25
existing research indicates that similar mechanisms occur in algae subjected to desiccation stress, information that contributes toward explaining the vertical distribution of intertidal seaweed species.
2.2.4 Increased Antioxidant Activity
Along with the modifications and effects mentioned in the previous subsections,
desiccation can also cause oxidative stress . This condition occurs when there is an
uncontrolled production of free oxygen radicals that consequently increase the levels of ROS. Algae have successfully developed scavenging mechanisms to prevent
harmful ROS overproduction, and the first study on antioxidant responses to desiccation stress in algae analyzed Stictosiphonia arbuscula (Ceramiales) individuals
collected from the upper and lower rocky intertidal zones of a New Zealand beach
(Burritt et al. 2002). The authors showed that desiccation stress triggered an
organism- wide antioxidant response, although glutathione reductase and AP
enzyme activities were greater in individuals sampled from the upper rocky intertidal zones. This also correlates with the finding that low-band specimens produce
more hydrogen peroxide than high-band ones.
An in-depth analysis of antioxidant responses in Py. orbicularis established that
this alga increases the production of glutathione reductase, AP, catalase (CAT), thioredoxin (TRX), dehydroascorbate reductase, peroxiredoxin (PRX), and CAT, PRX,
and TRX transcripts, among other factors, under desiccation (Contreras-Porcia et al.
2011; Fierro et al. 2017). Interestingly, Western-blot analyses of desiccated Py.
orbicularis fronds display low PRX protein levels, and in rehydrated specimens,
PRX activity drops to undetectable levels. PRXs belong to the thiol-dependent peroxidase family and are known to attenuate oxidative stress and modulate redoxdependent signaling cascades (Rouhier and Jacquot 2002; Tripathi et al. 2009; Dietz
2011). Therefore, the observed differential inductions of PRX could be involved in
the transduction of signals by means of ROS, which are needed for the genetic activation of tolerance factors during air exposure.
Recently, Guajardo et al. (2016) showed that under desiccation stress, free
abscisic acid (ABA) levels in Py. orbicularis were four- to sevenfold higher than
sensitive species. Using the ABA inhibitors sodium tungstate and ancymidol, ABA
was found to regulate the activation of antioxidant enzyme activities during desiccation (AP, CAT, and PRX), concomitant with low lipid peroxidation and high cell
viability. These results demonstrate the participation of ABA in the regulation of
desiccation tolerance in seaweeds and suggest that regulatory mechanisms with
ABA signaling could be of great importance for the adaptation of these organisms
to environmental stress.
López-Cristoffanini et al. (2015) detected the proteins SOD and lactoylglutathione lyase, also known as glyoxalase I (GlyI), in Py. orbicularis. GlyI is key to
detoxifying the methylglyoxal that may be overproduced during stressful conditions, including desiccation (Blomstedt et al. 1998; Hossain et al. 2009). A recent
study by Fierro et al. (2016) assessed methylglyoxal production and GlyI activity in
2 Tolerance Pathways to Desiccation Stress in Seaweeds
existing research indicates that similar mechanisms occur in algae subjected to desiccation stress, information that contributes toward explaining the vertical distribution of intertidal seaweed species.
2.2.4 Increased Antioxidant Activity
Along with the modifications and effects mentioned in the previous subsections,
desiccation can also cause oxidative stress . This condition occurs when there is an
uncontrolled production of free oxygen radicals that consequently increase the levels of ROS. Algae have successfully developed scavenging mechanisms to prevent
harmful ROS overproduction, and the first study on antioxidant responses to desiccation stress in algae analyzed Stictosiphonia arbuscula (Ceramiales) individuals
collected from the upper and lower rocky intertidal zones of a New Zealand beach
(Burritt et al. 2002). The authors showed that desiccation stress triggered an
organism- wide antioxidant response, although glutathione reductase and AP
enzyme activities were greater in individuals sampled from the upper rocky intertidal zones. This also correlates with the finding that low-band specimens produce
more hydrogen peroxide than high-band ones.
An in-depth analysis of antioxidant responses in Py. orbicularis established that
this alga increases the production of glutathione reductase, AP, catalase (CAT), thioredoxin (TRX), dehydroascorbate reductase, peroxiredoxin (PRX), and CAT, PRX,
and TRX transcripts, among other factors, under desiccation (Contreras-Porcia et al.
2011; Fierro et al. 2017). Interestingly, Western-blot analyses of desiccated Py.
orbicularis fronds display low PRX protein levels, and in rehydrated specimens,
PRX activity drops to undetectable levels. PRXs belong to the thiol-dependent peroxidase family and are known to attenuate oxidative stress and modulate redoxdependent signaling cascades (Rouhier and Jacquot 2002; Tripathi et al. 2009; Dietz
2011). Therefore, the observed differential inductions of PRX could be involved in
the transduction of signals by means of ROS, which are needed for the genetic activation of tolerance factors during air exposure.
Recently, Guajardo et al. (2016) showed that under desiccation stress, free
abscisic acid (ABA) levels in Py. orbicularis were four- to sevenfold higher than
sensitive species. Using the ABA inhibitors sodium tungstate and ancymidol, ABA
was found to regulate the activation of antioxidant enzyme activities during desiccation (AP, CAT, and PRX), concomitant with low lipid peroxidation and high cell
viability. These results demonstrate the participation of ABA in the regulation of
desiccation tolerance in seaweeds and suggest that regulatory mechanisms with
ABA signaling could be of great importance for the adaptation of these organisms
to environmental stress.
López-Cristoffanini et al. (2015) detected the proteins SOD and lactoylglutathione lyase, also known as glyoxalase I (GlyI), in Py. orbicularis. GlyI is key to
detoxifying the methylglyoxal that may be overproduced during stressful conditions, including desiccation (Blomstedt et al. 1998; Hossain et al. 2009). A recent
study by Fierro et al. (2016) assessed methylglyoxal production and GlyI activity in
2 Tolerance Pathways to Desiccation Stress in Seaweeds