Abstract:

Because destruction of the ozone layer is becoming increasingly more serious, the amount of ultraviolet radiation reaching the earth's surface, esp. UV-B radiation that is harmful to the DNA of organisms, has increased. The increase in UV-B radiation has altered ecological systems on the earth and has emerged as one of the most noticeable forces of global change. Interest on the potential dangers and injuries from enhanced UV radiation on marine organisms (esp. marine plankton) has increased. A lot of work has been done on UV-B radiation effects on marine microalgae at the molecular, cellular, physiological and biochemical levels; however, there are few reports on red-tide microalgae. In this study, the effects of UV-B radiation on the protein and nucleic acid synthesis of three red-tide microalgae species, Heterosigma akashiwo, Alexandrium tamarense and Skeletonema costatum, were investigated to better understand the influence of UV-B radiation on marine ecological systems and the mechanism and occurrence of red tides. The microalgae were cultured in Erlenmeyer flasks with f/2 medium. Salinity of the seawater was (30.0±1.0) ‰ and the initial pH of the culture was ( 8.0 ±0.1). Cultures were grown at (19±1) ℃ under a 12 h∶12 h dark-light cycle at an illumination intensity of 3 000 Lx. Ultraviolet B radiation was provided by two UV-B tubes (Philips TL 40 w/12 uv) covered by a film of cellulose acetate (0.12 mm) to remove all radiation below 280 nm. In order to minimize the change of the filter properties of the film, the cellulose acetate was pre-burned for 48 h at a distance of 1 m from two UV-B lamps. Algae were exposed to UV-B radiation treatments of 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0 J·m -2, respectively, for 4 days. All experiments were carried out in triplicate. The responses of protein and nucleic acid synthesis in H. akashiwo, A. tamarense and S. costatum to UV-B radiation were studied using isotope-tracing methods. The results showed that the order of sensitivity from high to low in three red-tide microalgae to UV-B radiation was H. akashiwo, A. tamarense and S. costatum. The growth and DNA synthesis of H. akashiwo were inhibited. Whereas lower doses of UV-B radiation stimulated the growth and DNA synthesis of A. tamarense and S. costatum, higher doses had an inhibitory effect. The RNA and protein synthesis in all three species decreased with increased levels of UV-B radiation, but decreases in H. akashiwo were greater than in A. tamarense and S. costatum. Therefore, the sensitivity of RNA and protein synthesis to UV-B radiation enhancement in H. akashiwo was higher than that in A. tamarense and S. costatum.

Key words: Marine red-tide microalgae, Protein, Nucleic acid, Synthesis, Ultraviolet B radiation