the phycoerythrin and phycocyanin contents of thalli under BL were increased by 94.3% and 16.2%, respectively, compared with that under WL, and the highest F_v/F_m values kept on a continuous uptrend through the whole culturing period suggested that thallus had long-term acclimation to BL. It was noteworthy that both GL and BL accelerated cell differentiation and rapidly motivated the parthenogenetic development in the apical parts of thalli, while WL and RL never had such effects. The pathway of parthenogenetic spores developing into normal parthenogenetic conchocelis were promoted by BL, but blocked by GL. All of the parthenogenetic spore germlings in GL overflowed their cell inclusions and finally hollowed and demised. These results indicated that monochromatic lights limited the vegetative growth of thalli, and significantly affected the photosynthetic pigment components and the maximum photochemical efficiency (F_v/F_m) of PSⅡ, yet BL was favourable for parthenogenetic development of unisexual thalli. It also provided a reference for the further studies on the light adaptation mechanism of the thallus in P. haitanensis.