Ultrastructural study on the process of astaxanthin accumulation in Haematococcus pluvialis Flotow under stress condition

The process of accumulation of astaxanthin in Haematococcus pluvialis Flotow under stress condition was studied by transmission electron microscopy. After three days of high lightexposure and nitrogen starvation, the pigment globules began to deposit quickly in the perinuclear cytoplasm of motile cell. After five days, the cytoplasm of motile cells was practically full of astaxanthin deposits. The most of motile cells loosed motile ability and transformed to akinetes with thick wall after seven days. Initially, the pigment deposits were spheroidal and small in sige. Afterward, the pigment globule guickly increased in number and dimension, and changed to irregular shapes by fusing each other. When motile cells transform to akinetes, the osmiophil character and location of the pigment deposits maintain identical. During astaxanthin accumulation, the starch grains also increased, which localiged in the parietal chloroplast, but the structure of chloroplasts remained intact through this process. It is indicated that environmental or nutritional stresses would induce the accumulation of astaxanthin, and the deposit would be extraplastidal localigation. It is also indicated that the vegetative cells would accumulate astaxanthin guickly.