# Antioxidant Production in _Dunaliella_
## 4 Tuning Antioxidant Enzyme Activity in _Dunaliella_
### Combination of Abiotic Factors on Antioxidant Enzyme Activity  
Most research on antioxidant enzyme activity in _Dunaliella_ focuses on only one factor, with a few studies assessing the combined effect of two factors. The studies indicate that a combination of factors is more effective in producing enzymatic antioxidant responses in _Dunaliella_ compared to exposure to a single stressor [37; 103; 137]. Factors that can be combined to produce an antioxidant response include UV-B radiation + high salinity + nitrogen deficiency (enhanced CAT, SOD, POD activities).  
UV-B radiation combined with high salinity and nitrogen deficiency enhanced CAT, SOD, POD activity relative to the non-radiated cells grown under normal growth conditions [34]. The combined effect of UV-B irradiation and nitrogen starvation can produce oxidative stress, which was eliminated by enhanced SOD, APX, and GPX activities relative to untreated _D. salina_ cells, whilst GR activity did not significantly change. However, the combined effect on antioxidant enzyme activity was significantly lower relative to the effect of either UV-B radiation or nitrogen deprivation [37]. Therefore, the combination of UV-B irradiation and nitrogen deprivation may not be effective in enhancing antioxidant enzyme activity in _Dunaliella_. Salinity (2-3 M NaCl) associated with propyl gallate can enhance CAT and APX activity, whilst SOD activity was unaltered in _D. salina_ compared to unstressed cells [152] suggests that salinity associated with other chemical-induced stress may increase in antioxidant enzyme activity in _Dunaliella_. There is a need for further research into this are to develop a deeper understanding of the 'tuning parameters' for enhanced enzymatic activity. The effects of abiotic factors on antioxidant enzyme activity are summarised in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Optimum**} & \multicolumn{3}{c}{**Antiv oxidant**} \\ \multicolumn{1}{c}{**Stress**} & \multicolumn{1}{c}{**Strains**} & \multicolumn{1}{c}{**Light (\(\mu\)mol Photon m\({}^{-2}\) s\({}^{-1}\))**} & **Salinity** & **Temperature** & **Enzymatic** & **Response** & **References** \\ \hline \multirow{4}{*}{Salinity} & 0.05–3.00 M & _D. tertiolecta_ & 150 & & & No effect on SOD & \\  & NaCl & (UTEX999) & Continuous light & 0.1–0.5 & 26 & & and CAT, GTR & \\  & & & Continuous light & & & activities APX & (2-3 M) & \\  & & & & & & CAT activity & \\  & & & & & & decreases with & \\  & & & & & & salinity & \\  & 0.5–5.5 M & _D. salina_ & Light: dark cycle (12:12 h) & 1.5 & (25 \(\pm\) 2) & & (0.5–2 M) and & \\  & & & & cycle (12:12 h) & & & then decrease & \\  & & & & & & & AY decreases & \\  & & & & & & (0.5–2 M) and & \\  & & & & & & & then constant \\  & & & & & & & CAT and SOD & \\  & & & & & & activities increase & \\  & & & & & & at hypo saline & \\  & & & & & & condition in _D._ & \\  & & & & & & & _tertiolecta_ & \\  & & & & & & APX activity in _D._ & \\  & & & & & & _tertiolecta_ higher & \\  & & & & & & at hypo saline & \\  & & & & & & and lower at \\  & & & & & & hyper saline & \\  & & & & & & condition \\  & & & & & & GPX activity & \\  & & & & & & decreased in _D._ & \\  & & & & & & _tertiolecta_ at \\  & & & & & & higher saline \\  & & & & & & (>1.25 M) & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Antioxidant enzymatic response of _Dunaliella_ exposed to different abiotic exogenous stress.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Stress**} & \multirow{2}{*}{**Strains**} & \multicolumn{2}{c}{**Optimum**} & \multirow{2}{*}{**Salinity**} & \multirow{2}{*}{**Temperature**} & \multirow{2}{*}{**Antioxidant**} & \multirow{2}{*}{**Enzymatic**} & \multirow{2}{*}{**References**} \\