260
temperature. Iron (450 μM) was added in the culture medium to convert these less ROS
to more ROS (
1
O 2 and OH
•
), thereby facilitating lipid peroxidation, which prompt the
cells to synthesize fatty acids and astaxanthin to protect their lipid vesicles. After
18 days of photoautotrophic induction, the astaxanthin content of the cells dramatically
increased by 75% at 30°C and 133% at 36°C, compared to that of cells exposed to heat
stress alone. Saha et al. (2013) evaluated carotenoid production and differential
response of various isoforms of SOD in D. salina under different stress conditions. The
combination of nitrogen depletion coupled with high-light illumination (240 μmol
m
−2
s
−1
) resulted into maximum carotenoid production during which the activity of
Fe-SOD induced while that of Mn-SOD retained. The micronutrient Mn is one of the
important minerals in algal photosynthesis which helps in enhancing inorganic mineral
accumulation. This observation suggests essential requirement of Mn during growth of
D. salina in stress conditions. Differential response of SODs is also reported as a shortterm strategy of H. pluvialis to survive under oxidative stress conditions, and the organism adopt chronic molecular defence strategies by increasing carotenoid biosynthesis
as long-term survival strategy (Wang et al. 2011). Einali and Valizadeh (2015) studied
accumulation of β-carotene and response of cellular antioxidant scavengers in D.
salina grown under salt stress. About 10% increase in β-carotene content was observed
when cells were grown in 1 and 3 M NaCl. The H 2 O 2 content decreased in cells grown
at 1 M NaCl, whereas cells grown at 2 and 3 M NaCl had higher accumulation of H 2 O 2 .
The activity of SOD increased with the increase in the salt concentration; APX activity
was highest in cells grown in 2 M NaCl, while CAT activity decreased in all treatments.
The total ascorbate and malondialdehyde (MDA, a natural biomarker of lipid peroxidation) contents also increased concomitantly with salt concentration.
Addition of various ROS agents to the culture media has been considered as a
possible measure for improving carotenoid synthesis by microalgae. Ip and Chen
(2005) used H 2 O 2 and sodium hypochlorite (NaClO) to generate OH
•
and
1
O 2 and
studied carotenogenesis and astaxanthin production in heterotrophic culture of C.
zofingiensis cultivated in the dark. Addition of 0.1 mM H 2 O 2 enhanced secondary
carotenoid biosynthesis, including astaxanthin, which was probably due to the formation of OH
•
radicals through the iron-catalysed Fenton reaction (Kobayashi et al.
1993). On the other hand,
1
O 2 sharply reduced the secondary carotenoid content. Ma
and Chen (2001a, b) observed increase in the astaxanthin formation from 5.8 to
6.5 mg/g in the mixotrophic culture of Chlorococcum sp. exposed to 0.1 mM H 2 O 2
for 3 days.
1
O 2 generated using methylene blue reduced the biomass and astaxanthin
content. Even under heterotrophic conditions (Ma and Chen 2001a), addition of
0.1 mM H 2 O 2 enhanced astaxanthin formation suggesting that light is not an obligatory enhancer for carotenogenesis. This suggests that suitable types of nonphotochemical ROS generators could substitute light to stimulate the biosynthesis
of secondary carotenoids in dark. It is known that ROS regulate astaxanthin accumulation by direct activation of biosynthetic latent enzymes GST (Aniya and Anders
1992) and GR (Miller and Claiborne 1991) or by activating the expression of genes
coding for carotenogenesis enzymes (Bouvier et al. 1998).
K. Chokshi et al.
temperature. Iron (450 μM) was added in the culture medium to convert these less ROS
to more ROS (
1
O 2 and OH
•
), thereby facilitating lipid peroxidation, which prompt the
cells to synthesize fatty acids and astaxanthin to protect their lipid vesicles. After
18 days of photoautotrophic induction, the astaxanthin content of the cells dramatically
increased by 75% at 30°C and 133% at 36°C, compared to that of cells exposed to heat
stress alone. Saha et al. (2013) evaluated carotenoid production and differential
response of various isoforms of SOD in D. salina under different stress conditions. The
combination of nitrogen depletion coupled with high-light illumination (240 μmol
m
−2
s
−1
) resulted into maximum carotenoid production during which the activity of
Fe-SOD induced while that of Mn-SOD retained. The micronutrient Mn is one of the
important minerals in algal photosynthesis which helps in enhancing inorganic mineral
accumulation. This observation suggests essential requirement of Mn during growth of
D. salina in stress conditions. Differential response of SODs is also reported as a shortterm strategy of H. pluvialis to survive under oxidative stress conditions, and the organism adopt chronic molecular defence strategies by increasing carotenoid biosynthesis
as long-term survival strategy (Wang et al. 2011). Einali and Valizadeh (2015) studied
accumulation of β-carotene and response of cellular antioxidant scavengers in D.
salina grown under salt stress. About 10% increase in β-carotene content was observed
when cells were grown in 1 and 3 M NaCl. The H 2 O 2 content decreased in cells grown
at 1 M NaCl, whereas cells grown at 2 and 3 M NaCl had higher accumulation of H 2 O 2 .
The activity of SOD increased with the increase in the salt concentration; APX activity
was highest in cells grown in 2 M NaCl, while CAT activity decreased in all treatments.
The total ascorbate and malondialdehyde (MDA, a natural biomarker of lipid peroxidation) contents also increased concomitantly with salt concentration.
Addition of various ROS agents to the culture media has been considered as a
possible measure for improving carotenoid synthesis by microalgae. Ip and Chen
(2005) used H 2 O 2 and sodium hypochlorite (NaClO) to generate OH
•
and
1
O 2 and
studied carotenogenesis and astaxanthin production in heterotrophic culture of C.
zofingiensis cultivated in the dark. Addition of 0.1 mM H 2 O 2 enhanced secondary
carotenoid biosynthesis, including astaxanthin, which was probably due to the formation of OH
•
radicals through the iron-catalysed Fenton reaction (Kobayashi et al.
1993). On the other hand,
1
O 2 sharply reduced the secondary carotenoid content. Ma
and Chen (2001a, b) observed increase in the astaxanthin formation from 5.8 to
6.5 mg/g in the mixotrophic culture of Chlorococcum sp. exposed to 0.1 mM H 2 O 2
for 3 days.
1
O 2 generated using methylene blue reduced the biomass and astaxanthin
content. Even under heterotrophic conditions (Ma and Chen 2001a), addition of
0.1 mM H 2 O 2 enhanced astaxanthin formation suggesting that light is not an obligatory enhancer for carotenogenesis. This suggests that suitable types of nonphotochemical ROS generators could substitute light to stimulate the biosynthesis
of secondary carotenoids in dark. It is known that ROS regulate astaxanthin accumulation by direct activation of biosynthetic latent enzymes GST (Aniya and Anders
1992) and GR (Miller and Claiborne 1991) or by activating the expression of genes
coding for carotenogenesis enzymes (Bouvier et al. 1998).
K. Chokshi et al.