Effect of inorganic carbon supply on the photosynthetic physiology of Gracilaria tenuistipitata
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Gracilaria tenuistipitata Zhang et Xia was cultured for 15 d at low, normal and high inorganic carbon concentrations under constant light, temperature and nutrient conditons. Carbonic anhydrase (CA; EC 22.214.171.124.) activity, ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco; EC 126.96.36.199) content, pigment content and C/N ratio were measured, and also the photosynthesis and growth rates. Both Rubisco content and CA activity increased under conditions of low inorganic carbon (Ci) but decreased at high Ci with respect to the control. The amount of pigments declined considerably at high Ci and was slightly higher at low Ci. The maximum rate of photosynthesis and the photosynthetic efficiency increased in low Ci and the opposite was found at high Ci concentration. The effects of Ci concentration on maximum rate of photosynthesis and photosynthetic efficiency are discussed in relation to the variation in pigment and Rubisco contents and CA activity. The data indicate that Ci may be an important factor controlling the photosynthetic physiology of G. tenuistipitata with regard, not only to the enzymes of Ci metabolism, but also to the pigment content.
Key wordsCarbonic anhydrase Chlorophyll Gracilaria Inorganic carbon Ribulose-1,5-bisphosphate carboxylase/oxygenase Phycobiliprotein Photosynthesis
maximum apparent photosynthetic rate
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