Changes in ultrastructure and responses of antioxidant systems of algae ( Dunaliella salina) during acclimation to enhanced ultraviolet-B radiation

Abstract

Because of depletion of the stratospheric ozone layer, levels of solar ultraviolet-B (UV-B) radiation (280–315 nm), which penetrates the water column to an ecologically-significant depth, are increasing. In order to assess changes in ultrastructure and responses of antioxidant systems of algae during acclimation to enhanced ultraviolet-B radiation, Dunaliella salina was treated with higher dose of UV-B radiation (13.2 kJ m −2 d −1 dose) in this study. As compared to the control panel (8.8 kJ m −2 d −1), the treatment D. salina had many changes in ultrastructures: (1) thylakoids became swelled, and some of them penetrated into the pyrenoid; (2) lipid globules accumulated; (3) the amounts of starch grains increased; (4) cristae of mitochondria disintegrated; (5) inclusions in vacuoles reduced; and (6) cisternae of Golgi dictyosomes became loose and swollen. Enhanced UV-B irradiation also induced different responses of the antioxidant systems in D. salina: (1) contents of TBARS (thiobarbituric acid reacting substance) and H 2O 2 increased significantly ( p < 0.05); (2) levels of MAAs (mycosporine-like amino acids) increased at the beginning and subsequently decreased, and finally they leveled off at lower values; (3) there were not apparent variations for carotenoid contents, and contents of chlorophyll a presented a trend of initial increase and ultimate decrease; (4) both ascorbate and glutathione contents increased significantly ( p < 0.05); and (5) for the enzyme activities, POD activities increased remarkably ( p < 0.05), and SOD activities declined apparently ( p < 0.05), and CAT activity in D. salina had slight variations ( p > 0.05). In addition, growth curve displayed that enhanced UV-B radiation prominently inhibited increase of cell concentration when compared with control panel ( p < 0.05). Our results indicated that enhanced UV-B radiation caused ultrastructural changes of D. salina and induced different responses of antioxidant systems in D. salina.