## 4 Conclusions  
Addition of 2-8 uM _rac_-GR24 improved the cell number density of _H. pluvialis_ during 30-d photosynthetic cultivation. The improvement in cell growth was mainly attributed to an enhanced physiological germination rate and higher chlorophyll \(a\) and \(b\) concentrations. After 30-d of cultivation, astaxanthin and total fatty acid contents of the _rac_-GR24-treated cells were lower or comparable to those of the untreated controls at the doses evaluated. Nevertheless, at the highest dose of 8 uM _rac_-GR24, thanks to the increased cell number density, both astaxanthin and total fatty acid production significantly improved to 26.1 mg/L and 361.6 mg/L, respectively, which were 21% and 60% higher than those of the controls. The proportion of polyunsaturated fatty acids among the total fatty acids was high (41.5-44.6%) in the _rac_-GR24-treated cells. These results indicate that _rac_-GR24 can promote both astaxanthin and PUFA production in photosynthetic _H. pluvialis_ cultures.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{6}{c}{**Fatty Acid Composition (\%)**} \\ \hline _rac_-**GR24 Concentration (uM)** & **0** & **2** & **4** & **6** & **8** \\ \hline Myristate & (C14:0) & 0.2 \(\pm\) 0.1 & 0.3 \(\pm\) 0.0 & 0.4 \(\pm\) 0.0 & 0.4 \(\pm\) 0.0 & 0.3 \(\pm\) 0.0 \\ Palmitate & (C16:0) & 35.2 \(\pm\) 2.0 & 31.7 \(\pm\) 1.3 & 30.5 \(\pm\) 0.8 & 27.6 \(\pm\) 1.2 & 27.2 \(\pm\) 1.0 \\ Palmitateate & (C16:1) & 0.1 \(\pm\) 0.2 & 0.3 \(\pm\) 0.2 & 0.5 \(\pm\) 0.0 & 0.5 \(\pm\) 0.0 & 0.5 \(\pm\) 0.0 \\ Oleate & (C18:1n9c) & 19.1 \(\pm\) 1.1 & 18.2 \(\pm\) 0.8 & 16.4 \(\pm\) 0.6 & 16.1 \(\pm\) 0.3 & 17.3 \(\pm\) 0.1 \\ Linoleate & (C18:2n6c) & 34.7 \(\pm\) 1.1 & 33.0 \(\pm\) 0.1 & 34.7 \(\pm\) 0.3 & 34.3 \(\pm\) 1.2 & 34.1 \(\pm\) 0.4 \\ \(\gamma\)-Linolenate & (C18:3n2c) & 0.5 \(\pm\) 0.7 & 1.6 \(\pm\) 0.1 & 1.7 \(\pm\) 0.0 & 1.81 \(\pm\) 0.0 & 1.9 \(\pm\) 0.0 \\ Linolenate & (C18:3n3c) & 5.1 \(\pm\) 0.5 & 6.9 \(\pm\) 0.2 & 7.0 \(\pm\) 0.5 & 7.7 \(\pm\) 0.3 & 8.6 \(\pm\) 0.4 \\ Others & & 5.0 \(\pm\) 1.8 & 8.0 \(\pm\) 1.6 & 8.8 \(\pm\) 1.1 & 11.7 \(\pm\) 3.0 & 10.1 \(\pm\) 1.0 \\ \hline \multicolumn{6}{c}{Saturated fatty acids} \\ \multicolumn{6}{c}{Monousaturated fatty acids} \\ \multicolumn{6}{c}{Polusunsaturated fatty acids (PUFAs)} \\ \multicolumn{6}{c}{Others} \\ \hline Total & 100 & 100 & 100 & 100 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Fatty acid composition of _Haematococcus phuvialis_ after 30 d cultivation under different _rac_-GR24 concentrations (2.0–8.0 uM).  
**Author Contributions:** Conceptualization, Y.-K.O., N.L. and R.M.; Methodology, R.M. and L.P.S.V.; Resources, N.L. and B.K.; Data Curation, R.M. and B.K.; Writing--Original Draft Preparation, R.M.; Writing--Review & Editing, Y.-K.O. and R.M.; Visualization, R.M., S.K. and D.P.A.I.; Supervision, N.L., B.K. and Y.-K.O.; Funding Acquisition, Y.-K.O. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was financially supported by the National Research Foundation of Korea [grant number NRF-2019R1A2C100346313] funded by the Ministry of Science and ICT, the Research/Development Program of the Korea Institute of Energy Research [KIERC0-2424], and the 2020 Post-Doc. Development Program of Pusan National University.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.