Photosystem II Photochemistry and Phycobiliprotein of the Red AlgaeKappaphycus alvareziiand Their Implications for Light Adaptation

Abstract

Photosystem II photochemistry and phycobiliprotein (PBP) genes of red algaeKappaphycus alvarezii, raw material ofκ-carrageenan used in food and pharmaceutical industries, were analyzed in this study. Minimum saturating irradiance (Ik) of this algal species was less than 115 μmol m−2 s−1. Its actual PSII efficiency (yield II) increased when light intensity enhanced and decreased when light intensity reached 200 μmol m−2 s−1. Under dim light, yield II declined at first and then increased on the fourth day. Under high light, yield II retained a stable value. These results indicate thatK. alvareziiis a low-light-adapted species but possesses regulative mechanisms in response to both excessive and deficient light. Based on the PBP gene sequences,K. alvarezii, together with other red algae, assembled faster and showed a closer relationship with LL-Prochlorococcuscompared to HL-Prochlorococcus. Many amino acid loci in PBP sequences ofK. alvareziiwere conserved with those of LL-Prochlorococcus. However, loci conserved with HL-Prochlorococcusbut divergent with LL-Prochlorococcuswere also found. The diversities of PE and PC are proposed to have played some roles during the algal evolution and divergence of light adaption.