Study On The Effects Of Phytohormones On The Accumulation Of Oil And DHA By Schizochytrium Under The Condition Of Nitrogen Limitation

Docosahexaenoic acid(DHA)is a polyunsaturated fatty acid of the omega-3series with the longest carbon chain found so far.It has important physiological functions such as promoting brain development in infants and young children,preventing and treating cardiovascular diseases,and improving retinal function.Schizochytrium has become one of the model strains for industrial production of DHA because of its rich oil and DHA and short growth cycle.At present,a variety of measures have been used to promote the production of oil and DHA in Schizochytrium so as to reduce the production cost of DHA.However,researches on using plant hormones and plant hormones coupled with nitrogen stress to increase the production of Schizochytrium oil and DHA are fresh see report.Therefore,this thesis intends to screen out the plant hormones that promote the production of Schizochytrium oil and DHA,and then use plant hormones coupled with nitrogen stress to further promote the production of Schizochytrium oil and DHA.It hopes to provide a new research idea for Schizochytrium to obtain higher yield of oil and DHA.The main research contents are as follows:1.The optimal concentrations of the six plant hormones to promote the production of oil and DHA in Schizochytrium are: Naphthalene acetic acid(NAA):0.04 mg/L;6-benzyl adenine(6-BA): 0.08 mg/L;Gibberellin(GA): 0.5 mg/L;2,4-Dichlorophenoxyacetic acid(2,4-D): 1.5 mg/L;Diethylaminoethanol hexanoate(DA-6): 0.05 mg /L;Methyl jasmonate(Me JA): 15 mg/L.Among them,the three plant hormones 2,4-D,DA-6,and Me JA promote the oil production and DHA production of Schizochytrium to a greater extent.The oil production is 17.69 g/L,19.06 g/L,and 18.19 g/L,respectively.Compared with the control group,the oil output increased by 74.24%,85.58%,77.11%,and the DHA output was 6.94 g/L,7.23 g/L,and 7.22 g/L,respectively.Compared with the control group,the DHA output increased respectively.61.39%,70.92%,70.68%.2.Schizochytrium promotes the production of oil and DHA under the limited conditions of nitrogen source when the concentration of sodium glutamate(MSG)is5 g/L,the optimal nitrogen stress(MSG-L)concentration is determined to be 5 g/L.Schizochytrium under optimal nitrogen stress(MSG-L)coupled with 2,4-D,DA-6,Me JA,respectively,compared with separate nitrogen stress conditions,its oil production and DHA production were significantly increased.And it was further determined that the optimal time for Schizochytrium to couple with plant hormones2,4-D,DA-6,and Me JA under nitrogen stress was 0 h,48 h,and 0 h,respectively.3.Nitrogen stress coupled with phytohormones induces the increase in the activity of antioxidant enzymes SOD and CAT in Schizochytrium cells,effectively alleviating the oxidative stress under nitrogen stress environment;promoting the synthesis of carotenoids in Schizochytrium cells;reducing Intracellular protein and polysaccharide content of Schizochytrium.This result indirectly explains why the coupling of plant hormones under nitrogen stress further promotes the accumulation of Schizochytrium oil and DHA.