Abstract: Haematococcus pluvialis is a major source of natural astaxanthin due to its ability to accumulate astaxanthin under stress conditions. In order to establish a technical system for the regulation of efficient synthesis of astaxanthin, this experiment analyzed the effect of exogenous melatonin(MLT) on the defense response of Haematococcus pluvialis under nitrogen deficiency combined with high light condition. The results showed that the induction of exogenous MLT significantly promoted the accumulation of astaxanthin under stress conditions, with the highest content reaching 32.37 mg/g, which was 2.25 times higher than that of the control group. In addition, exogenous MLT increased the levels of intracellular NO and mitogen-activated protein kinase (MAPK), and upregulated the expression levels of dxs and chy, which are the key enzyme genes for astaxanthin synthesis. This study showed that the efficient synthesis of astaxanthin in Haematococcus pluvialis induced by exogenous MLT under high light and nitrogen stress may be related to the increase of NO and MAPK and the expression of the enzyme genes dxs and chy.
