BIOCHEMICAL AND PHYSIOLOGICAL-RESPONSES OF GRACILARIA-TENUISTIPITATA UNDER 2 DIFFERENT NITROGEN TREATMENTS

The influence of nitrogen on ribulose-1,5-bisphosphate carboxylase/oxy genase (Rubisco, EC 4.1.1.39) content is poorly understood in macroalg ae. N-deficient Gracilaria tenuistipitata Zhang et Xia var. liui was c ultivated in the laboratory under constant light intensity and tempera ture. Biochemical and physiological variables were monitored after a h igh (1 mM) or low (0.1 mM) nitrate pulse. Rubisco content in crude ext racts was estimated by SDS-PAGE with the Coomassie Blue staining proce dure. Nitrate was consumed immediately in the low-N treatment, but the re was always an external nitrate source in the high-N treatment. Tota l soluble proteins and phycobiliproteins decreased as internal nitroge n diminished in the low-N treatment, but kept fairly constant in N-suf ficient conditions. However, Rubisco content increased until the 7th d ay and then started to decrease in both cases. Fresh weight increment showed a better correlation with Rubisco than with pigment content.