Impacts Of Solar Radiation And Desiccation On The Physiology Of Aquatic-living Colonies Of Nostoc Flagelliforme

Nostoc flagelliforme Bomet & Flahault, named polularly as 'Facai' in Chinese, is aterrestrial cyanobacterium of great economic value. Althoug aquatic-living colonies weredeveloped under indoor conditions, little is know whether they can and how they would adapt tosolar radiation. Therefore, we exposed the colonies to different solar radiation treatments with orwithout UVR. Changes of their growth, effective quantum efficiency (â–³F/F_m') and pigmentswere estimated during the experimental period.High levels of both photosynthetically active radiation (PAR, 395-700 nm) and ultravioletradiation (UVR, 280-395 nm) reduced theâ–³F/F_m' of the colonies. Desiccation mought protectcolonies against high levels of both PAR and UVR, when aquatic-living colonies were exposedto short-term solar radiation treatment at noon. On the first day of long-term solar radiationtreatment,â–³F/F_m' was reduced about 54% by PAR and further declined 13% by UVR at noon.However,â–³F/F_m' recovered in the late afternoon. After two days' acclimation to solar radiation,the biomass of the colonies increased during the following days. UV-absorbing compounds,seytonemin and mycosporine-like amino acids (MAAs), increased by 124 and 9 times,respectively, in 9 days. Such increased UV-absorbing substances played an important role inprotecting the aquatic-living colonies of Nostoc flagelliforme from solar UVR. More studies willbe necessary to understand other mechanisms that protect aquatic-living colonies of Nostocflagelliforme from solar radiation, and how other stresses affect colonies.