Studies On Light Intensity Adaptability And High Light Stress Response Of Two Benthic Seaweeds

Red algae and green algae are both primary photosynthetic eukaryotes, they are the important object in the study of species origin, phylogeny and evolution. And the light environment has a great role in promoting the evolution of algae. In this paper,the light intensity adaptability and the mechanism of high light stress response of Betaphycus gelatinum and Caulerpa lentillifera were studied by chlorophyll fluorescence and transcriptome sequencing, which is helpful to understand the photosynthetic characteristics and adaptation mechanisms of these two primary photosynthetic eukaryotes at different light intensities. The results will help to explain the coupling relationship between algal evolution and light adaptation. At the same time, it is of a certain guiding significance to improve the economic value of these two algae and optimize their breeding technology.The effects of different light intensities on the chlorophyll fluorescence characteristics of B. gelatinum and C.lentillifera were analyzed,and it found that both species of benthic seaweed have low light adaptability. C. lentillifera was more sensitive to light intensity, the photosynthetic electron transport rate was significantly inhibited under the condition of 120 ?mol/(m2·s), but B. gelatinum could adapt to the light intensity of 120 ?mol/(m2·s) by the light energy regulatory mechanism. The electron transport activity of C. lentillifera was inhibited under the light intensity of 360 ?mol/(m2·s), and C. lentillifera would further reduce the use of light energy efficiency to improve the tolerance of light. B. gelatinum would reduce the use of light energy efficiency and enhance the activity of electron transport to improve the tolerance of light under the light intensity of 360 ?mol/(m2·s). But B. gelatinum and C.lentillifera would both suffer severe light damage when the samples were treated with the light intensity of 360 ?mol/(m2·s) for up to 12 h.The changes of related metabolic pathways under different light conditions indicated that the synthesis of chlorophyll a was down-regulated, and the light capture ability of antenna protein was reduced under high light of B. gelatinum and C.lentillifera. B. gelatinum would improve the synthesis of lycopene and ?-carotene in algae, the genes of glutathione reductase, glutathione S-transferase, ascorbate peroxidase, superoxide dismutase and catalase were all up-regulated to improve the antioxidant capacity of algae. And B. gelatinum would reduce light suppression by enhancing photorespiration. But C. lentillifera would reduce the light damage by the lutein cycle, and enhance the photosynthetic carbon fixation to consume excess ATP.The down-regulation of Mpv17 protein produced a certain inhibitory effect on the production of reactive oxygen species.