Studies On The Characteristics Of Chlorophyll Fluorescence Of Haematococcus Pluviakis Under Stress Conditions

Haematococcus pluvialis is a single cellular green alga that grows in fresh water. Under adverse environmental conditions, such as: nitrogen deficiency, salt stress, high light intensity and other stress conditions, cell division stops, cells loss flagella and begin to accumulate astaxanthin. The green mobile cells gradually converted to the red cysts, and the volume of the cells increased drastically, the cell walls became thicker and the gene expression of lipid biosynthesis increased. The life history of the alga has three stages: green motile cells; green non-motile cells; and red cysts. And astaxanthin content of red cyst cells is up to the 3.0%~4.0% of the cell dry weight. Pluvialis is considered to be the best natural sources for astaxanthin.There are a number of researches on Haematococcus pluvialis cell growth and the conditions inducing astaxanthin accumulation, but the changes of chlorophyll fluorescence in the Haematococcus pluvialis under the environment stress is rarely reported. Chlorophyll fluorescence is the convenient indicators and probes of photosynthesis. Compared with the traditional measurement method, it has the advantages of briefness, rapidness and accuracy. The information of the light energy utilization can be obtained through the analysis of different fluorescence parameters, which can accurately reflect the stress condition of algal cells. This research focused on the changes in photosynthetic property of Haematococcus pluvialis. when accumulation of astaxanthin was induced under different stress conditions.The main results include:(1)The PSII function was significantly affected under high light intensity conditions. The inhibitory effect on green mobile cells(GM) was the most significant, while the inhibition on green non-motile cells(GNM) was less than that of other cells. There were different responses of three types of cells of Haematococcus pluvialis under the high light stress: under high light stress, the photosynthetic activity of RC cells kept constant for a long time, whereas the photosynthetic activity of the GM cells decreased rapidly.(2) Our study showed that nitrogen deficiency led to a decrease of photosynthetic ability and the inhibition on the synthesis of Chl-a. The J point of relative variable fluorescence increased under nitrogen deficiency, showing that nitrogen deficiency led to the inhibition of electron transfer from QA- to QB, and led to the accumulation of QA-.The absorption flux per RC(ABS/RC),the dissipation flux per RC(DI0/RC) and the trapping flux per RC(TR0/RC) were increased under nitrogen deficiency treatment, while the electron transport flux per RC(ET0/RC) were decreased. It was also shown that the PSII function was significantly affected under nitrogen deficiency condition.(3) With the increase of the salt concentration, the Chl-a content of Haematococcus pluvialis were decreased. The PSII function was significantly affected under salt stress conditions. Values of the maximum quantum yields(Fv/Fm) were decreased under salt stress concentrations(0, 0.1, 0.4M Na Cl), but when 1.2M Na Cl was applied, the downward trend of Fv/Fm was very significant. The results showed that the salt stress increased the energy flux per active reaction center, so that Haematococcus pluvialis cells can adapt to the salt stress environment.(4) Diphenylamine(DPA) could block the synthesis of astaxanthin. Under different light intensities, the effects of DPA on Haematococcus pluvialis were different. In the 200 μmol m-2 s-1 light illumination conditions, DPA did no effect on the growth of Haematococcus pluvialis, but the cells died off under DPA treatment with 400 μmol m-2 s-1light illumination condition. The PSII function was significantly affected under high light stress with DPA treatment.In conclusion, environmental stress(nitrogen deficiency, high light intensity, salt stress and DPA treatment) have significant effects on the growth and photosynthetic physiology of Haematococcus pluvialis. But responses of Haematococcus pluvialis and antioxidant mechanism of astaxanthin need to be further investigated.