74
S. Kato and T. Shinomura
basis in the cell and thylakoid fraction, respectively, compared with the cells grown
under illumination at 10–15 μmol photon m
−2 s
−1 (Lepetit et al. 2010). In a diatom
Phaeodactylum tricornutum, although diatoxanthin formation was not the only factor
to control NPQ, kinetics of NPQ was shown to be closely correlated with diatoxanthin concentration in the alga (Lavaud et al. 2002; Ruban et al. 2004). In E. gracilis
cells, we found that the molar ratio of cellular diatoxanthin content to diadinoxanthin content (Dtx/Ddx ratio) increased from 0.05 (55 μmol photon m
−2 s
−1 ) to
0.09 after the irradiation of intense light (920 μmol photon m
−2 s
−1 ), suggesting
that diatoxanthin might participate in photoprotection of E. gracilis during the longterm acclimation to intense light condition (Kato et al. 2017). On the other hand,
in C. meneghiniana, the majority of diadinoxanthin cycle pigments localized in the
peripheral antenna FCP (in particular FCPa) complexes and that the largest part
of high-light-induced newly synthesized diadinoxanthin cycle pigments might not
be protein bound and did not participate in the NPQ of C. meneghiniana (Lepetit
et al. 2010). Furthermore, Lepetit et al. (2010) suggested that those light-induced
additional pigments were dissolved in a monogalactosyldiacylglycerol lipid shield
around FCP complexes, serving an antioxidant function in the thylakoid membrane.
4.4.2 Light-Induced Expression of Carotenoid Biosynthetic
Gene
Light-induced expression of carotenoid biosynthetic genes was reported in several
microalgae. Steinbrenner and Linden (2001) reported increases in the expression of
phytoene synthase gene (psy) and carotenoid hydroxylase gene (chy) of H. pluvialis
cells after continuous illumination at 125 μmol photon m
−2 s
−1 for 12 h. Steinbrenner and Linden (2003) also observed a strong induction of the expression of psy,
phytoene desaturase gene (pds), lycopene β cyclase gene (lyc), and chy of H. pluvialis
grown under illumination at 50 μmol photon m
−2 s
−1 for 24 h, compared with those
in the cells illuminated at 10 μmol photon m
−2 s
−1 . Irradiation at 120 μmol photon
m
−2 s
−1 induced the expression of pds in C. zofingiensis (Huang et al. 2008). In P.
tricornutum, the expression of 1-deoxy-D-xylulose 5-phosphate synthase gene (dxs)
and psy was elevated during several hours after the dark-light transition (Eilers et al.
2016). In E. gracilis, our previous study revealed that continuous illumination at
920 μmol photon m
−2 s
−1 induced a 1.3-fold increase in the expression of phytoene
synthase gene (crtB) relative to the cells illuminated at 55 μmol photon m
−2 s
−1 ,
indicating that the carotenoid synthetic pathway of this alga responded to the intense
light at the transcriptional level (Kato et al. 2016) (Fig. 4.1a).
Bohne and Linden (2002) reported that, in the dark-light transition, blue light
induced the gene expression of psy and pds of Chlamydomonas reinhardtii to a
comparable level to those in cells irradiated with white light, whereas red light had
no obvious effect on the expression level of those genes. On the contrary, Steinbrenner
and Linden (2003) reported that blue and red light similarly induced the expression
S. Kato and T. Shinomura
basis in the cell and thylakoid fraction, respectively, compared with the cells grown
under illumination at 10–15 μmol photon m
−2 s
−1 (Lepetit et al. 2010). In a diatom
Phaeodactylum tricornutum, although diatoxanthin formation was not the only factor
to control NPQ, kinetics of NPQ was shown to be closely correlated with diatoxanthin concentration in the alga (Lavaud et al. 2002; Ruban et al. 2004). In E. gracilis
cells, we found that the molar ratio of cellular diatoxanthin content to diadinoxanthin content (Dtx/Ddx ratio) increased from 0.05 (55 μmol photon m
−2 s
−1 ) to
0.09 after the irradiation of intense light (920 μmol photon m
−2 s
−1 ), suggesting
that diatoxanthin might participate in photoprotection of E. gracilis during the longterm acclimation to intense light condition (Kato et al. 2017). On the other hand,
in C. meneghiniana, the majority of diadinoxanthin cycle pigments localized in the
peripheral antenna FCP (in particular FCPa) complexes and that the largest part
of high-light-induced newly synthesized diadinoxanthin cycle pigments might not
be protein bound and did not participate in the NPQ of C. meneghiniana (Lepetit
et al. 2010). Furthermore, Lepetit et al. (2010) suggested that those light-induced
additional pigments were dissolved in a monogalactosyldiacylglycerol lipid shield
around FCP complexes, serving an antioxidant function in the thylakoid membrane.
4.4.2 Light-Induced Expression of Carotenoid Biosynthetic
Gene
Light-induced expression of carotenoid biosynthetic genes was reported in several
microalgae. Steinbrenner and Linden (2001) reported increases in the expression of
phytoene synthase gene (psy) and carotenoid hydroxylase gene (chy) of H. pluvialis
cells after continuous illumination at 125 μmol photon m
−2 s
−1 for 12 h. Steinbrenner and Linden (2003) also observed a strong induction of the expression of psy,
phytoene desaturase gene (pds), lycopene β cyclase gene (lyc), and chy of H. pluvialis
grown under illumination at 50 μmol photon m
−2 s
−1 for 24 h, compared with those
in the cells illuminated at 10 μmol photon m
−2 s
−1 . Irradiation at 120 μmol photon
m
−2 s
−1 induced the expression of pds in C. zofingiensis (Huang et al. 2008). In P.
tricornutum, the expression of 1-deoxy-D-xylulose 5-phosphate synthase gene (dxs)
and psy was elevated during several hours after the dark-light transition (Eilers et al.
2016). In E. gracilis, our previous study revealed that continuous illumination at
920 μmol photon m
−2 s
−1 induced a 1.3-fold increase in the expression of phytoene
synthase gene (crtB) relative to the cells illuminated at 55 μmol photon m
−2 s
−1 ,
indicating that the carotenoid synthetic pathway of this alga responded to the intense
light at the transcriptional level (Kato et al. 2016) (Fig. 4.1a).
Bohne and Linden (2002) reported that, in the dark-light transition, blue light
induced the gene expression of psy and pds of Chlamydomonas reinhardtii to a
comparable level to those in cells irradiated with white light, whereas red light had
no obvious effect on the expression level of those genes. On the contrary, Steinbrenner
and Linden (2003) reported that blue and red light similarly induced the expression