PHOTOSYNTHETIC RESPONSE OF P-DEFICIENT GRACILARIA-TENUISTIPITATA UNDER 2 DIFFERENT PHOSPHATE TREATMENTS

Phosphorus-deficient Gracilaria tenuistipitata Zhang et Xia was cultur ed for 15 days at two different inorganic phosphate (P-i) concentratio ns: 3 mu M (low P-i treatment) or 30 mu M phosphate (high P-i treatmen t). The amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rub isco), phycobiliproteins, Chl a and total soluble proteins were higher in the high P-i than in the low P-i treatment. The total N content of the low P-i plants was lower than in plants grown at high P-i concent rations whereas the amount of total C was highest in low P-i plants. T he increase of Rubisco content in the high P-i treatment (3-fold) was parallel to the enhancement of the maximum photosynthetic rate which i ncreased 5-fold. This correspondence was also found in the low P-i tre atment in which Rubisco content and maximum photosynthesis did not cha nge significantly from the initial values. The photosynthetic efficien cy was also higher at high than at low P-i. The high P-i plants also s howed higher dark respiration and growth rates. The data presented her e suggest that marine macroalgae submitted to P-i deficiency exhibit a decrease in growth caused not only by P-i implication on energy trans fer in photosynthesis and respiration, but also by the diminution of t he amount of photosynthetic pigments and Rubisco.