EFFECT OF INORGANIC CARBON SUPPLY ON THE PHOTOSYNTHETIC PHYSIOLOGY OF GRACILARIA-TENUISTIPITATA

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 4.2.1.1.) activity, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) 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 (C-i) but decreased at high C-i with respect to the control. The amount of pigments declined considerably at high C-i and was slightly higher at low C-i. The maximum rate of photosynthesis and the photosynthetic efficiency increased in low C-i and the opposite was found at high C-i concentration. The effects of C-i 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 C-i may be an important factor controlling the photosynthetic physiology of G. tenuistipitata with regard, not only to the enzymes of C-i metabolism, but also to the pigment content.