Effect Of Nitrogen Supply On Photosynthesis And Carbonic-Anhydrase Activity In The Green Seaweed Ulva-Rigida (Chlorophyta)

Abstract

Photosynthesis rate and carbonic anhydrase (CA) activity have been studied in the green seaweed Ulva rigida C. Agardh (Chlorophyta) grown in seawater (SW) and SW supplemented with 40 mu M NH4Cl (N-SW). Higher growth and maximal O-2 evolution rates were observed in N-SW- than in SW-grown seaweeds. Western blot analysis of the total homogenates probed with antibodies raised against small subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) showed crossreaction with a 15 kdalton polypeptide in both SW- and N-SW-grown plants, although the band was more intense in N-SW-grown plants. Carbonic anhydrase activities in the total homogenate and in the soluble protein fraction were higher in N-SW-grown plants. Although the pellets from both plants showed a considerable CA activity, the activity of CA in the thylakoid membranes was undetectable. The low nitrogen concentration is a major environmental factor that affects the level of RuBisCO and CA, and therefore CO2 assimilation in U. rigida.