17
2.1.2 Differential Buffering Capacities of Seaweeds
Against the Overproduction of ROS and Cellular
Damage During Desiccation Stress
The main source of injury during emersion (low tide) for sessile marine organisms
such as seaweeds is osmotic imbalance with the subsequent loss of cellular water
content. Moreover, depending on climatic and oceanographic conditions, other
types of stressors could also play important roles in algal injury. During air exposure
and water depletion, ROS are produced in excess, surpassing the buffering capacities of cells and resulting in the oxidation of macromolecules such as lipids and
proteins (Foyer and Noctor 2009). ROS are directly produced by O 2 excitation and
the subsequent formation of singlet oxygen, or by the transfer of one, two, or three
electrons to O 2 , which results in the formation of superoxide radicals, hydrogen
peroxide, or hydroxyl radicals, respectively. It is worth mentioning that ROS are a
normal by-product of the metabolism and function, for example, as signaling molecules, in addition to participating in local immune responses to parasitic and herbivorous attacks (Baker and Orlandi 1995). In non-tolerant algae species, water loss
through an osmotic imbalance can also cause tearing of the plasmalemma from the
cell wall, thus threatening cell integrity (Flores-Molina et al. 2014). In fact, cellular
dehydration resulting from desiccation or emersion stress in general increases electrolyte concentrations in the cell, altering membrane structures such as thylakoids
(Kim and Garbary 2007).
Desiccation stress-tolerant species, such as Pyropia orbicularis [formerly Pyropia
columbina (Bangiales, Rhodophyta)] (Ramírez et al. 2014) collected from the upper
intertidal zone of a southeast Pacific shoreline of Central Chile (18°–53°S), can tolerate water loss near 96% (Contreras-Porcia et al. 2011). Despite an overproduction
of ROS such as hydrogen peroxide (H 2 O 2 ), this species is able to increase the activity
of diverse antioxidant enzymes and lower the production of oxidized proteins during
desiccation. Contreras-Porcia et al. (2011) also demonstrated that Py. orbicularis
decreases photosynthetic activity and chlorophyll content, but maintains high levels
of phycocyanin and phycoerythrin, during rehydration, as well as evidencing rapid
photosynthetic apparatus activity recovery during rehydration.
In addition to the activation of antioxidant enzymes, a low production of oxidized macromolecules can result from the production of lipid- and water-soluble
compounds, which also regulate ROS levels during dehydration (Noctor and Foyer
1998; Asada 1999; Wang et al. 2009). In fact, macroalgae collected from lower
intertidal zones of Central Chile and treated with algal extracts from desiccated Py.
orbicularis can complete post-germination development under desiccation stress
treatments (Contreras-Porcia et al. 2012). This extract-mediated adaptation contrasts with the normal response of Lessonia spicata (Laminariales), the least tolerant algal species studied. Specifically, without the extract treatment, when L. spicata
is exposed to desiccation stress (2 h/day), it is able to germinate but cannot complete
post-germination development.
A number of comparisons have been conducted between dehydrated and hydrated
states in the most desiccation-tolerant seaweed Py. orbicularis (Contreras-Porcia
2 Tolerance Pathways to Desiccation Stress in Seaweeds
2.1.2 Differential Buffering Capacities of Seaweeds
Against the Overproduction of ROS and Cellular
Damage During Desiccation Stress
The main source of injury during emersion (low tide) for sessile marine organisms
such as seaweeds is osmotic imbalance with the subsequent loss of cellular water
content. Moreover, depending on climatic and oceanographic conditions, other
types of stressors could also play important roles in algal injury. During air exposure
and water depletion, ROS are produced in excess, surpassing the buffering capacities of cells and resulting in the oxidation of macromolecules such as lipids and
proteins (Foyer and Noctor 2009). ROS are directly produced by O 2 excitation and
the subsequent formation of singlet oxygen, or by the transfer of one, two, or three
electrons to O 2 , which results in the formation of superoxide radicals, hydrogen
peroxide, or hydroxyl radicals, respectively. It is worth mentioning that ROS are a
normal by-product of the metabolism and function, for example, as signaling molecules, in addition to participating in local immune responses to parasitic and herbivorous attacks (Baker and Orlandi 1995). In non-tolerant algae species, water loss
through an osmotic imbalance can also cause tearing of the plasmalemma from the
cell wall, thus threatening cell integrity (Flores-Molina et al. 2014). In fact, cellular
dehydration resulting from desiccation or emersion stress in general increases electrolyte concentrations in the cell, altering membrane structures such as thylakoids
(Kim and Garbary 2007).
Desiccation stress-tolerant species, such as Pyropia orbicularis [formerly Pyropia
columbina (Bangiales, Rhodophyta)] (Ramírez et al. 2014) collected from the upper
intertidal zone of a southeast Pacific shoreline of Central Chile (18°–53°S), can tolerate water loss near 96% (Contreras-Porcia et al. 2011). Despite an overproduction
of ROS such as hydrogen peroxide (H 2 O 2 ), this species is able to increase the activity
of diverse antioxidant enzymes and lower the production of oxidized proteins during
desiccation. Contreras-Porcia et al. (2011) also demonstrated that Py. orbicularis
decreases photosynthetic activity and chlorophyll content, but maintains high levels
of phycocyanin and phycoerythrin, during rehydration, as well as evidencing rapid
photosynthetic apparatus activity recovery during rehydration.
In addition to the activation of antioxidant enzymes, a low production of oxidized macromolecules can result from the production of lipid- and water-soluble
compounds, which also regulate ROS levels during dehydration (Noctor and Foyer
1998; Asada 1999; Wang et al. 2009). In fact, macroalgae collected from lower
intertidal zones of Central Chile and treated with algal extracts from desiccated Py.
orbicularis can complete post-germination development under desiccation stress
treatments (Contreras-Porcia et al. 2012). This extract-mediated adaptation contrasts with the normal response of Lessonia spicata (Laminariales), the least tolerant algal species studied. Specifically, without the extract treatment, when L. spicata
is exposed to desiccation stress (2 h/day), it is able to germinate but cannot complete
post-germination development.
A number of comparisons have been conducted between dehydrated and hydrated
states in the most desiccation-tolerant seaweed Py. orbicularis (Contreras-Porcia
2 Tolerance Pathways to Desiccation Stress in Seaweeds