THE TOXIC EFFECT OF STREPTOMYCIN ON THE GROWTH AND PHOTOSYNTHESIS OF NOSTOC USING THE CHLOROPHYLL FLUORESCENCE ANALYSIS

To explore the toxic effects of streptomycin, the growth and chlorophyll fluorescence were measured in Nostoc treated with different concentrations (0, 0.05, 0.10, 0.20, 0.50 and 1 mg/L) of streptomycin. The results indicated that the EC₅₀ of streptomycin to Nostoc (96h-EC₅₀) was (0.13±0.037) mg/L at the 96h. Streptomycin significantly decreased the content of chlorophyll a at all concentrations. In a concentration-dependent pattern, streptomycin significantly reduced the maximum photochemical efficiency (φP₀), variable fluorescence (F_v), potential activity of PSⅡ (F_v/F₀), active reaction center per unit area (RC/CS₀), the performance index based on absorbed light energy (PIabs) and the quantum energy yield of the light energy absorbed by the reaction center for electron transfer (φE₀). However, Streptomycin significantly increased the maximum fluorescence relative to chlorophyll a (F_m/Chl. a), the light energy absorbed by each active reaction center (ABS/RC) and heat dissipation (DI₀/RC) in a concentration-dependent pattern. A K-point at chlorophyll a fluorescence transient curve was found when the concentration is greater than 0.1 mg/L. These results suggest that streptomycin might affect the growth of Nostoc by inhibiting the electron transport of photosynthetic system Ⅱ (PSⅡ) and reducing active reaction centers, and that high concentrations of streptomycin showed an inhibitory effect on the growth of algae.