Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina
1996
Machalek, K.M. | Davison, I.R. | Falkowski, P.G.
Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 degrees C and irradiances of 15 and 150 micromol photons m-2 s-1. When measured at a standard temperature (17 degrees C), rates of light-saturated photosynthesis (Pmax) were higher in 5 degrees C-grown algae (c. 3.0 micromol O2 m-2 s-1) than in 17 degrees C-grown algae (c. 0.9 micromol O2 m-2 s-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 degrees C-grown algae than in algae grown at 17 degrees C. Light-limited photosynthesis responded similarly to high temperature and low light. Photon yields (alpha) were higher in algae grown at high temperature (regardless of light), and at 5 degrees C in low light, than in algae grown at 5 degrees C in high light. Differences in a were correlated with light absorption; both groups of 17 degrees C algae and 5 degrees C low-light algae absorbed c. 75% of incident light, whereas 5 degrees C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content, PSII reaction centre densities and the fucoxanthin-Chl a/c protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (phi max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m-2). We suggest that complex metabolic regulation allows L. saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.
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