Effect of exogenous salicylic acid and ultraviolet radiation on Ulva prolifera under different light conditions

Abstract

To study the combined effects of exogenous salicylic acid (SA) and ultraviolet radiation (UV) on marine green algae Ulva prolifera under high (160 Μmol·m-2·s-1) and low (70 Μmol·m-2·s-1) light intensities, the growth, chlorophyll fluorescence parameters, photosynthetic rate of oxygen, superoxide dismutase (SOD) activity, soluble polysaccharide and soluble protein contents were investigated after they grew with or without ultraviolet (UV, 3.2 W·m-2) radiation in the presence or absence of SA (10 Μg·mL-1) for three days. The treatments included control group (CK), SA, UV and UV+SA treatments. Results showed that under the low light intensity without UV condition, the relative growth rate was enhanced, Chl a and soluble protein contents were decreased by SA. Under the high light intensity without UV condition, the relative growth rate was decreased, Chl a content, respiratory rate, photosynthetic rate of oxygen, soluble polysaccharide and soluble protein contents were enhanced by SA. Under the high light intensity with UV condition, the relative growth rate, Chl a and soluble polysaccharide contents were enhanced by UV+SA. Additionally, under the low light intensity with UV condition, compared to UV treatment, the maximum photochemical efficiency (Fv/Fm) and soluble protein contents were respectively increased by 139.8% and 32.2% under the UV+SA treatment. In conclusion, SA reduced the inhibitory effects of U. prolifera induced by UV, and the effects were more significant under the high light intensity.