Study on the photosynthetic characteristics of a Pyropia haitanensis red mutant cultured under different light intensities

Abstract

The photosynthetic characteristics of a Pyropia haitanensis red mutant mutated from a wild-type strain using chemical mutagens were studied. The aim was to compare the differences in photosynthetic characteristics between the red mutant and the wild type, and then to analyse the possibility of the red mutant as breeding material. The results indicated that the cytoplasm thickness of the red mutant and the wild type were similar, whereas the cell wall of the red mutant was significantly thinner than that of the wild type. Additionally, the chlorophyll a extract absorption spectra of both strains exhibited no obvious difference, whereas the absorption peaks at 498, 545, and 565 nm (which belong to phycoerythrin, PE) in the phycobiliprotein extract absorption spectra of the red mutant were clearly higher than those of the wild type. The PE content per area of the red mutant thallus was significantly higher than that of the wild type, and the ratios of PE to phycocyanin (PC) and PE to chlorophyll a were significantly higher in the red mutant than in the wild type. The net photosynthetic oxygen evolution rates of the red mutant and wild type cultured under different light intensities demonstrated that the oxygen evolution rates of all samples decreased with increasing light intensities, whereas the oxygen evolution rate of the red mutant was higher than that of the wild type under the same light intensities. The light response curves also indicated that the light-saturated photosynthetic rates (P _max), light saturation points (LSPs), and light compensation points (LCPs) of both strains decreased to different degrees with increasing light intensities and that the P _max and LSP values of the red mutant were significantly higher than those of the wild type under identical light intensities. In contrast, there were no obvious differences in the respiration rate (R _d) and in the LCP. The F _v/F _m values of both strains were similar before light treatment, whereas the F _v/F _m of the red mutants after culture under different light intensities (120 and 200 μmol photons m⁻² s⁻¹) for 3 days were significantly higher than those values of the wild type. Moreover, ∆F/F _m′ also exhibited a similar variation. Based on these results, the high content of PE in the P. haitanensis red mutant causes a steady red phenotype, and the increase in the PE concentration and the decrease in the thickness of the thallus may enhance its photosynthetic physiological activity. Thus, the red mutant of P. haitanensis may provide good material for Pyropia breeding.