Effects of temperature on the photosynthetic performance in mature thalli of the red alga Gelidium amansii (Gelidiaceae)

Abstract

Gelidium amansii, a commercial marine red alga, yields agar of excellent quality, but thus far its cultivation has been unsuccessful. Effects of temperature, especially high temperature, on the photosynthetic performance of this alga are poorly understood. The responses of net O2 evolution and pigment content in mature thalli exposed to various temperatures of 14, 18, 22, 26, and 30 °C for 2 days were studied. Fast Chl-a fluorescence kinetics and RuBPCase activity of plants exposed to 30 °C for 6, 12, 24, and 48 h were also determined. The results showed that 14–26 °C favored the net O2 evolution of G. amansii, which ranged from 0.50 to 1.53 μmol O2∙g−1∙min−1. High temperature (30 °C) decreases the contents of Chl-a and carotenoids. Phycobiliproteins increased in the thalli treated for 12 h and longer at 30 °C, suggesting that phycobiliproteins might play an important role in alleviation of oxidative damage caused by high temperature. In addition, the carbon assimilation process, light harvesting pigments, PSII reaction centers, and PSII acceptor side of G. amansii were damaged under 30 °C at 12 h; however, the PSII acceptor side was relatively stable during the initial 24 h treatment. At 30 °C both PSII photochemistry and carbon assimilation were negatively affected and impacted the photosynthetic response of G. amansii. RuBPCase activity showed a stronger positive correlation with photosynthetic oxygen release than the photochemistry. The results of this study confirm that the optimal temperature for G. amansii photosynthesis is between 22 °C to 26 °C and high temperatures of 30 °C and above limit G. amansii growth in near-shore waters.