ACCUMULATION OF SELENIUM IN ULVA LAETEVIRENSARESCHOUG AND EFFECTS ON OXIDATIVE STRESS-RELATEDMETABOLISM AND ULTRASTRUCTURE

Selenium (Se) occurs in the aquatic environment principally under two oxidation states, Se(IV) selenite and Se(VI) selenate. Se accumulation in algae can be also affected by the presence of sulfur (S), which is a well-known antagonist of selenate in the form of sulfate. In the current study the impact of selenium (Se) on the green macroalga Ulva laetevirens Areschoug was investigated. The alga was provided for 10 days with concentrations of selenate (Na2SeO4) ranging within 0-100 μM. Se accumulation in the seaweed was linearly related to the given selenate concentration and, apparently, this relationship was not affected by the high sulfate concentration (~10 mM) recorded in the seawater used as the growth medium. Se increased the activity of oxidative stress-related enzymes (superoxide dismutase, SOD, and catalase, CAT), even when selenate was supplied to U. laetevirens at low concentration (2.5 μM). This indicates that the antioxidative defence system plays a pivotal role in overcoming selenium-derived oxidative stress-damages in the macroalga U. laetevirens. Also, selenate exposure did not cause morphological and ultrastructural alterations in U. laetevirens cells, and the function and ultrastructure of chloroplasts was unchanged compared to the control seaweeds.