| Natural auxin indole acetic acid (IAA), synthetic auxin naphthalene acetic acid (NAA) and 2,4-dichlorophenoxy acetic acid (2,4-D) were added into a nitrogen deficient culture medium to study the effects of different auxin dosage on growth characteristics, lipid accumulation and algal oil fatty acid composition of Chlorella vulgaris. The results showed that the optimal dosages of auxins were IAA 1.0 mg/L, NAA 2.5 mg/L and 2,4-D 1.0 mg/L. Under the optimal dosage of auxins, the highest biomasses of Chlorella vulgaris were 158, 159 mg/L and 164 mg/L respectively, which were 1.27, 1.28 times and 1.32 times of the deficiency nitrogen (ND)cultivation, and there was no significant difference in the biomass under normal culture (BG11) for 8 d in the whole cultural period. Auxin effectively offsetted the negative effect of nitrogen stress on biomass. The maximum total lipid content of Chlorella vulgaris with 1.0 mg/L IAA, 2.5 mg/L NAA and 1.0 mg/L 2,4-D groups were 1.72, 1.64 times and 1.74 times of that in BG11 group, respectively. The maximum total lipid yields were 61.38, 58.83, 64.22 mg/L, respectively, which were 1.49, 1.43,1.56 times of those in BG11 group. The maximum triglyceride contents were 27.97%, 25.66% and 33.21%, and the maximum triglyceride yields were 44.19, 40.80, 54.46 mg/L, respectively, which were significantly higher than those in BG11 group. The proportion of C16-C20 fatty acids in total fatty acids were 7199%, 73.75% and 84.81% respectively. The research showed that the three auxins had a significant positive effect in algal growth and lipid synthesis of Chlorella vulgaris, and the 2,4-D was the best. |
