142
more abundant under hypersaline stress. This work also proposed a role in repair
processes of the photosynthetic machinery for cytochrome b559 alpha subunit of
the PSII initial complex (Piro et al. 2015a).
7.2.3 Heat Stress and Its Impact on Photosynthesis
Shallow water seagrasses encounter daily and seasonal fluctuations in temperature.
The ongoing increase in mean global ocean temperatures, as well as more frequent
extreme heat events, brought about by global warming, can further affect seagrass
metabolisms. It is well established that high temperature increases respiration/photosynthesis ratios, thus negatively affecting the plant carbon balance (Marsh et al.
1986; Greve et al. 2003; Lee et al. 2007; Olsen et al. 2012; Rasmusson 2015; MarínGuirao et al. 2016) leading to reduced growth rates and biomass (Massa et al. 2009;
Olsen et al. 2012). In general, heat-tolerant plants can effectively maintain their
balance in carbon metabolisms between respiratory rates and photosynthetic rates
under high temperature (Marín-Guirao et al. 2016).
Exposure to heat shock in the seagrass Z. noltii has led to a downregulation of
certain CABs, indicating a control of energy balance or apoptosis (Massa et al.
2011). A large volume of recent works has focused on the effects of increasing temperature on the photosynthetic function of seagrasses from different temperature
regimes. Transcriptomic profiling of the seagrass Zostera marina populations from
northern and southern Europe (Franssen et al. 2011) has shown that heat stress
induced an upregulation of genes associated with heat shock proteins in both populations. However, the seagrass from the southern population (adapted to higher temperature) recovered their transcriptomic profiles after heat stress, while the seagrass
from the northern population did not recover and exhibited an upregulation of genes
associated with protein degradation. Similarly, Winters et al. (2011) compare the
effects of a simulated heat wave on the photophysiology and gene expressions of Z.
marina from the Adriatic Sea and North and Baltic Seas. All the populations showed
a similar response to an increase in temperature, e.g., F v /F m , and electron transport
rates declined except the southern population. A similar concept was investigated in
the two populations of P. oceanica from different depths (Marín-Guirao et al. 2016).
The photosynthetic function of the plants from the deep population was more sensitive to heat as shown by a larger decrease in ɸPSII, an increase in basal chlorophyll
a fluorescence, and a downregulation of the genes associated with electron transport
chain and carbon fixation. Additionally, the genes encoding for the PSII core proteins D1 and D2 were downregulated under heat stress, resulting in a halt of PSII
repair, whereas the expressions of these genes remained unchanged in shallow population. The ability to activate photoprotective mechanisms (observed as an increase
in NPQ) and enhance electron flow and carbon assimilation under heat stress was
suggested to contribute to higher heat tolerance in the shallow population.
P. Buapet
more abundant under hypersaline stress. This work also proposed a role in repair
processes of the photosynthetic machinery for cytochrome b559 alpha subunit of
the PSII initial complex (Piro et al. 2015a).
7.2.3 Heat Stress and Its Impact on Photosynthesis
Shallow water seagrasses encounter daily and seasonal fluctuations in temperature.
The ongoing increase in mean global ocean temperatures, as well as more frequent
extreme heat events, brought about by global warming, can further affect seagrass
metabolisms. It is well established that high temperature increases respiration/photosynthesis ratios, thus negatively affecting the plant carbon balance (Marsh et al.
1986; Greve et al. 2003; Lee et al. 2007; Olsen et al. 2012; Rasmusson 2015; MarínGuirao et al. 2016) leading to reduced growth rates and biomass (Massa et al. 2009;
Olsen et al. 2012). In general, heat-tolerant plants can effectively maintain their
balance in carbon metabolisms between respiratory rates and photosynthetic rates
under high temperature (Marín-Guirao et al. 2016).
Exposure to heat shock in the seagrass Z. noltii has led to a downregulation of
certain CABs, indicating a control of energy balance or apoptosis (Massa et al.
2011). A large volume of recent works has focused on the effects of increasing temperature on the photosynthetic function of seagrasses from different temperature
regimes. Transcriptomic profiling of the seagrass Zostera marina populations from
northern and southern Europe (Franssen et al. 2011) has shown that heat stress
induced an upregulation of genes associated with heat shock proteins in both populations. However, the seagrass from the southern population (adapted to higher temperature) recovered their transcriptomic profiles after heat stress, while the seagrass
from the northern population did not recover and exhibited an upregulation of genes
associated with protein degradation. Similarly, Winters et al. (2011) compare the
effects of a simulated heat wave on the photophysiology and gene expressions of Z.
marina from the Adriatic Sea and North and Baltic Seas. All the populations showed
a similar response to an increase in temperature, e.g., F v /F m , and electron transport
rates declined except the southern population. A similar concept was investigated in
the two populations of P. oceanica from different depths (Marín-Guirao et al. 2016).
The photosynthetic function of the plants from the deep population was more sensitive to heat as shown by a larger decrease in ɸPSII, an increase in basal chlorophyll
a fluorescence, and a downregulation of the genes associated with electron transport
chain and carbon fixation. Additionally, the genes encoding for the PSII core proteins D1 and D2 were downregulated under heat stress, resulting in a halt of PSII
repair, whereas the expressions of these genes remained unchanged in shallow population. The ability to activate photoprotective mechanisms (observed as an increase
in NPQ) and enhance electron flow and carbon assimilation under heat stress was
suggested to contribute to higher heat tolerance in the shallow population.
P. Buapet