150
an increase in the expression of photorespiratory genes, as well as proteins associated with photorespiration, has been observed when plants are subjected to energy
imbalance (Lepistö et al. 2009; Abogadallah 2011). Tobacco overexpressing chloroplastic glutamine synthetase (GS2) exhibits higher tolerance to strong light compared to those with a lower level of GS2 (Kozaki and Takeba 1996). Similarly,
enhanced cyclic electron flow around PSI, chlororespiration, and the Mehler reaction were observed in various plant species under mild stress conditions (Heber
2002; Makino et al. 2002; Rumeau et al. 2007; Huang et al. 2012). These alternative
electron flows coordinate in their protective roles, and the contribution of each process under certain stress condition differs among plant species (Heber 2002; Makino
et al. 2002; Rumeau et al. 2007).
7.3.3.2 Photosynthesis, Respiration, and Nitrogen Metabolisms
Photosynthesis and respiration are primary pathways of carbon and energy metabolism in plants. The balance between photosynthetic production and respiratory
breakdown of carbohydrates determines plant carbon gain and potentially growth.
These two processes are interrelated via an exchange of metabolites such as ATP,
reducing equivalents and other carbon-containing intermediates. Photosynthesis
and respiration respond to changes in environmental factors in a different manner
and thus result in an alteration of photosynthesis to cellular respiration ratio. The
effects of increased temperature and salinity on photosynthesis and respiration have
been investigated in seagrasses, and a clear shift in plant carbon metabolisms has
been observed (as discussed in the previous section). Cellular respiration in the
seagrass Z. marina is inhibited in the light, whereas the respiratory rates, as well as
expressions of respiratory genes, show diel variations (Rasmusson and Björk 2014;
Rasmusson 2015). Although it has been proposed that such variations could be a
result of an interplay between photosynthesis, photorespiration, and cellular respiration, the mechanisms involved are not completely understood. In terrestrial plants,
high CO 2 increases the respiratory breakdown of carbohydrates (Ainsworth et al.
2006; Li et al. 2013). Such an increase in respiratory activity was found in conjunction with an accumulation of carbohydrates as well as an increase in transcripts
associated with glycolysis, tricarboxylic acid cycle, and mitochondrial electron
transport (Rogers et al. 2004; Gillespie et al. 2012). The opposing utilization and
release of O 2 and CO 2 between photosynthesis, respiration, and photorespiration
make it challenging to assess the rates of these processes in the light using classical
gas exchange method. Additionally, lacunae present in all seagrasses and the potential internal recycling of both O 2 and CO 2 interfere with gas exchange measurement
and manipulations of available O 2 and CO 2 .
The interaction between carbon and nitrogen metabolisms in the context of
increasing CO 2 has been widely investigated in the terrestrial model plants (Yong
et al. 2000; Bloom et al. 2002; Cousins and Blooms 2004; Takatani et al. 2014).
Suppression of nitrate assimilation by a downregulation of nitrate and nitrite reductase activities was demonstrated in wheat exposed to elevated CO 2 (Bloom et al.
2002), whereas Arabidopsis mutant with low nitrate reductase activity exhibited
P. Buapet
an increase in the expression of photorespiratory genes, as well as proteins associated with photorespiration, has been observed when plants are subjected to energy
imbalance (Lepistö et al. 2009; Abogadallah 2011). Tobacco overexpressing chloroplastic glutamine synthetase (GS2) exhibits higher tolerance to strong light compared to those with a lower level of GS2 (Kozaki and Takeba 1996). Similarly,
enhanced cyclic electron flow around PSI, chlororespiration, and the Mehler reaction were observed in various plant species under mild stress conditions (Heber
2002; Makino et al. 2002; Rumeau et al. 2007; Huang et al. 2012). These alternative
electron flows coordinate in their protective roles, and the contribution of each process under certain stress condition differs among plant species (Heber 2002; Makino
et al. 2002; Rumeau et al. 2007).
7.3.3.2 Photosynthesis, Respiration, and Nitrogen Metabolisms
Photosynthesis and respiration are primary pathways of carbon and energy metabolism in plants. The balance between photosynthetic production and respiratory
breakdown of carbohydrates determines plant carbon gain and potentially growth.
These two processes are interrelated via an exchange of metabolites such as ATP,
reducing equivalents and other carbon-containing intermediates. Photosynthesis
and respiration respond to changes in environmental factors in a different manner
and thus result in an alteration of photosynthesis to cellular respiration ratio. The
effects of increased temperature and salinity on photosynthesis and respiration have
been investigated in seagrasses, and a clear shift in plant carbon metabolisms has
been observed (as discussed in the previous section). Cellular respiration in the
seagrass Z. marina is inhibited in the light, whereas the respiratory rates, as well as
expressions of respiratory genes, show diel variations (Rasmusson and Björk 2014;
Rasmusson 2015). Although it has been proposed that such variations could be a
result of an interplay between photosynthesis, photorespiration, and cellular respiration, the mechanisms involved are not completely understood. In terrestrial plants,
high CO 2 increases the respiratory breakdown of carbohydrates (Ainsworth et al.
2006; Li et al. 2013). Such an increase in respiratory activity was found in conjunction with an accumulation of carbohydrates as well as an increase in transcripts
associated with glycolysis, tricarboxylic acid cycle, and mitochondrial electron
transport (Rogers et al. 2004; Gillespie et al. 2012). The opposing utilization and
release of O 2 and CO 2 between photosynthesis, respiration, and photorespiration
make it challenging to assess the rates of these processes in the light using classical
gas exchange method. Additionally, lacunae present in all seagrasses and the potential internal recycling of both O 2 and CO 2 interfere with gas exchange measurement
and manipulations of available O 2 and CO 2 .
The interaction between carbon and nitrogen metabolisms in the context of
increasing CO 2 has been widely investigated in the terrestrial model plants (Yong
et al. 2000; Bloom et al. 2002; Cousins and Blooms 2004; Takatani et al. 2014).
Suppression of nitrate assimilation by a downregulation of nitrate and nitrite reductase activities was demonstrated in wheat exposed to elevated CO 2 (Bloom et al.
2002), whereas Arabidopsis mutant with low nitrate reductase activity exhibited
P. Buapet