Response of prostaglandin content in the red alga Gracilaria verrucosa to season and solar irradiance.

The influence of solar irradiance and seasons on prostaglandin (PG) and arachidonic acid (AA) content in the marine red alga Gracilaria verrucosa (Huds.) Papenf. (unattached form) was investigated. PGA(2), PGE(2), PGF(2), and 15-keto-PGE(2) were isolated from the alga, quantitatively analyzed as 4-methyl-7-methoxycoumarin esters by high-performance liquid chromatography, and their chemical structures were confirmed by 1H NMR. In June-September, the PG content in the alga was relatively stable (420 microg/g of dry wt. of PGE(2)+PGF(2); 40 microg/g of PGA(2)) and it increased 1.5 times in October. The highest level of PGs was detected in November (2500 microg/g of PGE(2)+PGF(2); 74 microg/g of PGA(2)) when water temperature was fairly low (5-10 degrees C). Algae grown for five months at 50% of incident photosynthetic active radiation (PAR(0)) contained two times less PGE(2) and PGF(2) than algae grown under natural conditions, but the amount of these PG in algae grown at 5% of PAR(0) was close to the normal level. On the contrary, when algae were grown at 5% of PAR(0) the content of PGA(2) increased up to 4 times compared to algae cultivated at 100% PAR(0). In June-November, the amount of AA in total algal lipids slightly varied from 48.9 to 56.7% and did not virtually depend on the light intensity. The probable reasons of the PG content variation in response to environmental factors are discussed.