Studies On The Photosynthetic Charcateristics And Inorganic Carbon Utilization Mechanisms In Green Cells Of Haematococcus Pluvialis

Haematococcus pluvialis is a freshwater single cell green alga.The cell of H.pluvialis can accumulate astaxanthin under stress,which makes this species an ideal source for astaxanthin production.Although it has been widely reported in the literature that the species can be used to production as astaxanthin,little has been known about the mechanisms of ultilizing inorganic carbon source by green motile cells of the species.Using the strain H.pluvialis CG-11 as a model organism,we explored the effects of light intensity,temperature and pH on the photosynthesis and mechanisms of the inorganic carbon utilization and their possible affecting factors.The results were summarized as follows:1.The photosynthesis of H.pluvialis under different light intensities,temperatures and pH values was measured using photosynthetic oxygen evolution rate and chlorophyll fluorescence methods. The results showed that the light saturation point of Haematococcus pluvialis CG-11 was 129.25μmol·m^-2·s^-1,the suitable photosynthesis temperature 25-30℃,the pH values 7.5-8.0.2.The mechanism of inorganic carbon utilization in Haematococcus pluvialis CG-11 was explored through pH drift technique,photosynthetic oxygen evolution rate under different inhibitors, and optical microscopy observation.Cells of H.pluvialis CG-11 can use CO₂-concentrating mechanism function,contained no extracellular carbonic anhydrase,however,intracellular carbonic anhydrase was detected.Research on the HCO₃^- transport action suggested that Haematococcus pluvialis CG-11 had HCO₃^- transporter,which,however showed minimum contribution on photosynthetic requirement of inorganic carbon.Passing air-cultivation of H.pluvialis clearly demonstrated that the structure of pyrenoid were hexahedron,while,under high concentrations of CO₂,the structure of pyrenoid was not observated.This significant differenence in the presence of pyrenoid in algal cell indicated that the cell may have a CO₂-concentrating mechanism.3.The measurements of H.pluvialis CG-11 growth and carbonic anhydrase activity under different nutrilit and environmental conditions demonstrateed that H.pluvialis CG-11 grew best at 0.5%of carbon dioxide concentration,5 mmol·L^-1 sodium bicarbonate,and pH 8.0,while the carbonic anhydrase was most activity when cells were cultured with air flow,sodium bicarbonate less than 5 mmol·L^-1,and pH 9.0.In addition,it was observed that the activity of carbonic anhydrase and the cell growth of H.pluvialis CG-11 could be enhanced significantly when the ratio of nitrogen and phosphorus was 9/2 and zinc ion concentration 1μmol·L^-1.