探討兩種常用植物生長調節劑(Gibberellic acid, Paclobutrazol)對水生蚤類(Daphnia pulex)之影響

Purpose: The present study evaluated whether the plant growth regulators, gibberellic acid and paclobutrazol, would be embryotoxic to cladoceran Daphnia pulex (water fleas) in the laboratory. Methods: For this study, we developed an in vitro assay system to detect toxic compounds in the aquatic environment containing 5th generation water flea (cladoceran) eggs. The eggs were placed in a culture medium containing nature-imitating water (hard water). Then, two representative plant growth regulators, gibberellic acid and paclobutrazol, were added at various doses in a series of experiments in which we performed acute toxicity tests for EC50 values and evaluated embryo toxicity by observing the occurrence of visible morphological embryonic abnormalities. Results: We found gibberellic acid and paclobutrazol to be toxic to developing embryos. The threshold concentration of gibberellic acid for the occurrence of developmental abnormalities was 0.5 mg/L and paclobutrazol 0.2 mg/L. The developmental abnormalities consisted primarily of curved or unextended shell spines, underdeveloped first antennae, and underdeveloped Malpighian tubes. The greater the exposure to the chemicals, the greater the incidence of these abnormalities. Conclusion: Gibberellic acid and paclobutrazol are embryotoxic to daphnids and cause growth retardation, abnormalities and death.