23
(3) further desiccation leads to a loss of water splitting activity and, eventually, the
complete loss of fluorescence photosystem II reaction centers; and (4) intersystem
electron transport begins almost immediately after rehydration while the recovery
of water splitting requires several minutes. This final point was confirmed in a
detailed study performed by Contreras-Porcia et al. (2011) on the desiccation-tolerant red algae Py. orbicularis. Specifically, the photosynthetic efficiency and electron transport flux per cross of Py. orbicularis returned to the basal levels only
5 min after rehydration.
An extensive study on various algal species sampled from numerous locations
within the Chilean rocky intertidal zone (Flores-Molina et al. 2014) demonstrated that
the mid-intertidal algae species Mazzaella laminarioides and Scytosiphon lomentaria
(Ectocarpales) recover basal photosynthetic activity after rehydration. However, algae
from the lower intertidal zone, including Ulva compressa, L. spicata, and Gelidium
rex, do not fully recover from desiccation stress. This would partly explain the positions of these algal species within the rocky intertidal zone of the Chilean coast.
Furthermore, researchers have posited that the poorer photosynthetic performance of
sensitive species during desiccation/rehydration cycles is generated by disarrayed
photosynthetic machinery and not by a photoinhibition mechanism.
Transcriptomic and proteomic studies performed on Py. orbicularis indicate a
downregulation of photosynthesis-related RNAs and proteins such as RubisCO,
photosystem I and II proteins, and ferredoxin-NADP
+
during stressful periods
(Contreras-Porcia et al. 2013; López-Cristoffanini et al. 2015). These downregulated expressions during desiccation, together with rapid expression recoveries during rehydration, suggest homoiochlorophyllous-like behavior, which is the storing
of proteins by dismantling under stressful conditions.
2.2.2 Morphological Changes and the Accumulation
of Compatible Solutes
Resurrection plants are known for leaf curling when subjected to desiccation stress,
a mechanism also observed in algal species suffering a cellular water deficit. Like
resurrection plants, desiccated algal tissue contains a low cellular water content and,
as observed through optical microscopy, a reduced cellular volume (~30–60% of the
non-stressed volume). Sensitive species from the Chilean coast show slightly
reduced cellular volumes (25–43%), as well as ultrastructural damage, under air
exposure. Specifically, L. spicata does not recover the fine structure of organelles
and cellular components after rehydration (Flores-Molina et al. 2014). In Py. orbicularis, the normal greenish-red color of cells is replaced by dark purple, and cells
become tightly folded, stiff, and brittle (Contreras-Porcia et al. 2011). This reduction and folding of cells may occur due to reduced contents of microtubule and
microfilament proteins, as previously observed in resurrection plants (Pressel et al.
2006; Oliver et al. 2011; Cruz de Carvalho et al. 2014).
As in Py. orbicularis, desiccation stress drastically alters the actin cytoskeleton of
Klebsormidium crenulatum (Charophyta) (Holzinger et al. 2011). Proteomic and
2 Tolerance Pathways to Desiccation Stress in Seaweeds
(3) further desiccation leads to a loss of water splitting activity and, eventually, the
complete loss of fluorescence photosystem II reaction centers; and (4) intersystem
electron transport begins almost immediately after rehydration while the recovery
of water splitting requires several minutes. This final point was confirmed in a
detailed study performed by Contreras-Porcia et al. (2011) on the desiccation-tolerant red algae Py. orbicularis. Specifically, the photosynthetic efficiency and electron transport flux per cross of Py. orbicularis returned to the basal levels only
5 min after rehydration.
An extensive study on various algal species sampled from numerous locations
within the Chilean rocky intertidal zone (Flores-Molina et al. 2014) demonstrated that
the mid-intertidal algae species Mazzaella laminarioides and Scytosiphon lomentaria
(Ectocarpales) recover basal photosynthetic activity after rehydration. However, algae
from the lower intertidal zone, including Ulva compressa, L. spicata, and Gelidium
rex, do not fully recover from desiccation stress. This would partly explain the positions of these algal species within the rocky intertidal zone of the Chilean coast.
Furthermore, researchers have posited that the poorer photosynthetic performance of
sensitive species during desiccation/rehydration cycles is generated by disarrayed
photosynthetic machinery and not by a photoinhibition mechanism.
Transcriptomic and proteomic studies performed on Py. orbicularis indicate a
downregulation of photosynthesis-related RNAs and proteins such as RubisCO,
photosystem I and II proteins, and ferredoxin-NADP
+
during stressful periods
(Contreras-Porcia et al. 2013; López-Cristoffanini et al. 2015). These downregulated expressions during desiccation, together with rapid expression recoveries during rehydration, suggest homoiochlorophyllous-like behavior, which is the storing
of proteins by dismantling under stressful conditions.
2.2.2 Morphological Changes and the Accumulation
of Compatible Solutes
Resurrection plants are known for leaf curling when subjected to desiccation stress,
a mechanism also observed in algal species suffering a cellular water deficit. Like
resurrection plants, desiccated algal tissue contains a low cellular water content and,
as observed through optical microscopy, a reduced cellular volume (~30–60% of the
non-stressed volume). Sensitive species from the Chilean coast show slightly
reduced cellular volumes (25–43%), as well as ultrastructural damage, under air
exposure. Specifically, L. spicata does not recover the fine structure of organelles
and cellular components after rehydration (Flores-Molina et al. 2014). In Py. orbicularis, the normal greenish-red color of cells is replaced by dark purple, and cells
become tightly folded, stiff, and brittle (Contreras-Porcia et al. 2011). This reduction and folding of cells may occur due to reduced contents of microtubule and
microfilament proteins, as previously observed in resurrection plants (Pressel et al.
2006; Oliver et al. 2011; Cruz de Carvalho et al. 2014).
As in Py. orbicularis, desiccation stress drastically alters the actin cytoskeleton of
Klebsormidium crenulatum (Charophyta) (Holzinger et al. 2011). Proteomic and
2 Tolerance Pathways to Desiccation Stress in Seaweeds