134
7.1 General Overview of the Photosynthetic Processes
in Seagrass
The successful colonization of seagrass, the only group of marine angiosperms,
likely reflects their ability to cope with environmental fluctuations in the marine
systems. Photosynthesis is the main target of physiological regulation in that it
plays the central role in energy metabolisms that determine production and growth
of plants. Although angiosperms share essentially the same physiology
and biochemistry, seagrass exhibits adaptations to marine life which affect their
photosynthetic activity.
7.1.1 Light-Harvesting and Light Reactions
Photosynthetic reactions begin with the absorption of light energy followed by
electron transport within the thylakoid membrane, ATP synthesis and production of
reducing equivalent (NADPH) to be further used to assimilate CO 2 (Taiz et al.
2015). At least five major protein complexes, located in the inner thylakoid membrane, are involved in these processes: photosystem II (PSII), cytochrome b6f
complex, photosystem I (PSI), ATP synthase, and ferredoxin-NADP
+
-oxidoreductase complex. Both photosystems (PSII and PSI) form supercomplexes with
light- harvesting complexes LHCII and LHCI, respectively. These light-harvesting
complexes contain antenna molecules (chlorophyll a/b and carotenoids) and
binding proteins working in concert to harvest light energy. Several proteins associated with PSII and PSI supercomplexes have been identified and characterized
(Wicke et al. 2011).
Aquatic environment dramatically affects light quantity and quality. While the
intensity of light is reduced with depths, wavelength composition of downwelling
light is also altered as red, and far-red wavelengths are largely attenuated by the
water column, whereas blue light is highly scattered in the coastal water (Zimmerman
2003; Ragni and Ribera d’Alcala 2004). It is, thus, expected that light-harvesting
and the photosynthetic machinery of seagrasses are adjusted according to such light
attenuation. It appears that seagrasses have similar regions of maximum absorption
(blue 400–500 nm and red 600–700 nm; Drake et al. 2003; Mvungi et al. 2012) and
7.3 Knowledge Gaps .............................................................................................................. 146
7.3.1 The Function of Photoreceptors ........................................................................... 147
7.3.2 Mechanistic Understanding of Photosynthetic Carbon Fixation ......................... 147
7.3.3 Linkage Between Photosynthesis and Other Metabolic Pathways ...................... 148
7.4 Further Prospects for Integrating Seagrass Photophysiology
with Systems Biology ...................................................................................................... 151
7.5 Conclusion ....................................................................................................................... 153
References ................................................................................................................................. 154
P. Buapet
7.1 General Overview of the Photosynthetic Processes
in Seagrass
The successful colonization of seagrass, the only group of marine angiosperms,
likely reflects their ability to cope with environmental fluctuations in the marine
systems. Photosynthesis is the main target of physiological regulation in that it
plays the central role in energy metabolisms that determine production and growth
of plants. Although angiosperms share essentially the same physiology
and biochemistry, seagrass exhibits adaptations to marine life which affect their
photosynthetic activity.
7.1.1 Light-Harvesting and Light Reactions
Photosynthetic reactions begin with the absorption of light energy followed by
electron transport within the thylakoid membrane, ATP synthesis and production of
reducing equivalent (NADPH) to be further used to assimilate CO 2 (Taiz et al.
2015). At least five major protein complexes, located in the inner thylakoid membrane, are involved in these processes: photosystem II (PSII), cytochrome b6f
complex, photosystem I (PSI), ATP synthase, and ferredoxin-NADP
+
-oxidoreductase complex. Both photosystems (PSII and PSI) form supercomplexes with
light- harvesting complexes LHCII and LHCI, respectively. These light-harvesting
complexes contain antenna molecules (chlorophyll a/b and carotenoids) and
binding proteins working in concert to harvest light energy. Several proteins associated with PSII and PSI supercomplexes have been identified and characterized
(Wicke et al. 2011).
Aquatic environment dramatically affects light quantity and quality. While the
intensity of light is reduced with depths, wavelength composition of downwelling
light is also altered as red, and far-red wavelengths are largely attenuated by the
water column, whereas blue light is highly scattered in the coastal water (Zimmerman
2003; Ragni and Ribera d’Alcala 2004). It is, thus, expected that light-harvesting
and the photosynthetic machinery of seagrasses are adjusted according to such light
attenuation. It appears that seagrasses have similar regions of maximum absorption
(blue 400–500 nm and red 600–700 nm; Drake et al. 2003; Mvungi et al. 2012) and
7.3 Knowledge Gaps .............................................................................................................. 146
7.3.1 The Function of Photoreceptors ........................................................................... 147
7.3.2 Mechanistic Understanding of Photosynthetic Carbon Fixation ......................... 147
7.3.3 Linkage Between Photosynthesis and Other Metabolic Pathways ...................... 148
7.4 Further Prospects for Integrating Seagrass Photophysiology
with Systems Biology ...................................................................................................... 151
7.5 Conclusion ....................................................................................................................... 153
References ................................................................................................................................. 154
P. Buapet