Effects of ultraviolet-B radiation on the reproduction, germling growth, and physio-biochemical characteristics of green alga Ulva pertusa (Chlorophyta)

Jie Zhang, Hengjiang Cai, Siqi Hu, Wenjing Xie, Weiyao Zhao, Wenfei Gu, Zhu J, Zheng Li

Introduction Enhanced ultraviolet-B (UV-B, 280-320nm) radiation caused by ozone depletion is a global environmental issue. Ulva pertusa Kjellman (Chlorophyta) is often found in shallow intertidal environments exposed to ambient solar radiation. Therefore, the effects of UV-B radiation on the reproduction, germling growth, and physiological and biochemical characteristics of Ulva pertusa were investigated in this study. Methods Four daily UV-B doses (0.00, 0.31, 0.62 and 1.24 kJ/m 2 ·d) were applied to U. pertusa samples for 30 days. Results UV-B radiation reduced the density of adherent propagules (zoospores and gametes), in addition to the germination rate. It also reduced the length and leaf surface area of Ulva pertusa germlings, and this effect increased with UV-B radiation treatment dose. Additionally, UV-B radiation increased the mortality rate of germlings; the process of cell death in germlings involved a reduction in green pigment and cell contraction. Under high-dose UV-B radiation (1.24 kJ m⁻² d⁻¹), the chlorophyll a content of germlings decreased significantly, while the soluble protein content increased. UV-B-exposed germling cells produced excessive superoxide radical (•O₂⁻) and hydrogen peroxide (H₂O₂), leading to increased malondialdehyde content. However, superoxide dismutase and catalase activities in germlings were elevated for the removal of excessive reactive oxygen species. Discussion These findings demonstrate that UV-B radiation impairs the reproduction and early growth of Ulva pertusa through oxidative stress, and that the antioxidant defense system is insufficient to fully prevent UV-B-induced damage.