| Paclobutrazol (PP333) and uniconazole are two active members of the triazole family, which are widely used as plant growth regulators. The effects on growth, lipid peroxidation and some antioxidant enzymes activities of four species of marine microalga, Platymonas helgolandica, Pavlova viridis, Pyramidomonas sp. and Nitzschia closterium, in response to different concentrations of PP333 and uniconazole were studied by using experimental ecology and biochemical methods. The results are as follows:1. Growth and Antioxidant Responses of Four Marine Microalgal Species to PP333.(1) Low concentrations (≤5 mg/L) of PP333 had no significant effects on growth of P. helgolandica. Higher concentrations (≥15 mg/L) of PP333 could inhibit the growth of P. helgolandica significantly, the inhibitory effects were observed in dry weight, chlorophyll-a, soluble carbohydrate and protein content. The superoxide dismutase (SOD) and peroxidase (POD) activities of P. helgolandica showed an increasing trend at low concentrations (≤1 mg/L) and decreasing trend at higher concentrations (≥5 mg/L) of PP333. However, catalase (CAT) activity was lower than control at different concentrations of PP333.(2) PP333 could promote the growth of P. viridis at low concetrations (≤5 mg/L), dry weight, chlorophyll-a, soluble carbohydrate and protein content were also increased (p < 0.05). While significant inhibition on growth of P. viridis was observed at higher concentrations (≥15 mg/L) of PP333. The effects of PP333 on antioxidant enzyme activities of P. viridis were the same as on P. helgolandica.(3) Promotion effects were observed on growth and antioxidant enzyme activities of Pyramidomonas sp. at low concentrations of PP333, the content of chlorophyll-a, soluble carbohydrate and protein were also higher than control (p < 0.05). However, PP333 could inhibit growth and three antioxidant enzyme activities of Pyramidomonas sp. at higher cocentrations (p < 0.05).(4) PP333 could decrease the growth and CAT activity of N. closterium in the present condition. Dry weight, chlorophyll-a and protein content of N. closterium were inhibited significantly (p < 0.05). Significant increase in soluble carbohydrate content and POD activity were observed at low concentrations of PP333, while significant decrease were measured at higher concentrations.(5) The 96h-EC50 values of PP333 againast P. helgolandica, P. viridis, Pyramidomonas sp. and N. closterium were 28.60,24.94,24.97 and 5.62 mg/L, respectively. So the sensitivities of four marine microalgae to PP333 were P. helgolandica < Pyramidomonas sp. < P. viridis < N. closterium2. Growth and Antioxidant Responses of Four Marine Microalgal Species to uniconazole.(1) Uniconazole caused no inhibition on the growth of P. helgolandica and P. viridis at low concentrations (≤6 mg/L), while at higher concentrations (≥9 mg/L), it showed significantly inhibitory effects on growth (p < 0.05). Uniconazole could inhibit dry weight, chlorophyll-a, soluble carbohydrate and protein content of P. helgolandica and P. viridis after 96 h at higher concentrations. Significant increase in MDA levels were observed both in P. helgolandica and P. viridis at higher concentrations (≥12 mg/L) of uniconazole with respect to control (p < 0.05). The SOD and POD activities of P. helgolandica and P. viridis showed an increasing trend at low concentrations and decreasing trend at higher concentrations of uniconazole.(2) Uniconazole significantly increased dry weight, chlorophyll-a and soluble carbohydrate content of Pyramidomonas sp. after 96 h at low concentrations. Significant inhibition on growth of Pyramidomonas sp. was observed at higher concentrations of uniconazole. Remarkable effects were also observed on the antioxidation of Pyramidomonas sp. at higher concentrations of uniconazole. Among these, a reduction in protein content, a decrease in SOD and CAT enzymatic levels and an increase in lipid peroxidation (detected through MDA levels). (3) Uniconazole could inhibit the growth, dry weight and chlorophyll-a content of N. closterium in the present condition. A significant increase was observed in soluble carbohydrate content of N. closterium after 96 h at low concentrations (≤6 mg/mL) of uniconazole (p < 0.05), while an obvious reduction in protein content was measured at higher uniconazole concentrations (≥12 mg/L). The effects of uniconazole on antioxidation of N. closterium were the same as Pyramidomonas sp..(4) The 96h-EC50 values of uniconazole againast P. helgolandica, P. viridis, Pyramidomonas sp. and N. closterium were 11.10,11.56,9.42 and 4.34 mg/L, respectively. So the sensitivities of four marine microalgae to uniconazaole were P. viridis < P. helgolandica < Pyramidomonas sp. < N. closterium.3. The present results demonstrated that the effects of PP333 and uniconazole on four marine microalgae were different from each other. PP333 and uniconazole show different activities to different marine microalgae.The research in this paper present enriched the research system of effects of plant growth regulators to microalgae, it also supplied some scientific information to the use of PP333 and uniconazole in the future.
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